urutau

Research & design by Joseph the parrot

Documentation by RSmith28
Published by:
The Gatalog
August 20th, 2024
Document version: 1.0.0

Author of this document:

RSmith28
Designer of the Urutau:
Joseph The Parrot
Emails: JosephTheParrot@protonmail.com and riflesmith28@protonmail.com
Please use our PGP keys when emailing us. All unencrypted emails will be ignored.

https://cariocaworks.com
https://thegatalog.com

This work is marked with CC0 1.0. No copyright is reserved on the Urutau or any of its
associated documents.

Per our interpretation of FOSS standards, we did not

put any noncommercial stipulations on the Urutau.
However, if you paid any person or website to access
this digital work, you got ripped off. Please seek out
a refund by any means available.
Special Thanks To:
All the beta testers from AWCY? and The Gatalog. Without their help, the Urutau
would never have existed.
The following donors:
Maple
Austin Thomas Jones
Nestor Vargas
lvlggo
Zenitheus
Rynax
Sandmann
Tony Hurricane
And 39 Anonymous Individuals

ImmortalRevolt, AdvancedPayment, Derwoodvw and many other designers whose

creations inspired and influenced the Urutau design.
The schoolteachers who told us we could be anything we wanted when we grew up.
The People who didn’t believe us.
And, most importantly, JStark1809, a man who lived free.
Urutau
Designer: Joseph The Parrot
Designed: 2021-2024
Type: Bullpup Pistol Caliber Carbine
Mass (Empty Magazine Included): about 2830g
Default Overall Length: 475mm
Default Barrel Length: 250mm
Cartridge: 9x19mm Luger/Parabellum
Action: Closed-Bolt Straight-Blowback
Feed system: 3D Printed 30 Round Magazine or any Scorpion Evo 3 Magazine
 Scientia Potentia Est!
Knowledge is Power!
We hope you appreciate all the time, resources, and effort that we put into the Urutau
as well as the risks we assumed in its testing and publication.

To sustain our efforts in undermining global firearm prohibition, please propagate the
Urutau file package as much as possible unless/until it is superseded by something
better. To avoid implicating yourself, please do so anonymously or in a way that
makes it difficult to track you down. It is our collective duty to ensure these files
are always freely available to everyone.

If you had success in producing your Urutau and/or want to perpetuate our cause,
please consider donating to Zé Carioca. All donated funds will help with development
and improvements to the Urutau and future designs. You can find his Monero (XMR)
address below.

XMR
 Table of Contents
Safety Advisory........................................................................................................... 7
American Legal Warning............................................................................................9
OpSec & Obfuscation............................................................................................... 12
Machines & Tools......................................................................................................20
Ammunition............................................................................................................... 24
Barrel..........................................................................................................................26
Materials.....................................................................................................................28
3D Printed Parts........................................................................................................ 36
Bolt Carrier Assembly...............................................................................................52
Hammer Spring Winding..........................................................................................61
Lower Assembly........................................................................................................64
Rear Cap Assembly...................................................................................................75
Upper Assembly........................................................................................................79
Iron Sights..................................................................................................................85
Magazine Assembly.................................................................................................. 88
Final Assembly..........................................................................................................90
Function Testing........................................................................................................95
Maintenance...............................................................................................................97
Troubleshooting........................................................................................................98
Technical Aspects and Design Choices................................................................100
 Safety Advisory
You are about to manufacture a firearm that was designed, tested, and published by
strangers on the internet. While we hope you find the Urutau useful and the contents
of this document informative, please understand that this file package makes
absolutely no promises of success or safety in any of your undertakings.

The four basic rules of firearm safety are as follows:

1. Treat every firearm as if it is loaded until you have personally verified
otherwise.
2. Always keep firearms pointed in a safe direction.
3. Keep your finger off the trigger until you are ready to fire.
4. Always be aware of what is ahead of and beyond your target.

On top of those safety rules, please adhere to the following guidelines.

• Wear hearing and eye protection when firing the Urutau. Shooting without eye
protection is risky, like driving without a seatbelt, but shooting without hearing
protection is painful and will damage your sense of hearing.
• Do not cock the Urutau’s hammer with the safety switch on, in the rear position.
Doing so may damage your fire control group components.
• Replace parts and components as they become significantly worn.
• While we never experienced any issues with the hammer spontaneously breaking
loose, storing the Urutau loaded with a round in the chamber is not recommended.
• Keep your hands clear of the ejection port when charging or firing the Urutau.
• Inspect your ammunition before using it.
• Do not blindly use components and materials in your Urutau without first making sure
their dimensions and properties fulfill the design specifications in this document.
• If you make experimental changes to the design, wear other protective equipment in
case of unforeseeable malfunctions. Consider firing the weapon remotely by securely
mounting it to a vise and pulling the trigger with a string.
• Check your barrel for obstructions before firing. To check safely, remove the rear cap
and bolt carrier assembly, and then look down the barrel from the breech-end. If there
is an obstruction, do not try to "shoot it out." Use a rod and hammer to tap it out of the
barrel.
• If you notice a significant difference in sound or recoil after firing, stop. This may be a
sign of a squib load, a primed cartridge without powder. If this happens, check your
barrel for obstructions.
• To minimize lead exposure, only shoot your Urutau in well-ventilated areas if possible.
• Keep your Urutau inaccessible to those too incompetent to handle it.
• While the safety switch should be utilized when possible, it should not be used as a
replacement for any of these rules or guidelines.
• Do not shoot firearms into the air. The Urutau is not a noisemaker. The bullets have to
go somewhere.
• If you are intoxicated, significantly tired, sick, or under emotional distress, do not
handle a weapon.

FOLLOW ALL THE INSTRUCTIONS IN THIS DOCUMENT CAREFULLY.

DO NOT ASSUME ANYTHING IS OPTIONAL UNLESS WE EXPLICITLY STATE

SO.

EVERYTHING WE WROTE IS HERE FOR A REASON.

PLEASE DON'T BE AN IDIOT.

Got all of that? Good.

American Legal Warning
We are not lawyers, and no part of this document is to be construed as legal advice.
Generally, the American federal government does not prohibit the private manufacture
of firearms, but depending on the characteristics of a firearm, it may or may not
require registration to make and own legally. The purpose of this section is to manage
the risk of American Urutau builders inadvertently breaking the law.

Short-Barreled Rifle (SBR)

Depending on the configuration you choose for your Urutau, you may create a firearm
that meets the definition of a short-barreled rifle (SBR). An SBR is defined as a
firearm that is fired from the shoulder with a barrel length less than 16 inches and/or
and overall length less than 26 inches. (18 USC § 921(a)(8))
Without considering state and local restrictions, SBRs are legal to own provided that
they are compliant with federal law. Compliance requires submitting and receiving
approval on an ATF Form 1 and serializing your lower receiver in accordance with the
National Firearms Act Handbook chapter 7. Please see the NFA/GCA section for
more details.
To avoid manufacturing an SBR, assemble your Urutau with the extended rear cap to
keep its overall length over 26 inches, and ensure that your barrel is greater than or
equal to 16 inches. It is possible to use a shorter rear cap in tandem with a longer
barrel to keep the overall length over 26 inches, but the shorter length of pull may feel
uncomfortable with a longer barrel.
National Firearms Act (NFA) / Gun Control Act (GCA)
If you want to make an SBR, you are legally required to register your Urutau with the
ATF. If you decide to do so, you will need to submit fingerprints, take a portrait of
yourself, fill out an application, pay $200, and wait a period of time for your application
to receive approval. Only once your application is approved, you can make your
Urutau into an SBR.
To register your Urutau, fill out ATF Form 5320.1, also referred to as “Form 1.” The
easiest and fastest way to do this is on the ATF eForms website. Electronic
fingerprints, while not a requirement, have an extra upfront cost, but they are
significantly more convenient and speed up approval times. You will also be required
to serialize your lower receiver. Please review the National Firearms Act Handbook
chapter 7 for specific requirements.
For more information about the process, please do your own research. ATF
requirements for your application can change with little to no notice at any time. With
further questions, please consult with an attorney.
If this sounds like too much to handle, do not worry. As stated, it is possible to make
your Urutau in such a way that it does not require registration.

State and Local Restrictions / Prohibitions

Different state and local jurisdictions may restrict or prohibit the weapons you can
legally own and/or manufacture. Please familiarize yourself with your state and local
laws before attempting to manufacture the Urutau.

Other Laws
The risks of Americans ignorantly manufacturing SBRs and firearms prohibited by
state and local laws are one of our biggest concerns in publishing the Urutau.
However, those are far from the only laws to consider. Please become familiar with all
applicable federal, state, and local weapon laws before manufacturing the Urutau or
coming into possession of any firearm.

What if my SBR wears out or breaks?

You are required to completely destroy the serialized lower receiver and send a notice
to the ATF that it is completely destroyed. To legally make a new one, you are
required to file a new Form 1. Destroying your serialized part and then making a new
one with the same serial number and tax stamp is illegal. Of course, you can probably
infer that the efficacy of this law is questionable, but take that for what you will.

What if I don’t care about all this legal stuff?

Please reconsider. Do not underestimate what a felony on your record will do to you.
A felony conviction will keep you from voting, keep you from serving in the military,
keep you from attaining or force you to forfeit professional licenses, complicate finding
a job, cost you in fines and legal fees, send you to prison, and worst of all, keep you
from legally owning a firearm.

What if I still don’t care?

Well, shoot. I guess you don’t. In that case, please avoid getting caught.
At the very least, watch "Don't Talk to the Police", a law lecture by Regent University
Law Professor James Duane and "10 Rules for Dealing with Police", a video by Flex
Your Rights, an American nonprofit organization. Also, please read OpSec &
Obfuscation, the next section.
 OpSec & Obfuscation
The Urutau is designed for a global audience, and some of its builders will actively
defy the laws in their jurisdictions. Manufacturing a firearm illegally is an inherently
risky activity, and the purpose of this section is twofold. It intends to help you minimize
the risk of coming under scrutiny and to help you control damage if an investigation
against you occurs. The contents of this section consider both inward-facing and
outward-facing evidence as well as managing interpersonal relationships and
communication, or lack thereof, with authorities of the state.
Some of the information in this section may seem onerous to comply with. Whether or
not you do depends on the potential penalties and your risk tolerance. The
applicability of this information depends upon your jurisdiction’s rules of evidence,
right to remain silent, right to protection from unwarranted searches, and right to legal
representation, which vary around the world.
No matter the difficulty or applicability, the purpose of this section is to help you avoid
death before you have the chance to live free.

