Discrete Spacegun - 9
9mm Compact AR-Style pistol.
Required materials:
Gun parts:
-9mm AR-15 bolt
-AR-15 charging handle
-9mm AR-15 barrel
-AR-15 buffer
-AR-15 buffer spring
-AR-15 trigger
-AR-15 magazine catch spring
Screws:
Flat countersunk Phillips screws size 8-32 machine screws
7x 8-32, 1 5/8 in (To attach barrel retainer to upper, also front take down)
1x 8-32 ⅞ in (Rear take down)
Hex Socket Button Head Cap Screws Bolts, varying sizes depending on your configuration.
https://www.amazon.com/iExcell-Stainless-Socket-Button-Washers/dp/B07L65DHV6
Quantity x Length
6 x 12mm (To connect top and bottom barrel shroud.)
1 x 8mm (To secure bottom of barrel shroud to lower.)
2 x 20mm (To attach ejector.)
1 x 12mm (Grind down the button head’s sides to make a grub screw and secure the buffer
into the buffer tube.)
1 inch wide Kapton tape
Print orientation:
Use the above picture for optimal orientation. Some have had success printing the combined lower
receiver and buffer tube at 45 degrees on smaller print beds. To avoid this, you may choose one of the
split lower/buffer tube options. Please note that all part files are already set to the correct orientation,
above picture is for reference only if needed.
Print settings:
Layer height: 0.15mm
Walls 8 lines
Infill 98-100%
Temperature 210C
Please ensure your flow and line width settings are set correct such that your walls touch.
Material tested with: Esun PLA Plus
Many Polymaker PLA Plus are known to be quite strong.
Venturing outside of these recommendations may give you untested results.
Lower receiver, upside down.
Upper upside down.
Lower hand guard, upside down
Upper hand guard (barrel retainer) on end, front side up.
Grip, flat side down, right side up.
Magazine catch: on side as depicted.
Assembly:
Installing the buffer:
Install the AR buffer and buffer spring, using a retaining screw to hold them in place. You may
use the charging handle to hold the buffer back while you install the retaining screw. (left)
Note on retaining screw, I used a 15mm screw and ground
down the sides of the head until it fit in the groove in the
bolt. (right)
You may find other methods of installing the
retaining screw preferable. (right center)
To heat set, you may use a soldering iron to heat
up the screw as you install it.
Use your driver to hold the screw to the desired
hole, twist as far as it will without undue
resistance.
Apply heat to the side or head of the screw, once
it heats enough, the plastic on the sides of the
hole will soften and deform allowing you to
continue to turn the screw, forming threads as you turn.
Remove the heat source and allow the newly formed
threads to cool.
Installing the retaining screw through the top should
look like this. (bottom right)
Install the Fire Control Group:
A printed fire control group will work, but I would recommend the Anderson trigger found here:
https://andersonmanufacturing.com/hammer-trigger-kit-stainless.html
Some have experienced issues with the standard hook shaped hammer in AR-9s (credit to P-80 Ralph.)
For a little nicer trigger pull, I would also recommend ordering a reduced power trigger spring kit.
Otherwise, install the fire control group following the normal procedure for an AR style lower.
Link if needed:
https://www.youtube.com/watch?v=blDByRL9-co
Install the Ejector:
Insert the Ejector fin into the slot for it behind the top of the magazine well.
Insert the 2 screws into the side to secure the fin into place.
You may need to heat set the screws as you install them.
Install the Grip:
Heat set the threads for your grip screw first, then let cool and remove the screw.
Remember to install the fire select detent and detent sprint as you install your chosen grip.
If you over-tighten and damage the heat set threads, you can repair them by taking out the screw,
melting a little additional plastic into the grip screw hole, and re-forming your threads.
You may want to print and try out several grips to find what best suits you and your purpose.
Install the Magazine Catch:
The magazine catch will go into the right side of the lower and a hole will line up. Use a M3 screw
inserted through top to secure the catch and spring. You may need to heat set the screw.
Attach the lower hand guard to the lower receiver.
You may need to clean up the print some for a tight fit, using a heat gun to soften the plastic can also
help. Use the at the front of the lower hole for a retention screw at the base of the lower hand guard.
Slide your chosen hand guard onto the receiving rails forward on the lower receiver. Clean and adjust
your parts until they fit and the holes for the retaining screw line up on the underside. Install your
retaining screw, heat setting the screw may provide a better connection.
Installing the barrel and upper hand guard:
Fitting the barrel:
You may need to do some sanding and scraping with a hard edge to fit the barrel to the upper
receiver and hand guard.
If your barrel does not tightly fit into your upper receiver and retainer, use 1 inch wide Kapton tape
one layer at a time until the fit is tight. This may also help reduce heat transfer.
Assembling the upper:
Use a long Phillips screw driver to install the 6 retainer screws. You may need to heat set
the threads into the upper receiver first.
Insert the charging handle and bolt into the upper receiver.
Assembling the Upper and Lower Receivers:
Secure the upper and lower receivers with the front and back screws.
Secure the upper and lower hand guards to each other with the bolts and M3 screws.
Screws and nuts should align between the upper and lower hand guard, if they do not match perfectly,
they can be cleaned up with a drill bit by heat setting the screw depending on how much variance you
have.
Optional Velcro strap may be used to secure magazine to gun for storage.
Alternate Buffer Tube Options
Alternate buffer tube options are available Assemble as shown above.
2 piece printed lower (right) is secured together by 4 8-32 3 inch screws.
Standard Buffer tube (center) is secured by a hose clamp.
Additional Accessories
In the folder Misc, there is a light mount. This is designed for this style of handheld light.
https://www.amazon.com/gp/product/B016ZPH470
Any M-lock style accessories can be attached with a M4 screw and a M4 T-nut.
https://www.amazon.com/gp/product/B0894T22YR
Parts recommendations:
Your build may vary.
https://andersonmanufacturing.com/hammer-trigger-kit-stainless.html
https://davidsondefense.com/eld-performance-45-oal-9mm-medium-profile-110t-4150-crmov-nitr
ide-12x36.html
https://davidsondefense.com/Custom-Deal-BCG-Charging-Handle-Combos-AR-15-M4-Milspec-
Charging-Handle-United-Defense-Labs-9mm-Bolt-Carrier-Group_p_8843.html
(any 9mm bolt you can find on sale should do.)
https://davidsondefense.com/ar-15-m4-government-carbine-recoil-buffer-3-oz
https://davidsondefense.com/standard-ar-15-carbine-recoil-spring
https://davidsondefense.com/davidson-defense-ar-15-standard-mil-spec-right-hand-safety-selec
tor
https://www.dollartree.com/plastic-dart-shooter-playsets/263063 (optional source for magazine
catch springs)
You may want to replace the trigger spring with some or reduced power, it can be a very cheap
trigger upgrade.
Special Thanks:
Geometry borrowed:
Firebolt
FGC-9
Biden’s Bane
The ARK
Beta testers:
nikolai.romanov
Tedyhere
P-80 Ralph
