US 20120144985Al

(19) United States

(12) Patent Application Publication (10) Pub. No.: US 2012/0144985 A1
Beville et al. (43) Pub. Date: Jun. 14, 2012

(54) LIGHT WEIGHT MACHINE GUN (52) us. c1. ............................................................ .. 89/9

(75) Inventors: John Beville, BlytheWood, SC (57) ABSTRACT

(US); Greg Livermore, Columbia, A light-Weight machine gun is made by replacing selected
SC (US) components previously made of steel With interchangeable
components made of coated titanium alloy. Several different
(73) Assignee: FN Manufacturing LLC,
coatings are used on the components depending on the per
Columbia, SC (US)
formance requirements of the component as Well as factors
(21) Appl. No.: 12/050,979 related to convenience. The back sight bracket, the side
plates, bottom plate and cocking handle guide of the receiver,
(22) Filed: Mar. 19, 2008 and the carrying handle rod of the carrying handle assembly,
are made of titanium alloy coated With tungsten DLC; the
Related US. Application Data front block, also made of titanium alloy, is coated With a ?rst
coating of chrome nitride for resistance to Wear resistance and
(60) Provisional application No. 60/945,808, ?led on Jun. secondarily for high temperature resistance, folloWed by a
22, 2007. second coating of chrome carbo-nitride to provide the appro
priate appearance; and the titanium alloy carrying handle
Publication Classi?cation bracket of the carrying handle assembly is coated With boron
(51) Int. Cl. carbide. Performance of the lighter machine gun is equivalent
F41A 5/00 (2006.01) to the prior art carbon steel machine gun but With a Weight
F41F 1/00 (2006.01) reduction of over four pounds.
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US 2012/0144985 A1 Jun. 14, 2012

LIGHT WEIGHT MACHINE GUN [0006] The advantage of the replacement of the various
components With titanium alloy components is signi?cant
CROSS REFERENCE TO RELATED PATENTS Weight savings, helping to reduce the overall Weight by more
than four pounds. The advantage of the use of coatings is that
[0001] The priority bene?t of US. provisional patent appli performance of the coated surfaces of the M240E6 is
cation Ser. No. 60/945,808, ?led Jun. 22, 2007, is claimed. expected to be as good as the carbon steel surfaces of the
BACKGROUND OF THE INVENTION
components replaced and With no loss of interchangeability
With the prior art, carbon steel components of older M240Bs.
[0002] An important and basic part of the US Army small [0007] These and other features and their advantages Will
arms arsenal is the M240B machine gun. The M240B, ?rst be apparent to those skilled in the art of ?rearm manufacture
used by the US military in the late 1970s, is referred to as a from a careful reading of the Detailed Description of Pre
light-Weight machine gun. Compared to other machine guns, ferred Embodiments, accompanied by the folloWing draW
at about 27.5 pounds Without ammunition, it is one of the 1ngs.
heavier light machine guns. It is intended to be carried, along
With several belts of ammunition, by individual soldiers in BRIEF DESCRIPTION OF THE DRAWINGS
combat and to deliver sustained ?repoWer during an enemy
engagement. [0008] In the ?gures,
[0003] The M240B Would be less of a burden on the soldier [0009] FIG. 1 is a left side vieW of the present machine gun,
if it Were lighter. Accordingly, there remains a need for reduc according to a preferred embodiment of the present invention;
ing the Weight of the M240B. A likely route to reducing [0010] FIG. 2 is a right side vieW of the present machine
Weight, particularly if a redesign of the basic con?guration of gun, according to a preferred embodiment of the present
the M240B is to be avoided, is the substitution of lighter invention;
Weight metals, such as titanium alloys, Wherever possible for [0011] FIG. 3 is a right side, loWer perspective vieW of the
the heavier carbon steel currently used. Nonetheless, light machine gun of FIG. 2 With major components shoWn in
Weight metals, and titanium alloys in particular, do not have exploded relationship;
the same performance characteristics as carbon steel and are [0012] FIG. 4 is a left side, upper perspective vieW of the
not compatible With the remaining components particularly machine gun of FIG. 1 With major components shoWn in
in the environment of use of a combat machine gun. Accord exploded relationship;
ingly, While it may be helpful to consider, and even to try, [0013] FIG. 5 is a left side vieW of the receiver of the
titanium alloys for at least some of the components of the machine gun of FIG. 4 With its parts shoWn in exploded
M240B, the resulting performance may be altered for the relationship; and
Worse by such a substitution. Notwithstanding the advantage
[0014] FIG. 6 is a right side vieW of the receiver of the
in overall Weight reduction, performance suf?ciently machine gun of FIG. 3 With its parts shoWn in exploded
degraded may be unacceptable. Accordingly, there remains a
need for a Way to reduce Weight from the current M240B
relationship.
machine gun Without degrading performance.
DETAILED DESCRIPTION OF PREFERRED
SUMMARY OF THE INVENTION EMBODIMENTS