Special thanks to the West Midlands Police and the BBC’s show “Forensics: The Real
CSI” for inspiring or confirming the contents of this document! Watch Season 4,
Episode 3 if you are curious.
This section is written to honor David Biddell-Portman, an English man who did
absolutely nothing wrong!
 Rule #1:
Keep Quiet
"People can tame all kinds of animals, birds, reptiles, and fish, but no one can tame
the tongue. It is restless and evil, full of deadly poison." (James 3:7-8)
The easiest way for the authorities to catch you manufacturing and/or possessing an
illegal firearm is to tell other people about it. Even if you are talking with your best
friend, let us caution you that the momentary dopamine rush you feel from telling
them your secret is not worth the endless anxiety you will feel knowing that they are
now a liability.
In case that is not clear, do not communicate your plan to manufacture or that you
possess a firearm with anyone. Do not hint at it. Do not joke about it. Do not show it
off. Do not brag about it on social media. Do not attempt to sell it. Absolutely do not do
an interview with a journalist.
Do not commit more than one crime at a time. As silly as this may sound, the point is
that manufacturing and/or possessing a clandestine, illegal firearm is a lot less likely
to draw unwanted attention if you are not simultaneously engaging in organized
crime, drug crime, violent crime, or other illegal shenanigans.
Most importantly, if you are ever accosted or arrested by the authorities for any
reason, whether you know you are guilty or not, most developed countries afford you
the right to protection from unwarranted searches, the right to remain silent, and the
right to legal counsel. Please research your country’s laws to determine if and how
these rights apply to you, at your home, in public, or in the courtroom. Flexing your
rights may make you “look guilty,” but in many countries that afford people these
rights, you invoking them cannot be used as evidence against you.
 Rule #2:
Minimize Evidence
For the purposes of this section, we will designate evidence as physical, inward-
facing computer systems, and outward-facing computer systems. Physical evidence
is any tangible material which would directly or indirectly incriminate you. Inward-
facing computer systems include the contents of your desktop computer, laptop
computer, mobile phone, or any personal digital device of capable of retaining
information. Outward-facing computer systems include the various websites and
online services you interact with. Computer systems and physical evidence are
serious liabilities to you. If not properly managed, they can provide evidence that is
highly telling of your behavior, both before and after an investigation begins.

Physical Evidence
If you are caught red-handed, you are more than likely going to find yourself in legal
trouble. However, if a firearm and ammunition is not in your immediate possession,
the laws in your jurisdiction may afford you protection if you have plausible deniability
that a firearm is yours. Please investigate options to cache your weapon in as remote
an area as possible. Beware that canines can be trained to sniff out firearms and
ammunition, so keeping it stored in your home may be unwise.
Think carefully before throwing away gun parts or any 3D printer waste in the
garbage. If a part you are throwing away is recognizable, or worse, functional, you
may come under serious scrutiny. However, in some jurisdictions, something as
simple as discarded support structures could become part of an investigation.
Fortunately, with enough heat and air, PLA burns with little smoke, though it makes a
goopy mess. Still, this is the cheapest method for 3D printed part and waste disposal.
 The courtroom admissibility of fingerprint and DNA evidence varies by jurisdiction, but
it is useful to infer your possession or creation of an object. Manage fingerprints by
wearing gloves when handling firearm components, especially metal and glass ones.
DNA evidence is harder to control, but it is easier to obfuscate. Rub a cloth on a
surface contacted by the public, like a hand railing for example, and then rub the cloth
on the inside and outside of the weapon. While this is untested, it may confuse an
investigation.
In some jurisdictions, it is harder to prosecute for possession of a firearm if the
authorities cannot prove that the firearm is viable. If this is the case in your
jurisdiction, consider removing the firing pin, fire control group components, or other
parts to render the firearm useless on its own, and thoroughly hide the smaller pieces
elsewhere.
Do not print any documents or create any handwritten notes related to the firearm you
are manufacturing. If you already have, burn the documents or soak them in a
container of water and use your hands to knead them to a pulp. Most conventional
paper shredders are inadequate for destroying printed information, but these other
methods are cheap and very effective.

Inward-Facing Computer Systems

In some particularly tyrannical jurisdictions, like Canada, Australia, or the state of New
Jersey, the law may prohibit possession of firearm-related technical information
outright. Even if this is not the case, the contents of your personal devices are highly
telling of your behavior, and if you cannot legally manufacture a firearm, you should
treat firearm-related digital files with serious caution. For this reason, prioritize
securing or avoiding use of these devices when manufacturing a firearm.
Personal cybersecurity is a continually evolving issue, and this guide is not
comprehensive, nor can we guarantee that it will protect your privacy. Instead, we
intend to make some general recommendations to secure your personally owned
devices to a point where it may prevent extraction of incriminating information by a
law-enforcement agency.
1. Encrypt your computer’s hard drive with a free tool like Veracrypt. Features of
Veracrypt include full disk encryption with pre-boot authentication and the option of a
 decoy OS in case you are forced to give up the password. (By “forced,” we mean that
you are in a situation where you do not have the right to remain silent.) LUKS
encryption with a system running a GNU+Linux distribution is also a viable option,
though it does not include the ability to create a decoy OS. In case the contents of this
computer become inaccessible or are destroyed, we recommend backing up
irreplaceable, innocuous personal files and/or utilizing a secondary computer.
Remember that pre-boot authentication is useless if your computer is apprehended
while it is turned on. After encrypting your computer, shut it down while it is not in use.
If you cannot encrypt your entire computer, at an absolute minimum, use a free tool
like Cryptomator to encrypt anything incriminating.
2. If you have digital files on an unencrypted computer or storage device that you need
to destroy, use a free tool like BleachBit. Features of BleachBit include secure
deletion of files and comprehensive overwriting of empty file storage space. This is
important if you already tried to delete files without BleachBit, as recoverable copies
may continue to exist on your hard drive. BleachBit is especially important to securely
remove GCODE files from the SD card you use with your 3D printer.
3. Use a distribution of the GNU+Linux operating system like Debian or Fedora, for
example. While many would argue over which distribution is “the best,” we
recommend either of these two for their general respect of user privacy, aversion to
proprietary software, and their ease of use. Use of these operating systems will
minimize the risk of intentional backdoors related to proprietary software, and the
operating system makes a less-lucrative target due to its relative obscurity. You are
welcome to use any other GNU+Linux distribution, but be aware that it may contain
undesired, proprietary software or other vulnerabilities. Most GNU+Linux distributions
are compatible with slicers like Cura, Slic3r, and Bambu Studio, but you may need to
utilize a Windows virtual machine if you want to run a proprietary CAD program.
4. Do not depend on any “cloud” file storage services, like Dropbox, Google Drive,
iCloud, or Microsoft OneDrive, for example. There is no such thing as “the cloud.” It is
only someone else’s computer. The degree to which these services will respect your
privacy in general is always in question, but these services absolutely will not protect
your privacy if they are issued a subpoena from a law-enforcement agency. If you
absolutely cannot avoid using one of these file storage services, use a tool like
Cryptomator to encrypt your files before uploading them.
5. Insulate your computer from the internet as much as possible. Do not open any
firearm-related files or programs until it is offline. Obviously, you need internet access
to download the files to make your firearm, but once you have all data and software
downloaded to your system, keep it off the internet. You never know what might be
running on your computer that could give you away, but insulating your computer from
the internet is the most effective way to keep it from leaking information.
6. Do not involve your personal mobile phone. Those proprietary pieces of junk often
have backdoors open for law enforcement use. Do not use it or take it with you in the
pursuit of any firearm-related activities. If you are making a firearm for exclusively
personal use, you should not need it anyway. If you will not follow this rule, consider
buying a phone which you can install GrapheneOS to. As of writing, there is no
evidence that up-to-date versions of GrapheneOS have been compromised by any
organization specializing in mobile device data extraction. GrapheneOS also includes
many security-oriented features. For example, in case you are under duress, you can
set a secondary PIN or password which, when entered, wipes your device clean.

Outward-Facing Computer Systems

If you are in a legally precarious situation, please avoid using any public chatroom
related to privately manufactured firearms. Considering Rule #1 implications,
everything one writes on these platforms are likely monitored and logged in many
different locations. We have no information on the backend security of these
platforms, so please treat them with serious caution. However, we understand that
this document cannot foresee every question or issue you may experience with the
Urutau. We also understand and appreciate that you may want to innovate on the
Urutau and share your creations with others.
If you have a question, issue, or innovation you would like to share with Zé Carioca
and/or RSmith28, you can email them directly with the addresses included in the
Preface section. When contacting us, please use our included PGP keys to encrypt
your message, and include your public key in the first email you send us.
Unencrypted emails will be ignored. If you are smart enough to make an Urutau,
we trust that you can figure out how to utilize PGP encryption with a program like
Kleopatra, a program for creating, managing, and utilizing PGP keys. Please read the
readme document in the PGP Keys & Contact Info directory before attempting to
contact us.
To contact us, we recommend accessing ProtonMail over Tor. Proton has given law
enforcement user IP address in the past, but accessing their service exclusively over
Tor should alleviate this concern. To access Tor, we recommend using TailsOS.
TailsOS is a GNU+Linux distribution which is designed to connect you to The Onion
Router (Tor) network with little other functionality, and it is generally the most secure
way to access Tor. It runs off a USB drive and does not require that you overwrite the
contents of your computer or configure dual-booting. TailsOS also includes a copy of
Kleopatra preinstalled. If you want to access The Gatalog chatroom, knowing the risks
involved, it is accessible over Tor & TailsOS as well. Do not share any personal details
that the authorities can use to correlate your identity, and use extreme caution to strip
metadata from any files that you share.
Articles of evidence from online actions, like online purchases for example, are
unavoidable when manufacturing a firearm. Purchases of items like filament, nuts,
and screws are unlikely to draw suspicion, but some items like ammunition
components, hydraulic pipe, specialized springs, and other accessories may warrant
caution. These are purchases that, while not necessarily illegal, deniability of illegal
use is less plausible. We call these “potentially concerning purchases.” It only
takes one potentially concerning purchase to trigger an investigation, but the more
potentially concerning purchases one makes, the easier it is to correlate their
intentions. For example, if one were to purchase thick-wall hydraulic “explosion-proof”
tubing, magazine springs, an AR15 hammer spring, bullets, casings, primers, Hilti
nailgun cartridges, a red-dot optic, a solvent trap, a sling, and a gun cleaning kit, can
you guess what they are doing?
Before making a potentially concerning purchase, take time to exhaust all your
homemade alternatives. As time goes on, what is feasible to manufacture at home will
change, hopefully for the better. In cases where you must make a potentially
concerning purchase, consider potential anonymous payment and shipping methods,
which vary depending on where you are located. Refer to the story, John Smith
Practices Good OpSec for a general example of purchasing and shipping a product
without leaving a digital paper trail.
 Rule #3:
Obfuscate your Behavior
When manufacturing a firearm, other people will observe your general behavior. The
risks of other people and authorities becoming suspicious of you are manageable
through obfuscation. Obfuscation is the act of obscuring your behavior. It includes
acts which increase your plausible deniability that you are manufacturing a firearm,
and it makes the subject less likely for other people to consider.

Some activities which may help obfuscate your behavior include:

● Find some DIY projects to do. Make home furniture. Make art. Make Christmas
ornaments. Make windchimes. Build a table. Build a shed. It doesn't matter what it is.
Just make some innocuous objects.
● If it is allowed in your jurisdiction, participate in Airsoft or paintball sports. This activity
will enable you to practice your marksmanship and combat skills. Also, it may help
you justify purchases for firearm accessories, like optics and slings.
● If possible, pursue lawful firearm ownership. This may enable you to purchase
ammunition, primers, and propellants, depending on how your jurisdiction regulates
them. If this pursuit may result in unwarranted inspections of your domicile or bring
you under significant scrutiny, please plan accordingly or disregard this idea.
● Don’t be a loner. Clean yourself up and go out. Attend a church, temple, mosque, or
synagogue. Go to the gym. Go to the park. Go to the pub. Join in on athletic events.
Volunteer in your community. It does not matter what you do, as long as it is healthy
and legal. While doing what you decide to do, try to make some real friends. We know
that it is emotionally challenging to have an interest in firearms that you cannot share
with anyone, but you can find other channels of personal connection through genuine
friendships and service to others. Loners live miserable lives. You deserve better.
Machines & Tools
3D Printer & A Thorough Understanding
of How to Use It
Use of a 3D printer takes time and
mastery. Please make sure your printer is
well calibrated and that you understand
how to effectively use it. If you need help
choosing one, we recommend either a
Creality Ender 3 or any Bambu CoreXY
printer. If you choose a Bambu printer, for
privacy, keep it off the internet.

Bench Vise Mounted to a Sturdy

Surface
You will find this important to complete
many of the instructions in this document.

Handheld Drill
You will need this when preparing your bolt
carrier assembly if you do not have access
to a drill press. You will also need this
when preparing your hammer if you do not
have access to a lathe.
 Optional, but Recommended – Chop
Saw, Miter Saw, or Other Tool(s) for
Cutting and Squaring Steel
Chop saws and miter saws are ideal
because they make square cuts a lot
easier. However, they are an investment,
and other, more tedious methods will work.
If you use a chop saw or miter saw, make
sure you use an appropriate cutting disc
for steel.

Optional, but Recommended – Dremel

Tool with Sanding Drums and Steel
Cutting Discs
While you can achieve everything this
would do with cheaper tools, it does make
the heavy lifting on some processes more
efficient. Avoid knockoff brands that make
tools like these, as they are usually junk.

Optional – Drill Press

A handheld drill will work, but you may
prefer to use a drill press when preparing
the bolt core bars. If the arbor is bent on
your drill press, do not use it. (The drill bit
will “wobble” if the arbor is bent.)
 Caliper
You will find this useful this to take
measurements and verify the dimensions
of objects. Quality ones are expensive, but
a worthwhile investment.

Soldering Iron
You will need this to apply brass heatset
inserts to 3D printed, plastic parts.

Needle Nose Pliers

You will need this to prepare your hammer
and cut spring steel wire. You will also find
this helpful for support structure removal.

Hacksaw
You will need this to prepare your bolt and
other metal parts. As you will be cutting
through steel, we recommend having extra
sawblades on hand.
 Medium Grit Sandpaper
You will need this to clean your bolt core
bars before applying JB-Weld

Flat File Suited for Processing Steel

You will need this to process a few small,
metal objects.

Drill Bits of the Following Diameters:

2.1mm, 3.5mm, 5mm, and 6mm
The 2.1mm and 3.5mm drill bits will drill
through steel, so we recommend HSS-Co
M35 or M42 bits. The 5mm and 6mm bits
are only used to ream out plastic parts, so
any drill bit should work.

2.5mm Hex Screwdriver Tool

You can substitute this with a simple hex
key or something more complicated, but
will use it to tighten all the DIN 912 M3
screws that the Urutau requires. There are
a lot of low quality tools out there, so
choose wisely.
Ammunition

Before manufacturing the Urutau, it is critical that you

ensure are able to make or purchase ammunition!
Without ammunition, at best, you creating an Urutau is a
waste of time, money, and effort. At worst, it is a major liability
with no apparent benefit.
By design, the Urutau is intended to chamber 9X19mm
Luger/Parabellum cartridges. There have not been any
attempts at utilizing another cartridge, but be forewarned that
any attempt you make at doing so is highly experimental.

For Americans
In most American states, the sale of ammunition is generally unrestricted. If, for any
reason, you are unwilling, unable, or too autistic to purchase ammunition at a retail
location, online vendors generally do not require a signature or have the mailman
check your identification. Websites like ammoseek.com are great aggregates for
finding the best prices, but on ammoseek.com specifically, don’t order from any
vendors with a shipping score lower than seven.
If you live in a state, territory, or district that controls the sale of ammunition, the
components necessary to load your own cartridges are generally unrestricted. This
includes casings, primers, propellants, and bullets. A cursory internet search of
“reloading 9mm” will provide you with a variety of tutorials on assembling the
cartridges yourself.
For Non-Americans
To begin, please be aware that all ammunition components, casings, bullets, primers,
and propellant are potentially concerning purchases. Please find a way to acquire
these without giving away who you are.
The Hilti loophole is still open in the European Union, and it may be applicable to
other parts of the world. For more information, download ButWhatAbout: Ammo
Volume 1 by IvanTheTroll from The Gatalog.
For those looking to cast lead bullets and electroplate them with copper, download
ButWhatAbout: Ammo Volume 2 by Cathode from The Gatalog.
For those looking to concoct their own primers or those who cannot derive priming
compounds from the Hilti loophole, download Homemade Primer Course by Dr. W.
Marshall Thompson from Aardvark Reloading.
(The website, https://aardvarkreloading.com is accessible via Tor.)
For those looking to concoct their own propellant (powder) or cannot derive propellant
from the Hilti loophole, Gatalog affiliates Albert9x19 and Optimus Synthesis are both
creating separate guides. As of writing, neither of them are in beta yet. If you want
more information, please contact them.
If you are in a country where you cannot find brass casings, vendors in other
countries may be willing to export them to you. Please note that Americans cannot
export ammunition or ammunition components under most circumstances.

The feasibility of all the above recommendations will change as regulators catch up.
But, if innovation continues to outpace regulation, we will have the upper hand. Keep
an eye on The Gatalog and other GunCAD publishers for new innovations as the
status quo shifts.
 Barrel
Manufacturing a quality barrel is the most challenging part of manufacturing an
Urutau, and we recommend making sure you have one before making or printing
any other Urutau components. Similar to ammunition, an Urutau with no barrel is
useless, and it will only be a liability to you if you cannot legally own a firearm.
The barrel of a firearm is a tube which casts a bullet in the direction it is pointed. The
outside may just look simple, but the inside should ideally have a helical pattern of
grooves to impart spin onto the bullet. The reason for this is to stabilize it in flight.
To retain the barrel in the gun, we recommend using three DIN 705 shaft collars with
appropriately-sized set screws. The instructions in the “ECM Barrel” guide explain
how to apply them.

For Americans, we anticipate vendors will manufacture and sell barrels of varying
lengths. However, these vendors will not sell to individuals outside of the USA.

If you are not an American, or if you are, but you want the fun of making your own
barrel, you have options:
1. Create your own barrel with electrochemical machining (ECM). This is the
recommended way to create your own barrel, and all the instructions to do so are
in the “ECM Barrel” directory of the Urutau’s file package. When making a barrel this
way, please make sure you follow all instructions carefully. The process is not hard if
you can follow the instructions, but if you make a serious mistake, you will likely need
to start the process over. By completing the ECM process, you will also test your
ability to utilize your 3D printer, which you will need to print the rest of the Urutau
components after you are finished making your barrel. Note that as part of measuring
the quality of your barrel, you will want to have at least one 9X19mm Luger cartridge
on hand.
2. For expediency, you can utilize a piece of hydraulic tubing, the same kind
recommended in the ECM guide, but with an internal diameter of 9mm and then drill
out the chamber with a 10mm drill bit. The barrel will be extremely inaccurate and
reliability questionable, but at a minimum, it should work. For Americans, if you take
this approach, be aware any firearm with an unrifled barrel is considered a shotgun,
and any shotgun barrel less than 18 inches is considered a short-barreled shotgun
(SBS). Like SBRs, SBSs require registration under the National Firearms Act. Note
that the 18-inch requirement is 2 inches longer than the minimum for a rifle. Given the
inaccuracy of such a weapon, manufacturing the Urutau as an SBS is probably not
worth bothering with, but if you really want to, please review the American Legal
Warning section.
3. If you have access to a quality lathe and are not concerned with potential OpSec
issues, you may machine your barrel from a 9x19mm Luger barrel blank that you can
purchase online. You may need to turn down its OD and chamber it with a 9x19mm
Luger chamber reamer. Unless you trust the precision of your lathe, it is not
recommended to replace the barrel-mounting shaft collars with uncut metal, as any
inaccuracy may lead to headspacing issues. If you are in a legally precarious
circumstance, be aware that a barrel blank and/or chamber reamer would be a
potentially concerning purchase, and it may lead the authorities to investigate you.
Treat this approach with serious caution.
Materials
At Least 2kg of eSun PLA+ or
Polymaker PolyLite PLA Pro
This is what we recommend printing the
gun with. Attempts at using other filaments
are experimental.
NOTE: For the best deal and quality, we
recommend ordering eSun PLA+ from
eSun’s official online store. 10 packs of
filament reels without a spool are the best
deal, and reusable spools are cheap to
print or purchase. Their website is also
very generous with its coupon codes.
30cm or 1ft of 12mm X 20mm or ½” X
¾” Steel Bar Stock
You will make this into your bolt core bars.
We recommend buying more than one in
case the process takes you more than one
try.
6mm Diameter, 250mm Long Stainless
Steel Rods
Two of these rods will become your bolt
guide rods. The bolt’s assembly will also
require a 6mm diameter, 24mm long pin,
which you can cut from one of these rods
or purchase separately
 3mm Diameter, 16mm Long Steel or
Stainless Steel Pins
You will use a pin to add strength to your
hammer. If you have 3mm steel round
stock on hand, you can cut these from it.
As we recommend replacing hammers
relatively frequently, we recommend
keeping many of these on hand.