[0004] According to its major aspects and brie?y recited, [0015] The present invention is, in its most preferred
the present invention is an improved M240B machine gun. embodiment, a light-Weight machine gun based on the
The improvement is in the substitution of coated titanium M240B but With some of the components being replaced With
components for carbon steel components to reduce Weight. In coated titanium alloy components. The replacement compo
particular, the components of an M240B currently made of nents are dimensionally interchangeable With the carbon steel
carbon steel that are replaced in the present light-Weight components of the prior art M240B. The specially-coated
M240E6 With coated titanium alloy components are the titanium alloy parts are the receiver side plates, back sight
receiver side plates, bottom plate, cocking handle guide, back bracket, bottom plate, front block, parts of the carrying
sight bracket, front block, carrying handle rod and bracket. A handle, and cocking handle guide.
front sight collar is made of titanium in the improved machine [0016] Referring noW to FIGS. 1 and 2, there is shoWn a left
gun but not coated With the same special coatings as the other and right side vieW of machine gun 10, typical in appearance
titanium parts. In addition the ?nal exterior surfaces of the of the M240B machine gun used by the United States Mili
receiver of the present machine gun are coated With a ceramic tary. It has a buttstock 12, a receiver 14, a trigger assembly 16,
to eliminate shine and also to be able to apply a suitable a barrel 18, a heat shield 20, a front sight 22, a ?ash hider 24,
camou?age color. a carrying handle assembly 26, a rear sight 28, a feeder ramp
[0005] The coating for several, but not all, of these compo 30, and a bipod assembly 32. Carrying handle assembly 26
nents is tungsten diamond-like coating (DLC) applied to a includes a carrying handle bracket 34 and a carrying handle
thickness of 0005-0010 mm on Wear surfaces. For the front rod 36. For the most part, these components are dimension
block, tWo coatings are used, a ?rst coating of chrome nitride ally equivalent to the prior art components made of carbon
for achieving the requisite performance characteristics of steel and their function is the same.
Wear resistance and high temperature resistance, and a second [0017] FIGS. 3 and 4 shoW the same machine gun 10 With
coating of chrome carbo-nitride to hide the shiny surface of its major components shoWn in exploded relationship. In
the chrome nitride. For the carrying handle rod and cocking addition, top cover assembly 40 is shoWn separated from the
handle guide, a coating of tungsten DLC is used for Wear balance of receiver 14; and bipod assembly 32, including
resistance. Boron carbide is used to coat the carrying handle bipod bracket 42 and bracket bolts 44, and stock locking pin
bracket for high temperature resistance. 46 are also apparent.
US 2012/0144985 A1 Jun. 14, 2012