AR-15 Hammer Spring

CAUTION: THIS IS A POTENTIALLY
CONCERNING PURCHASE. If you are
unable to legally manufacture a firearm,
your billing and shipping information could
lead the authorities to investigate you.
Please follow the instructions to make your
own hammer springs if you cannot buy this
without taking a serious risk.
If you can acquire one, this will become
your hammer spring.

8mm Diameter, 100mm Long Steel or

Stainless Steel Rod
If you cannot acquire an AR-15 hammer
spring, this will become your winding
mandrel for your DIY hammer springs.
3mm Diameter, 20mm to 26.2mm Long
Steel or Stainless Steel Pins
If you cannot acquire an AR-15 hammer
spring, you will use these as part of the
winding jig for your DIY hammer springs.
(25mm ones work great!) If you have 3mm
steel round stock on hand, you can cut
these from it.

1.2mm / 0.045” or 0.047” Spring Steel

Wire
If you cannot acquire an AR-15 hammer
spring, this is the wire you will use to wind
your own hammer springs.

Compression Springs – 8mm Outer

Diameter, 65Mn Steel, At Least 220mm
Long Uncompressed, of the Following
Wire Diameters: 1mm and 0.8mm
You will use these springs for the recoil
system and other parts of the gun. In case
it is not clear, you will need two types of
springs with the same specifications
except for the wire diameter, one type
1mm and the other 0.8mm.
 Compression Spring – 4.5mm Outer
Diameter, 0.5mm Wire OR a Spring from
a Retractable Pen
This will become your firing pin spring
when cut down to 15mm long,
uncompressed.

M3 Brass Heatset Inserts

These will help you secure M3 screws to
the Urutau. 5.7mm x 4.6mm inserts were
the ones we tested with, though slightly
different sizes will probably work just fine.

DIN 912, M3 Screws of the Following

Lengths: 10mm, 16mm, 20mm, 40mm
You will primarily use these to hold your
gun together. When this document refers
to M3X#mm screws, you can assume they
are DIN 912. These screws are very useful
in more than just the Urutau, so we
recommend keeping many on hand.
5mm Diameter, M3 Threaded Spacers of
the Following Lengths: 10mm and
25mm, At Least 10 Each
You will use these primarily to assemble
the fire control group.
While these have many plausible, legal
uses, we are concerned that the only place
to purchase these is AliExpress. If these
ever become unavailable, or if you really
want to cover your tracks, look in the
alternative files section for a solution which
replaces these with brass heatset inserts
and 5mm diameter, 40mm long steel pins.
DIN 933, M5 Screws with a Length
Greater Than or Equal to 11.6mm
You will use these to reinforce your
hammer in the area where it contacts the
tail-end of your firing pin. As we
recommend replacing hammers relatively
frequently, we recommend keeping many
of these on hand.

623ZZ Ball Bearings

You will use two of these for your charging
handle.
 JB-Weld
You will use this to bond metal parts to
other metal or plastic parts.

Superglue (Cyanoacrylate)
You will use this to link the two safety bars
together.

Oil for Drilling Steel

You will use this to keep your drill bits cool
and prevent seizing when drilling steel
parts.

Isopropyl Alcohol
You will use this to clean your bolt core
bars before applying JB-Weld to them.
 DIN 705, 3mm ID, 7mm OD, 5mm Long
Shaft Collar
You will use this to make your firing pin.

1.5mm Hex Driver Shaft

You will use this to make your firing pin.
While these have many plausible, legal
uses, we are concerned that the design is
dependent on the particular shape of this
item. Likewise, purchasing this item may
leave you vulnerable to correlation attacks.
If these ever become unavailable, or if you
really want to cover your tracks, look in the
alternative files section for a solution which
replaces this item with an M4 screw.
Extended Glock Magazine Springs
CAUTION: THIS IS A POTENTIALLY
CONCERNING PURCHASE. If you are
unable to legally manufacture a firearm,
your billing and shipping information could
lead the authorities to investigate you.
Solutions exist to wind your own, but they
have not yet been tested to Gatalog
standards.
You will use these to make your
magazines.
 Chemical(s) to Clean, Lubricate, and
Prevent Rust
Ballistol is often a preferred choice due to
its versatility. However, it and other firearm
cleaning solutions may be a concerning
purchase in serious conditions. As an
alternative, WD-40 Corrosion Inhibitor may
be useful on your barrel and exposed
metal parts of your bolt, and synthetic
motor oil or graphite powder may be useful
as a lubricant for moving parts.

Optional – M3 T-Nuts
If you would like to use the M-LOK sling
mount or other M-LOK accessories, you
will need these to mount them to the barrel
cover.

Optional – Firearm Sling

CAUTION: THIS IS A POTENTIALLY
CONCERNING PURCHASE. If you are
unable to legally manufacture a firearm,
your billing and shipping information could
lead the authorities to investigate you. As
an alternative, you can substitute this with
just about any “suitcase strap” for sale.
If you would like to carry your firearm, this
will help you keep your hands free.
3D Printed Parts
The purpose of this section is to provide generic guidance on the best way to print all
of the Urutau’s plastic pieces. Anything we do not specify is up to your best judgment.
You know your 3D printer better than we do, so unless you are new to 3D printing,
your intuition takes precedence.

Nozzle Temperature: 215-220°C

Bed Temperature: 60°C (35°C for Bambu Printers with a Cold Plate)
Layer Height: 0.16mm
Infill: 100% Rectilinear
Bambu Printers: Maximum Volumetric Speed should be less than or equal to 6mm/s
Orientation, Brim, & Supports: As specified for each part.

Hammer
Use supports on the build plate only. This
may cause some plastic to sag in the
screw cavity, but this is expected.
We listed this piece first as the hammer
requires JB-Weld to finish.
 Bolt Carrier Housing
Use supports on the build plate only.
Support cleanup will be a little tricky on
this one. Use of a brim is recommended.
We listed this piece second as the bolt
requires JB-Weld to finish.
Based on whether your steel bar stock is
12mm X 20mm or ½” X ¾”, print the metric
or imperial version, respectively.

Lower Receiver
If you are able to do support painting,
apply supports only to the downward-
facing, planar surfaces. If not, simply use
supports everywhere. Use of a brim is
recommended.
You are welcome to try lying this down so
that the sling loop is pointing upward, but
that orientation is vulnerable to warping.
 Rear Cap
No need for supports. Printing with a brim
is recommended to prevent warping.
If you are an American trying to avoid
manufacturing a short-barreled rifle (SBR),
please make sure you print the extended-
length version to meet legal overall length
requirements.

Upper Receiver
Supports are only required in the area that
contacts the barrel, highlighted below.

Supports in the ejection window may

improve appearance, but are not required.
They are not needed anywhere else. Use
of a brim is recommended.
 Grip
Tree supports are recommended to get the
best surface finish, though normal support
structures will work too. If you understand
the limits and capabilities of your printer,
you may use support painting to cover only
the areas where need support the most.
Use of a brim is recommended.

Barrel Retainer
No supports are necessary. Use of a brim
is recommended.
 Barrel Cover
No supports are necessary. Use of a brim
is recommended.

Ejector
No supports are necessary.
 Feed Ramp
No supports are necessary.

Hammer Spring Winder

Only print this part if you need to wind your
own hammer springs. No supports are
necessary.

Hammer Spring Winder Vise Piece

Only print this part if you need to wind your
own hammer springs. No supports are
necessary.

Hammer Spring Winder Knob

Only print this part if you need to wind your
own hammer springs. No supports are
necessary.
 Fire Control Group Housing
Use supports everywhere applicable.

Disconnector
Use supports on build plate only.
 Trigger
No supports are necessary.

Trigger Bar
No supports are necessary.

Safety Drum
No supports are necessary.

Safety Locking Peg

Print this twice. Supports may create a
nicer finish, but given the small size of the
cantilevered area, they may not be worth
bothering with.
 Rear Safety Bar
Use supports where applicable. They are
only required in one small area.

Front Safety Bar

No supports are necessary.

Magazine Release
No supports are necessary.

Charging Handle Adaptor

No supports are necessary. There is a little
bridging on this piece, but most printers
are able to make it without supports.
 Charging Handle
Use supports on build plate only. Print this
twice if you want to make an ambidextrous
charging handle.

Charging Handle Cap

No supports are necessary. Do not print
this if you want to make an ambidextrous
charging handle.

Locking Tab
No supports are necessary, unless you
really care about the inside finish of the
spring cavity.

Locking Tab Knob

Use supports on build plate only. Print this
twice.
 Magazine Body
No supports are necessary. Print one of
these for as many magazines as you
would like, though be aware of potential
cumulative consequences if you are in a
legally precarious circumstance.

Magazine Follower
Use supports on build plate only. Print one
of these for each magazine you want to
make.

Magazine Lock Plate

No supports are necessary. Print one of
these for each magazine you want to
make.

Magazine Base Plate

No supports are necessary. Print one of
these for each magazine you want to
make.
 NATO Rail
No supports are necessary. Use of a brim
is recommended.

Butt Pad
No supports are necessary. If you have
TPU on hand, you may use it for this part.
If not, PLA works just fine.
Your Urutau will function without this piece,
but shouldering it may become more
difficult and/or uncomfortable.

Brass Deflector
Depending on your printer’s bridging
abilities, supports are optional.
Your Urutau will function without this piece,
but it is intended to keep discarded brass
from hitting you in the face.
 Cheek Raiser
No supports are necessary, unless you
want a slightly higher-quality finish.
Your Urutau will function without this piece,
but it exists for your comfort.

Sling Mount
No supports are necessary. Print this only
if you want an external mount for a sling.
Your Urutau will function without this piece.

Grip – Lower Receiver Shim

You may need this if you have a higher
end or well calibrated 3D printer, as the
grip and lower receiver have a small gap
to compensate for potential printing
inaccuracies.

Barrel Retainer Shim

You may need this as the barrel retainer
has a little extra room in case of slightly
overlength shaft collars.
 Bolt Pinning Jig
No supports are necessary. You will want
to make a new one for each set of bolt
core bars you process. Based on whether
your steel bar stock is 12mm X 20mm or
½” X ¾”, print the metric or imperial
version, respectively.

Bolt Face Drilling Jig – Channel Piece

No supports are necessary. You will want
to make a new one for each bolt face you
process. Based on whether your steel bar
stock is 12mm X 20mm or ½” X ¾”, print
the metric or imperial version, respectively.

Bolt Face Drilling Jig – Retainer Piece

No supports are necessary. You will want
to make a new one for each bolt face you
process. Based on whether your steel bar
stock is 12mm X 20mm or ½” X ¾”, print
the metric or imperial version, respectively.
If you already have an optic or sight system that you would prefer to use, you can skip
the rest of this section. If not, continue on.

Front Sight Body

No supports are necessary.

Rear Sight Body

No supports are necessary.

Front Sight Clamp

No supports are necessary. At your
discretion, different orientations will work
when printing this piece.
 Rear Sight Clamp
No supports are necessary. At your
discretion, different orientations will work
when printing this piece.

Sight Drum
No supports are necessary.

Drum Locking Piece

No supports are necessary.

Rear Sight Locking Tab

No supports are necessary.

Locking Tab Locking Piece

No supports are necessary.
 Bolt Carrier Assembly
1. Start by cutting a 26mm length of your 12mm
X 20mm or ½” X ¾” steel bar stock. Yes, it will
need to be 26mm long whether you are using
metric or imperial steel bar. We don’t have the
time or resources to test a bunch of out-of-
spec bolt pieces to tell you what will and won’t
work, but please make the cut as square as
you can and length as precise as you can.

2. Insert the steel piece you cut into the bolt face
drilling jig, and then fit the jig together. The
pieces are purposely designed to fit very
tightly, and you may find a bench vise useful
to press them together.

3. If one side of the metal bar is squared worse than the other, choose a set of holes on
that side. (You will be cutting away most of that side to make the cartridge pickup
anyway.) We recommend drilling the smaller hole first, as precision is more important
when drilling the smaller hole, and heat generated when drilling the larger holes may
warp the jig. We also recommend applying a few drops of cutting oil into the channels
before drilling. A drill press is helpful for this step, but if you do not have one, a
handheld drill will work. Mount the jig to a vise, then drill through the smaller hole with
a 2.1mm drill bit and the larger holes with a 3.5mm drill bit. When drilling, pause
occasionally and remove the bit to clear chips out of the channel.
4. After you completely drilled through all three holes,
mount the assembly to a vise and use a punch, hex key,
or other sturdy tool to remove the metal bar from the jig.

5. With a hacksaw, cut the metal as depicted. You are

welcome to use a more powerful tool, but we believe a
hacksaw is the easiest to control. It may come out jagged
and ugly, but we will clean it up in the next step.

6. Use a Dremel tool with a sanding disc and a file to

process the metal piece until it appears as depicted. Only
use the Dremel tool for the heavy lifting. If you don’t have
one, you can complete this step of the process with only
a file.
7. Test fit the bolt face you made by fitting it in a bolt carrier
housing. The depicted surfaces should be flush. If you
insert the 1.5mm hex driver shaft that you will make into
your firing pin, it should glide in and out with little to no
resistance.

8. Cut a 27cm length of your 12mm X 20mm or ½” X ¾” steel bar stock. Yes, it will need
to be 27cm long whether you are using metric or imperial steel bar. Please make the
cut as square as you can and length as precise as you can. It is okay if you cut it a
little short, but if it is too long, it will not work.

9. Insert the piece you just cut and the bolt face into the pinning jig. Make sure they are
fully inserted.
10. With a 6mm drill bit, drill 29mm deep, including the
face of the jig. This will make a 24mm deep hole
through both metal pieces. A drill press is helpful for
this step, but if you do not have one, a handheld drill
will work. Apply a few drops of cutting oil before
drilling and remove the bit occasionally to clear out
chips.

11. Remove the metal pieces from the jig. You may need to use a rod and hammer to
knock them out. Make sure the holes you drilled are clear of debris and insert a 24mm
long, 6mm diameter steel pin through both holes.

12. Test fitting the assembly by inserting it into your bolt carrier housing. You will want to
make sure that the metal bolt face is flush with the plastic.
13. Remove the bolt core bars from the bolt carrier housing. To make sure they remain
secure in the bolt carrier housing, we will need to thoroughly clean the surfaces that
you will cover with adhesives. With medium-grit sandpaper, scratch inward-facing
surfaces in a criss-cross pattern, but not the front or rear face of the piece containing
the firing pin channel.

14. Clean the surfaces you just scratched with isopropyl alcohol. Carry on once the
surfaces are dry. (Pausing here is a bad idea as the surfaces may rust if left exposed
to the air.)
15. Mix a little JB-Weld, twice the same amount of toothpaste you would use to brush
your teeth. Apply it thinly to the surfaces you scratched with sandpaper. Then, insert
the bolt core bars fully into the bolt carrier housing. Make certain that there is no
JB-Weld in the firing pin channel! If there is, clean it out.
16. The JB-Weld will fully cure after 24 hours. It should be dry to the touch after 8 hours,
and you may continue the assembly process past that point. However, do not charge
or fire the Urutau until after 24 hours passed.
17. While waiting on the bolt carrier assembly, you can prepare your firing pin. Take a
1.5mm RC hex driver and cut the tip down to make it 94.5 mm long. A Dremel tool
with a cutting disc is ideal for this, but any cutting tool will work. Using a file or a
Dremel tool with a sanding disc, cut a conic or dome shape into the tip of the firing
pin. It doesn’t have to be perfect, but we want to minimize any sharp edges.

18. Using a Dremel tool with a cutting disc or other appropriate tool, 10mm from the tail
end of the firing pin, cut a notch or divot into the flat surface. This may or may not be
the exact middle of the flat surface, depending on the manufacturer of the driver shaft.

19. Mix a drop of JB-Weld and apply it to the

notch or divot you cut. Apply a DIN 705 3mm
ID shaft collar and slide it so the grub screw is
over the notch. You may need to loosen the
grub screw to do this, but be careful not to
lose it. Once the grub screw is positioned over
the notch, tighten it hard, and then pull the
shaft collar both directions to make sure that it
does not move. If it moves, reposition the
shaft collar then try again. If not, apply
another drop of JB-Weld to the outside of the
grub screw channel so it will not back out.
20. The JB-Weld will fully cure after 24 hours. It should be dry to the touch after 8 hours.
However, do not dry or live fire the Urutau until after 24 hours passed.

21. With a soldering iron, apply an M3 brass insert as depicted.

22. Cut a 15mm (uncompressed) piece from your

4.5mm OD, 0.5mm wire spring. This will become
your firing pin spring.

23. The JB-Weld should be dry to the touch before competing this step and continuing on.
Apply the firing pin spring spring to your firing pin assembly.

24. Insert your firing pin assembly into the bolt carrier assembly. It should enter smoothly
with little to no resistance.
If you feel the firing pin seize up
or stop ~12mm before it is fully
inserted, your steel firing pin
channel is not aligned properly or
it is obstructed by JB-Weld.
25. While pressing the firing pin into place, apply an
M3X20mm screw as depicted. Note that this will not
occupy the entire width of the bolt carrier housing,
but as long as it retains the firing pin, that is okay.
(If you would prefer to use a slightly longer screw,
that is also okay as long as it does not protrude out
the side of the housing.)

26. Check the protrusion of your firing pin by pressing it

down completely like you did in the last step. It
should protrude between 1mm to 2mm. If it is
longer, trim it down slightly, as this creates a risk of
out-of-battery detonations and pierced primers. If it
is shorter, you will need to create a new one, as the
gun may not detonate the cartridges reliably.

27. Lubricate two separate, Ø6X250mm stainless steel rods and insert them into the
guide rod channels on your bolt carrier. They should glide in and around smoothly. If
they don’t, hand-ream the channels with a 6mm drill bit or reamer. Set the guide rods
aside until it is time for the rear cap assembly.
The creation of your bolt carrier assembly is complete! Set it aside until it comes time
for the final assembly of the Urutau.
 Hammer Spring Winding
If you already own or are able to safely acquire an AR-15 hammer spring, skip this
section. If not, the following steps will guide you through winding a hammer spring.
Special thanks to ImmortalRevolt for sharing his winding jig prototype with us!

1. Make sure you have two 3mm diameter steel pins that are between 20mm and
26.2mm long. Insert them into the winder and vise piece so that 1.2mm of the pin
protrudes from the channel. It doesn’t have to be perfect, but you may find a caliper
helpful for this step.

2. Optionally, use a soldering iron to apply an M3 brass insert into the winder knob, and
then use an M3X10mm screw to attach it to the winder. This is a matter of personal
preference, and the winding jig will function just fine without it.
3. Insert your 8mm diameter stainless steel rod, the winding mandrel, into the mandrel
channel in the winder.