[0018] FIGS. 5 and 6 focus on receiver 14, and show its Wash, or preferably are blasted to achieve a surface that Will
parts from an upper left perspective, exploded relationship in bond Well With the coating to be applied. They are masked to
FIG. 5 and in upper right perspective, exploded relationship expose only those areas that need to be coated and then
in FIG. 6. Receiver 40 has back sight bracket 48, a left side subjected to the coating process.
plate 50, a right side plate 52, a bottom plate 54, a front block [0026] The coating for tungsten DLC is 0.001 to 0.005 mm
56, and gas cylinder 58. Steel rails 60, 62, are located on left
for most coated component surfaces, preferably at least 0.005
and right side plates 50, 52. Cocking handle guide 62 is mm for Wear surfaces but not more than 0.010 mm. The
carried by the outside of right side plate 52.
tungsten DLC measured static coe?icient of friction is 0.20 to
[0019] Those components of present machine gun 10 made
of titanium material must exhibit a loW coe?icient of friction,
0.26, and its measured dynamic coe?icient of friction is 0.20
loW Wear rate, good corrosion resistance, good compatibility to 0.24 although its coe?icient of friction in the literature is
With existing carbon steel components, and a dark, non-re 0.06 to 0.20. The exact coef?cient of friction is dependent on
?ective appearance. Front sight 22 and portions of the carry the surface to Which the tungsten DLC is applied. In general,
ing handle 26 are replaced With different material because, by the rougher the surface, the higher the coe?icient of friction.
doing so, machine gun 10 is lighter compared to the prior art It is deposited on a titanium material surface by physical
M240B. The performance requirements of these latter com vapor deposition (PVD), and by sputtering in particular.
ponents are not as critical as the subcomponents of receiver According to the literature, its maximum service temperature
40 made of titanium material. is 662° F. Its color is dark gray to black.
[0020] The choice of titanium material reduces Weight, and [0027] Boron carbide is not applied in as thick a layer as
the coating on the material alloWs the lighter-Weight material tungsten DLC; rather, it is applied to a thickness of 0.001 -0.
of machine gun 10 to perform in a manner comparable to that 005 mm. Its measured static coe?icient of friction is 0.19 to
of the carbon steel of the prior art M240B. Coating of the 0.33; its measured dynamic coe?icient of friction is 0.18 to
titanium parts prevents galling of the otherWise relatively soft 0.29. Boron carbide is also deposited by PVD, and by sputter
titanium surface. coating in particular. The literature identi?es its coef?cient of
[0021] The components that replace the prior art carbon friction as 0.12. Its maximum service temperature according
steel components are made of titanium material, preferably to the literature is 20000 F., and its color is also dark gray to
titanium alloy, and most preferably a particular alloy, Ti-6Al black.
4V, also knoWn as Grade C-5 according to ASTM B367 or
[0028] Front block 56, Which sees operating temperatures
titanium alloy according to AMS 4985, both of Which indus to 12000 F. is coated With a ?rst coating of chrome nitride for
try standards are incorporated herein in their entirety by ref Wear resistance and high temperature resistance, folloWed by
erence.
a second coat to front block 56 of chrome carbo-nitride to
[0022] The coating material for all but one of the titanium cover the shiny silver ?rst coating. The chrome nitride coat by
material replacement parts of receiver 14 (namely, front block itself is shiny silver in color and Would be unacceptable in a
56) is a diamond-like carbon (DLC), preferably tungsten military ?rearm as it shoWs up When night vision devices are
DLC. The part of receiver 14 having a coating other than used. Arc evaporation is used to apply these coatings.
tungsten DLC is front block 56, Which has tWo different
[0029] Chrome nitride is applied to front block 56 to
coatings, namely, a ?rst coating of chrome nitride folloWed by
achieve a coating thickness of 0.0005 to 0.005 mm; the
a second coating of chrome carbo-nitride. In addition,
chrome carbo-nitride is applied to a coating thickness of not
receiver 14 has a second coating, namely, a ceramic coating,
more than 0.006 mm, preferably 0.001 to 0.006 mm, and most
such as, for example, CERAKOTE applied by NIC Indus
preferably 0.002100002 mm by a PVD process
tries, to cover any shiny metallic areas and to alloW receiver
40 to take on a suitable color such as black or broWn or a [0030] The tungsten-DLC-coated titanium material
camou?age color. achieves speci?c performance requirements for use of those
[0023] Carrying handle assembly 26 includes carrying particular components in machine gun 10. Speci?cally, these
handle bracket 34 and carrying handle rod 36. The latter is components must be corrosion resistant, have high resistance
coated With tungsten DLC; the former With boron carbide to Wear, a loW coe?icient of friction, and dimensional and
because it comes into contact With the hot barrel and requires compositional stability at operating temperatures. For mo st of
good resistance to high temperatures. (Additionally, there are these components, the operating temperature is not likely to
steel and nylon components Within the carrying handle exceed 700 degrees F.
assembly that are not coated With tungsten DLC or boron [0031] Titanium material coated With DLC, and titanium
carbide.) Front sight 22 is also coated With phosphate along alloy coated With tungsten DLC in particular, meets the oper
With the rest of barrel 18. ating requirements surprisingly Well. Its performance on
[0024] Tungsten DLC is an amorphous coating With tetra receiver side plates 18 With respect to Wear appears to be
hedral bonding, and is available from manufacturers such as better than chrome electrolytically deposited on steel.
lonBond of Greensboro, NC. Tungsten DLC is applied by
physical vapor deposition (PVD), and by the technique Example 1
knoWn as sputtering in particular, Which process is Well
knoWn. The duration of the process determines the thickness [0032] A light-Weight machine gun made according to the
of the coating. A thicker coating requires continuation of the present machine gun 10 design Was tested by ?ring 20,000
process longer than a thinner coating. rounds of ammunition With it. The test Weapon broke in (that
[0025] Proper surface preparation of the titanium material is, increased and then leveled off its operating group velocity)
is critical. Prior to coating, all titanium alloy parts are thor prior to 2000 rounds, typical of M240B machine guns. There
oughly cleaned to remove, dirt, dust, grease, oil and other Was no evidence of Wear of the tungsten DLC-coated com
foreign substances. The surfaces are then given a chemical ponents even after 20,000 rounds. The rate of ?ring and
US 2012/0144985 A1 Jun. 14, 2012