4. Mount the vise piece in a bench vise (not pictured) and insert the other end of the
winding mandrel into its channel.

5. Insert your 1.2mm / 0.045”-0.047”

spring steel wire between the
winding mandrel and 3mm wire
catch pin in the vise piece.
6. Press the winder and mandrel downward so its protruding wire catch
pin presses the wire against the mandrel. You may need to bend the
wire slightly to do this, and that is okay.

7. Your goal is to wind the wire into

four loops, one on top of the other,
with each of the legs a 180° angle
to each other, as depicted. With
the wire fixed in place, press down
on the winder and slowly rotate it.
The wire will uncoil slightly when
you release the winder, so you will
need to rotate the winder a little
more than four times to create a
180° angle.

8. When the coils are wound, cut the spring. You will want one leg around 33mm long
and the other around 17.5mm long. It doesn’t have to be perfect, but it is easier to cut
a little more later than it is to start over.

9. Repeat this process from step 5 onward to create your other hammer spring. You will
need to wind it in the opposite direction of the spring you just made. You may find
reversing the direction of your vise piece in your bench vise helpful in doing so.

The creation of your hammer springs is complete! Set them aside until reaching step
10 of the lower assembly process.
 Lower Assembly
1. Chuck a DIN 933 M5 hex-head screw into a drill. Spin the drill and use a file to round-
off the hex shape. Generally, you want the diameter of the rounded head of the screw
around 8mm, but a good way to test this is to insert the head of the screw into the
cavity in the hammer. If it feels stiff going in, file a bit longer and try again. If not,
remove it and continue on.

2. Cut the screw down to no longer than an 11.6mm overall length. If it

is a little under, that is okay, but it cannot be longer than 11.6mm.
Deburr any rough edges with your file.

3. Make sure you have a 3mm diameter, 16mm long steel dowel pin on hand. If it is a
little shorter than 16mm, that is okay, but if it is longer, please cut and/or file it down.
4. Using an uncut M5 screw, insert the threaded
end into the channel and rotate it out again. This
is optional, but it will make the next few steps
easier. Do not overtighten, as that will strip the
channel of its ability to catch the screw.

5. Apply drops of JB-Weld into the hammer’s screw

cavity and the channel inside the hammer’s
wings.

6. Insert the 16mm long steel dowel pin as

depicted. You may find a hammer or bench vise
useful for tapping or pressing it into place. Also
insert the cut and rounded M5 screw as depicted.
You will find a pair of pliers useful for this step.
You will not be able to get it all the way in, but try
to get it as deep as you can. Wipe away any
excess JB-Weld that oozes out.

7. Assuming you are working at room temperature, give the JB-Weld 24 hours to cure. It
should be dry to the touch after 8 hours, so you may continue the assembly process
past that point, but do not dry fire or live fire the Urutau until 24 hours are passed.
8. Use a file to grind the face of the screw flush with the
hammer. Though it is unavoidable, try to avoid
damaging the plastic as best you can.

Whereas the hammer takes more than 24 hours to prepare and requires occasional
replacement, we recommend making more than one, provided that you have a good
hiding location if you are in a legally precarious situation.

9. Place 7.5 coils of your 8mm OD, 0.8mm wire

compression spring stock into its cavity on the fire
control group housing floor. Place the
disconnector on top of it. Insert a Ø5X25mm M3
threaded spacer. You will need to resist the
disconnector spring pressure to insert the spacer,
but it should not take too much physical effort. If
you have difficulty inserting the spacer, ream the
disconnector’s channel with a 5mm drill bit.

10. Apply your hammer spring(s) to the hammer as depicted. If you get this wrong, your
Urutau will not fire reliably.

DIY AR-15
11. Insert a Ø5X25mm M3 threaded spacer
as depicted. Be aware that it will want to
fall out until the completion of the next
step.

12. Place the legs of the hammer spring(s) onto the spacer you just inserted. Then, press
the hammer down until its channel aligns with the opening in the fire control group
housing. Insert another Ø5X25mm M3 threaded spacer as depicted when it is
aligned. Cock the hammer once the spacer is in place. If you have difficulty inserting
the spacer, ream the hammer’s channel with a 5mm drill bit.
13. Insert 5.5 coils of your 8mm OD, 1mm wire compression spring stock into the cavity in
the fire control group housing. Be aware that it will want to fall out until the completion
of the next step.

14. Insert the assembled fire control

group cassette into the lower
receiver. This step will be a little
tricky, as you will need to fight the
fire control group housing spring,
and the sharp end will want to
catch the plastic. Make sure that it
does not get bent out of shape.
15. Apply M3X16mm screws into the holes
as depicted. Do not overtighten, as
doing so may warp the lower receiver
and hinder the function of the fire
control group. If you need to push the
fire control group components around,
be ready to catch the hammer in case
you accidentally release it. (Getting
unexpectedly smacked by it hurts.)

16. Insert a Ø5X25mm M3 threaded spacer into your safety drum.

17. Insert your drum into the lower receiver, and then
apply two M3X16mm screws into the holes as
depicted. Again, do not overtighten. Do not worry
about the orientation of the drum just yet.

18. With a soldering iron, apply M3 brass heatset inserts into the lower receiver and grip
as depicted.

19. Install the feed ramp into the lower receiver

with an M3X16mm screw.
20. Test the fit of your grip on the lower receiver by placing the two parts together.

If you see a discrepancy as depicted in the image, you will

need to use the grip-lower shim. This is probably because
you are using a higher end or well-calibrated 3D printer.

21. If you need to use the grip-lower

shim, drop it into place. Fit the grip
into the lower receiver and secure it
in place with an M3X10mm and
M3X16mm screw.
22. Insert a Ø5X10mm M3 threaded spacer
into the channel on the trigger.If you have
difficulty inserting the spacer, ream the
trigger’s channel with a 5mm drill bit.

23. Insert the trigger into the grip as depicted,

and then use two M3X10mm screws to
secure it in place.

24. Cut 4 coils of your 8mm OD, 0.8mm wire

spring. Insert the safety locking pegs into
the front safety bar so they protrude out
their channels. Then, insert the cut spring
to pin them into position.

25. Use a drop of superglue to attach the two safety bars together. Once it is cured, use
sandpaper to clean up any glue that oozed out.
26. Orient your safety drum so the flat face is
facing away from the grip, toward the rear
of your lower receiver. This is the position
we what the drum to be when the safety
switch is in the forward (1 / fire) position.

27. Without rotating the safety drum, drop the safety bar into the forward position.

28. Drop the trigger bar into place. Be aware that from this point forward, pulling the
trigger will release the hammer.
29. Cut 4 coils from your 8mm OD, 1mm wire
spring. Insert a Ø5X25mm M3 threaded
spacer into the channel in the magazine
release, and apply the cut spring to the cavity
as depicted. If you have difficulty inserting the
spacer, ream the magazine release’s channel
with a 5mm drill bit.

30. Insert the magazine release into the lower

receiver and align the spacer with the
screw channels. Secure it into place with
two M3X16mm screws. You will need to
fight the spring pressure until the screws
are at least partially installed.

The assembly of your Urutau lower is now complete! Set it aside until it comes time
for the final assembly.
 Rear Cap Assembly
1. With a soldering iron, apply M3 brass inserts to
the locking tab as depicted.

2. Cut 7.5 coils of your 8mm OD, 0.8mm wire

spring. Line up the spring with the cavity on the
locking tab, and insert them both into the rear
cap. You will need to hold the tab down until the
completion of the next step.

3. Secure the locking tab knobs to the locking tab

through the rear cap with two M3X16mm screws.
4. To create a functional firearm, this step
and step 5 are recommended, but
optional. (Skipping them will make
shouldering your weapon a bit more
uncomfortable and slippery.) With a
soldering iron, apply M3 brass inserts to
the rear cap as depicted.

5. Secure the butt pad to the rear cap with

two M3X16mm screws.

6. Insert six M3X20mm screws into their

respective holes on the rear cap, making
sure they are clear of print debris. This
may seem unimportant, but you will be
fighting a lot of spring pressure when you
install the rear cap to the upper receiver
later in these instructions, and you will find
having the screws in position helpful.
7. Make sure you have an upper receiver on hand. (It
does not need to have had any post-processing done
on it yet.) Apply drops of JB-Weld into the guide rod
cavities in the rear cap. Then, insert your guide rods
into the upper receiver and align the upper receiver
with the rear cap. (Screwing anything down is not
necessary.) With a mallet or blunt object, tap the guide
rods into the cavities. Lie the rear cap down so the guide rods and upper receiver
point up. Make sure the upper receiver is aligned one last time, and then give the JB-
Weld 24 hours to cure.

For context, the only reason we require this step

is to significantly simplify the final assembly
process. The guide rods will have a hard stop
going in both directions when the firearm is fully
assembled. In other words, the JB-Weld will not
be responsible for holding anything together
once the firearm is fully assembled.
The assembly of your rear cap is complete! Set it aside until it comes time for the final
assembly.
 Upper Assembly
1. With a soldering iron, apply M3 brass inserts to the upper receiver as depicted.

2. Insert the ejector into the upper receiver.

3. Apply an M3X20mm screw into the upper receiver

through the ejector. You may need to carefully
position the ejector so the screw slides through its
channel.
4. With a soldering iron, apply M3 brass
inserts to the barrel retainer as depicted.

5. Insert your barrel and its shaft collars into the barrel retainer. The instructions to apply
the shaft collars are in the ECM guide if you have not already.

6. Secure the barrel retainer and barrel to the upper receiver with four M3X40mm
screws.
7. Try twisting and pulling your barrel as it is installed in the upper receiver and barrel
retainer. If it feels sturdy, continue on to step 8. If you feel it move around, you will
need to apply a shim to the inside of your barrel retainer to keep it held tightly in
place. Remove the M3X40mm screws and barrel retainer from the upper receiver,
and then remove the barrel from the barrel retainer. Apply the barrel retainer shim
onto the barrel as depicted, and then continue from step 5.

8. With a soldering iron, apply M3 brass

inserts to the barrel cover as depicted.

9. Attach the barrel cover to the barrel retainer with an M3X16mm screw as depicted.
10. With the barrel cover fully inserted, insert two M3X10mm screws as depicted.

11. With a soldering iron, apply M3 brass inserts to the

charging handle adaptor as depicted.

12. Use two M3X10mm screws to secure two 623ZZ ball

bearings to the charging handle adaptor as depicted.
They should be snug, but do not overtighten. After
securing the screws down, make sure the ball
bearings rotate freely.

13. Insert the charging handle adaptor into the barrel cover.
14. While making sure your charging handle adaptor is aligned
properly, use an M3X40mm screw to secure your charging
handle to the charging handle adaptor through the slot in your
barrel cover. If you want a charging handle on both sides, do
the same on the other side. If not, use an M3X20mm screw to
secure the charging handle cap to the other side.

15. Secure the NATO rail to the upper assembly with ten M3X10mm screws.

16. Secure the brass deflector to the upper

receiver with two M3X10mm screws.
This is optional, but it will minimize the
chances of brass hitting you in the face.
17. Secure the cheek raiser to the upper receiver with
four M3X10mm screws. This is optional, but it will
add comfort when aiming the gun. You can adjust
its height as needed at any point in the future.

The assembly of your Urutau upper is now complete! Set it aside until it comes time
for the final assembly.
 Iron Sights
If you already have an optic or sight system that you would prefer to use, skip this
section. If not, we strongly recommend following the instructions in this section to
make sure that you are able to aim your Urutau effectively.
1. With a soldering iron, apply M3 brass inserts to the sight bodies as depicted.

2. Cut 5.5 coils from your 8mm OD, 0.8mm wire spring. Insert the spring into its cavity in
the rear sight body and press it down with the rear sight locking tab. Hold it down until
you finish step 3.
3. Secure the locking tab
locking piece into place
with an M3X10mm screw.
This should keep the
locking tab and its spring
from falling out.

4. Use an M3X10mm screw and

your drum locking piece to
secure the rear drum into place.

5. Test the drum by rotating it. It should lock

into place in two positions.
6. Apply the sights to the NATO rail with their sight clamps and M3X40mm screws. If you
need to disassemble the upper receiver at any point in the future, you will need to
remove at least some of the screws that attach the NATO rail to the rest of the upper,
so you may choose to delay the completion of this step to any point between now and
firing the Urutau for the first time.

When using the open side of the rear drum, it should be accurate to 50 meters. When
using the circular side, it should be accurate to 25 and 95 meters.

50 Meters 25 & 95 Meters

 Magazine Assembly
The following steps will walk you through the assembly of the Urutau’s magazine. If
you live in an area where 30-round magazines are prohibited, we recommend saving
this step for last as it is quick, easy, and has a low likelihood of failure.

1. Apply the follower to the smaller coils of the magazine spring. There isn’t much to
hold it in place, so make sure it does not fall off before completing step 2.

2. Insert the spring and follower into the magazine body as far as it will go.

3. Press the magazine lock plate into the

protruding spring and into the magazine.
Then, slide the magazine base plate into
place. It should fit tight, and you may need
a hammer to tap it into place.
4. Make sure the peg on the magazine lock plate fell into
the hole in the magazine base plate. If not, push it around
until it does.

5. This step is optional, but ensures the quality of your magazine

by dry-cycling it. Insert 30 rounds into the magazine and then
push them all out with your thumb. If they all come up from
the magazine without hesitation, your magazine should be
good to go!

Repeat this process for as many magazines as you

would like, though, again, be aware of potential
cumulative consequences if you are in a legally
precarious circumstance.
 Final Assembly

1. Cut two separate 220mm (uncompressed) lengths of your 65mn, 8mm OD, 1mm wire
spring. Apply the springs to the guide rods.

2. Drop the bolt carrier assembly into the upper receiver. You will need to make sure the
tail-end of the ejector is out of the way when doing so.
3. This step will be tricky. Insert your guide rods into the channels in the bolt carrier
assembly. Push down on the rear cap with one hand so that the rods go through the
channels in the bolt carrier assembly and upper receiver. With the rear cap flat
against the surface of the upper receiver, screw at least one of the M3X20mm screws
into place. Past this point, you don’t need to hold the rear cap assembly in place, but
please screw the remaining M3X20mm screws tightly. From testing, the Urutau only
needs two screws in place for the it to function, but for safety reasons, we recommend
utilizing all six.

4. Insert a Ø5X25mm M3 threaded spacer into the barrel cover as depicted. Use a 5mm
drill bit to ream out the hole if the spacer is too difficult to insert.
5. With the spacer inserted into the barrel cover,
insert that spacer into its position in the grip.
Use two M3X16mm screws to attach the grip
to the barrel cover.

6. Pivot the gun closed. The locking tab should click

into place.

7. Optionally, if you would like to

attach a sling, use an M3 T-Nut
and M3X10mm screw to attach
the sling mount.
8. Inside the thumbhole, apply an M3X10mm
screw to hold the gun together. This is
optional but recommended.
The reason we recommend inserting this
screw is that the upper and lower will split
when a loaded magazine is inserted,
possibly resulting in feeding issues. If your
gun feeds okay without it, then it shouldn’t
be necessary.

9. Optionally, insert a magazine

and admire your hard work!
The assembly of your Urutau is now complete!
 Function Testing
Dry Firing
1. Make sure there is no magazine in the gun. Pull the charging handle back as far as it
will go, and look inside the chamber to make sure it is empty. Release the charging
handle. The bolt should come forward quickly and make a loud “smack” sound. If it
does not, your gun will not cycle. In such a case, please check your recoil springs and
guide rods that they are clean, lubed, and fit properly.
2. Insert a magazine into the magazine well. The magazine release should make a
“click” sound when the magazine is locked into place. When the magazine is locked
into place, pull down on the magazine. It should not come out. If it comes out, it was
either not inserted completely or there is something wrong with the magazine release.
Push the magazine release forward and pull down on the magazine. The magazine
should come out of the gun. It may feel a little stiff coming in and out, but it will
become easier as the magazine breaks in. If this test fails, make sure your magazine
release is installed correctly and that nothing is obstructing the magazine.
3. Move your safety switch to the rear position (0 / safe) if it is not there already. Try
pulling the trigger. The trigger should feel stiff, and nothing should happen. If the
hammer is released, check that your safety drum is clocked appropriately. The flat
face should point toward the front of the gun when the safety switch is in the rear
position. If it is not, adjust it accordingly.
4. Move your safety switch to the forward position (1 / fire). Try pulling the trigger. The
hammer should release, making an audible “click” sound. If it does not, make sure
that your fire control group housing spring is aligned properly, and check that the flat
face on your safety drum is pointing toward the rear of the gun when the safety is in
the forward position. If the hammer successfully released when pulling the trigger,
hold the trigger down, pull the charging handle back as far as it will go, release the
charging handle, and then release the trigger. When you release the trigger, the
trigger should spring forward, and you should hear another audible “click” sound. If no
sound is audible, check the inside of the gun to see if the hammer is still attached to
the disconnector. If it is, you may need a stronger fire control group housing spring.
 Live Firing

1. Load a magazine with as many cartridges

as you want. Insert the magazine into the
magazine well.

2. Pull the charging handle back as far as it

will go and release it. Check that the bolt
went into battery by making sure that the
arrows appear in the ejection window as
depicted.

3. Move your safety switch to the forward

position (1 / fire).

4. Pull the trigger. The gun should go off with each trigger pull. Repeat this process until
you are satisfied.
 Maintenance
Like all firearms, the Urutau will need maintenance after use or long-term storage.
While its beta testers fired a collective couple thousand rounds through the gun, we
do not have the time or resources to test it further. For this reason, this section is
intended to provide shorter-term maintenance advice, some from experience, and
some speculative. Common sense should take precedence.
1. Inspect your magazine feed lips for cracking when loading them. Cracked feed lips
may result in double feeding from the magazine. From experience, it is difficult to tell
how much use a magazine can take before this happens, but replace the magazine
body if its lips appear cracked.
2. Inspect your fire control group components, your hammer especially, every 300
rounds. The surface of your hammer that contacts the bolt carrier housing when
cycling will wear out the fastest. From testing, the fire control group components will
likely survive much more than 300 rounds if printed correctly. However, if reliability is
critical and you have the resources to do so, replace the printed fire control group
components, or at minimum, the hammer, every 300 rounds.
3. Clean and lube your firing pin after shooting or after leaving your Urutau in storage for
a while. Your firing pin will become covered in debris after shooting. If too much debris
accumulates, your firing pin may seize up. It is not clear from testing how much it
takes for this to happen, but we recommend cleaning and lubricating your firing pin
after shooting when possible.
4. Clean and lube your guide rods every 300 rounds or after leaving your Urutau in
storage for a while. Debris accumulation occurs more slowly on the guide rods than
the firing pin, but poorly lubricated guide rods will cause feeding issues.
5. Periodically inspect the bottom of your bolt carrier housing where it contacts the
hammer. This area will also become worn more quickly due to the friction it has to
endure. We don’t know at what point it may start to cause issues, but replace the bolt
carrier housing if it appears significantly worn.
Troubleshooting
Hammer does not release on trigger pull.
1. Make sure the fire control group housing spring is not bent up.
2. Make sure the fire control group screws are installed.
3. Make sure the fire control group screws are not overtightened.
Hammer does not reset when releasing the trigger.
1. Experiment with a stronger fire control group spring.
2. Remove the fire control group and clean any debris in the lower receiver’s floor.
3. Make sure the fire control group screws are not overtightened.
Cartridges fail to feed.
1. Ensure the screw between your grip and barrel retainer is reasonably tight and
still in place.
2. Make sure your guide rods are clean and lubed.
3. Dry cycle your magazine to ensure that it is cycling properly. This is especially
important if you are using a DIY magazine spring.
4. Experiment with stronger recoil springs.
Casings fail to eject.
1. Ensure the ejector is not significantly worn.
2. Ensure there is nothing blocking the ejection port.
The case head is separating, leaving part of the casing in the chamber.
1. Your headspacing is probably too shallow, meaning that your bolt is slamming
the cartridge deeper into the chamber than it can go. Check the barrel with the
headspacing gauge in the ECM directory.
2. The ammunition may have been made by sloppy reloading or with low-quality
brass.
The firing pin strikes the primer too lightly for it to detonate.
1. Make sure your firing pin is clean and lubed. Too much debris accumulation on
the firing pin will cause it to seize up.
2. Your headspacing may be too deep, meaning that your cartridge has some
wiggle room when the gun is in battery. Check the barrel with the headspacing
gauge in the ECM directory.
3. The ammunition may have been made with low-quality or stubborn primers.
Trigger pull feels crunchy.
1. If the gun has been fired, remove the fire control group and clean any debris in
the lower receiver’s floor.
2. If the gun is relatively new, break it in by dry-firing.
Trigger pull is too heavy.
1. You may experiment with a lighter fire control group housing spring, but that
may result in hammer reset failures.
2. Grow some muscles, weakling!
Technical Aspects and Design Choices
The purpose of this section is to provide contextual information that explains the
rationale behind the design choices made for the Urutau. While understanding this
information is not essential to manufacture the Urutau, we believe that readers will
find it enlightening and beneficial for future advancements.
In the design of the Urutau, we aimed to establish new standards for privately
manufacturable firearm designs or to uphold established, successful standards.
Guidance from George Dmitrieff's Submachinegun Designer’s Handbook significantly
influenced the design choices for the Urutau, and we recommend reading his book if
this section interests you.