operating group velocity Were measured to be Within normal Wherein said back sight bracket, tWo opposing side plates,
speci?cation limits and the average measured rate of ?re Was cocking handle guide and bottom plate are made of
580 rounds per minute. titanium material having a coating of a Wear-resistant
Example 2 material.
2. The machine gun as recited in claim 1, Wherein said
[0033] A light-Weight machine gun made according to the
present machine gun 10 design Was tested by changing barrel Wear-resistant material is a diamond-like carbon (DLC) coat
18 1000 times to test the Wear on front block 56, counting the ing.
number of clicks needed to install barrel 18 and comparing 3. The machine gun as recited in claim 2, Wherein said DLC
that to the results of a prior art M240B. Performance of the is tungsten DLC.
coated front block 56 equaled that of the M240B. 4. The machine gun as recited in claim 3, Wherein said
[0034] The use of coated titanium alloy substitute compo coating is betWeen 0.005 and 0.010 mm thick.
nents and sub-components signi?cantly reduces the Weight of 5. The machine gun as recited in claim 1, Wherein said
M240E6 beloW that of M240B by approximately four pounds titanium material is a titanium alloy.
Without compromising on performance characteristics and 6. The machine gun as recited in claim 5, Wherein said
full interchangeability. The performance of tungsten DLC titanium alloy is Ti-6Al-4V.
exceeded that of nickel boride, Well-knoWn as a titanium 7. The machine gun as recited in claim 2, Wherein said front
coating material but Which tended to chip and to exhibit poor block is coated With a ?rst coating of chrome nitride.
dimensional stability. 8. The machine gun as recited in claim 7, Wherein said ?rst
[0035] It Will be apparent to those skilled in the art of the coating is 0.0005-0.005 mm thick.
manufacturing of moving metal components that the present 9. The machine gun as recited in claim 7, Wherein said front
invention, de?ned by the appended claims, can be applied to block is coated With a second coating of chrome carbo-ni
other components besides light Weight machine guns, as tride.
described in the preferred embodiment, Without departing 10. The machine gun as recited in claim 9, Wherein said
from the spirit and scope of the present invention, as herein second coating is not more than 0.006 mm thick.
after claimed. 11. The machine gun as recited in claim 10, Wherein said
What is claimed is: second coating ranges from 0.001 to 0.006 mm thick.
1. A machine gun, comprising:
12. The machine gun as recited in claim 1, Wherein said
a stock; receiver body has a ceramic coating.
a receiver body attached to said stock, said receiver body
including a back sight bracket, tWo opposing side plates, 13. The machine gun as recited in claim 1, Wherein said
a bottom plate, a cocking handle guide, a ?re control carrying handle bracket is made of titanium material With a
spring, and a front block; heat-resistant coating.
a receiver cover attached to said receiver body; 14. The machine gun as recited in claim 13, Wherein said
a feeder ramp carried by said receiver body; heat-resistant coating is boron carbide.
a trigger assembly in operative connection With said 15. The machine gun as recited in claim 1, Wherein said
receiver, said receiver carrying said trigger assembly; carrying handle is made of titanium material having a coating.
and 16. The machine gun as recited in claim 1, Wherein said
a barrel in operative connection With said receiver body, coating is tungsten DLC.
With 17. The machine gun as recited in claim 1, Wherein said
a heat shield, front sight collar is made of a titanium material.
a carrying handle, 18. The machine gun as recited in claim 17, Wherein said
a carrying handle bracket, titanium material is coated With phosphate.
a front sight collar, and
* * * * *
a bipod;