Cartridge Choice
The Urutau, like many privately manufactured firearms, operates on a straight-
blowback mechanism. While this mechanism is relatively simple to implement, it
restricts our options for compatible cartridges. Fortunately, the Urutau is optimized for
the widely available and versatile 9x19mm Luger/Parabellum cartridge. Regarded as
the most common pistol and submachinegun cartridge worldwide, the 9x19mm Luger
cartridge offers an optimal combination of performance, availability, and compatibility
with blowback-operated firearms like the Urutau. This standardized cartridge offers
accessibility for builders across many developed and semi-developed countries and
maximizes the firearm's usability across various operational situations.

Barrel Length and Overall Length

Based on data from Ballistics by the Inch, the optimal barrel length for the 9x19mm
Luger cartridge is around 10 inches (254mm). The Urutau is designed with a default
barrel length of 250mm, providing adequate hand-clearance from the muzzle blast
while also most efficiently utilizing energy from the 9x19mm cartridge. In case the
user desires to comply with American firearm restrictions, the included ECM guide
accommodates 16-inch (407mm) barrels. Compared to a shorter 4.5-inch (114mm)
barrel, the Urutau's longer barrel length enables it to utilize approximately 22% more
energy from the cartridge. The bullpup configuration of the firearm contributes to its
compact overall length (OAL), allowing for a shorter firearm while maintaining a barrel
length that efficiently utilizes the energy of the 9x19mm Luger cartridge. This design
optimization balances both maneuverability and ballistic performance when compared
to other firearm designs.

Price
Improving upon the current state of the art presents a challenge. The cost to build an
FGC-9, including the printer, hardware, and materials for the first gun, amounts to
around $600, with subsequent builds totaling approximately $200 each. The Urutau
features a bolt designed to eliminate any welding requirements, eliminating the need
for welding hardware and reducing the initial price by roughly $100, depending upon
the builder's location. The estimated minimum cost to construct a Urutau stands at
around $500 for the initial gun, including printer and hardware, and $200 for each
subsequent gun.

Material Sourcing
One of the concerning weaknesses of the FGC-9 and Partisan 9 is that, although
minimally, they still rely on the acquisition of less-regulated gun parts for the build. For
example, they require AR-15 fire control group springs. Of Dmitrieff’s design
objectives, this was the biggest challenge we experienced when designing the
Urutau. The temptation to utilize parts which are difficult to standardize, privately
manufacture, or substitute was a constant distraction. However, our choices to utilize
easily accessible, less-firearm-related components improve supply chain resilience
and enhance the builder’s operational security when sourcing materials. The only
areas of significant vulnerability remain the thick-wall hydraulic pipe used to
manufacture the barrel and ammunition or ammunition components. Future
development in either of these areas is highly encouraged and appreciated.

Scalability
This is a non-issue for most Urutau builders, however with all necessary machines,
tools, and materials on hand and the time to treat the project like a full-time job, the
Urutau is manufacturable in less than a week. With extra printers, multiple competent
volunteers or employees, and a healthy supply chain, the Urutau’s manufacturing
process is easily scalable.

Bolt Core Bars

The FGC-9 posed a challenge to its builders when processing bolt core bars,
particularly due to the round bars being a challenge to weld in the correct orientation.
Additionally, cylindrical cores are less efficient in filling the space inside the upper
receiver. The Partisan 9 and Urutau address this issue, the Urutau by utilizing square
rectangular bars as the bolt core, being 20x12mm or ½”x¾” rectangular steel bar
stock. This standardized selection offers worldwide compatibility, accommodating both
imperial and metric standards and simplifying material sourcing for builders.

Weldless Construction
Unlike the FGC-9 and Partisan 9, which rely on welded bolt cores, the Urutau utilizes
a bolt that is pinned together and glued in place, significantly reducing both build
costs and the required skill of the builder. This innovation removes the necessity of a
welding machine from the construction process, making it simpler and more cost-
efficient.

Shortened Metal Firing Pin Channel

One of the most frustrating manufacturing steps to make an FGC-9 or Partisan 9 is
the process of drilling the firing pin channel out of a bar of metal. Though this is
possible with or without a drill press, it is still very tedious, and if the drill bit is canted
slightly or if the drill bit breaks, it could render the work useless. The Urutau
addresses this issue by significantly reducing the length of the steel bolt core piece
containing the firing pin channel. By predominantly housing the channel within printed
plastic, the metal drilling depth for the firing pin channel is reduced to 12mm or ½”.
Additionally, shortening the lower bolt core piece allowed for the cartridge pickup to be
made of solid metal, eliminating the necessity for welding or other workarounds to
construct a sturdy cartridge pickup.
Guide Rods
An additional enhancement we introduced in the Urutau is the implementation of two
steel guide rods. Inside the FGC-9, the bolt made direct contact with the upper
receiver, leading to wear on the bolt carrier housing and the internal walls of the upper
receiver. Although the Partisan 9 employs a single rod, an improvement over the
FGC-9, there remains the possibility for the bolt to contact the upper receiver walls.
On the other hand, the Urutau's bolt rides along two guide rods, minimizing contact
with the upper receiver’s walls. This design improvement not only reduces wear but
also eliminates the necessity for a buffer tube. This innovation enhances the durability
and longevity of the Urutau while simplifying its construction and maintenance
processes.

Telescoping Bolt
The Urutau features a telescoping bolt, a design commonly found in modern
blowback-operated firearms. With approximately 75% of the bolt mass positioned
over the barrel, this configuration increases bolt stroke and weight. As a result, felt
recoil is minimized, enhancing controllability during firing. This design improvement
enhances shooting comfort and accuracy, making the Urutau a more manageable
firearm to use.

Printed Fire Control Group

While 3D printed Fire Control Groups (FCGs) are not a new concept in 3D printed
firearms, the Urutau breaks new ground by introducing an FCG designed from the
ground up, drawing inspiration from the Steyr Aug FCG. This innovation compensates
for its plastic composition with small metal components, enhancing its durability to
withstand hundreds, or possibly thousands of rounds. By pushing the envelope in
FCG design, the Urutau establishes a new standard for reliability and longevity in
privately manufacturable firearms, ensuring consistent, reliable performance with
extended use.
Magazine
We chose the CZ Scorpion magazine for several reasons, primarily due to its long-
term reliability, ease of manufacturing, and user-friendly design. Despite its popularity,
and as a running joke, we did not consider Glock magazines, as Scorpion magazines
excel in these aspects. During testing, we experimented with printed STEN
magazines in an attempt to address feeding issues. However, after much
experimentation, we still found Scorpion magazines ideal. It is worth noting that
magazines with a double stack double feed configuration, such as the Scorpion's,
generally experience less internal stress. Double feed magazines are also
significantly easier to load in cold weather.

Usability
The Urutau is easy to use for any person of average physical capabilities. Aside from
the ejection port, the entire gun is ambidextrous. The controls are all extremely basic
so that non-English speakers with little firearm experience may intuitively understand
how to use them.

Safety Features
In addition to the manual safety mechanism, the Urutau incorporates safety features
to manage the risk of an out-of-battery detonation. The hammer's geometry is
designed to ensure that it cannot make contact with the firing pin unless the bolt is in
battery. In the unlikely event of an out-of-battery detonation, a specially engineered
channel redirects gasses upwards and away from the user, enhancing safety and
minimizing the risk of injury.

Form Factor
The form factor is inseparably linked to usability. The focus of the Urutau, aside from
recreational shooting, is urban combat and guerrilla warfare. With this in mind, we can
set some goals for the form factor: easy to conceal and use inside vehicles, easy
handling inside buildings and close-quarters environments, and an effective range of
25 to 100 meters.
The New Second Amendment
The New Second Amendment, a document we authored and included with the
Urutau, opens with the claim that the ideal privately manufacturable firearm has three
design objectives:
1. Practicality of Manufacturing Processes
2. Invulnerability to State Intervention
3. Competitiveness with Modern Standards
These three objectives often form a triple constraint, where most privately
manufacturable firearm designs pay little regard to one of the three. This is a trend
that the Urutau seeks to disrupt. Granted, these design objectives are idealistic;
achieving any one of them perfectly is impossible, and the degree to which an
objective is achieved is a matter of opinion.
We believe the Urutau makes significant advancements in all three design objectives,
however, it still has some notable issues. The manufacturing and assembly
processes, the ECM process especially, are challenging, and they have significant
pitfalls that may require the builder to start over. The thick-wall hydraulic tubing we
use to make the barrel and ammunition components remain vulnerable to state
intervention. As a pistol-caliber carbine, the Urutau is of little use beyond 100 meters
and struggles to pierce soft body armor.
These are a few examples of hurdles to overcome, but this is why we authored The
New Second Amendment. We cannot let innovation end here. We are only getting
started, and we would love for you to join us.

THE BEST HAS YET TO COME.

-RSmith28
-Zé Carioca