browning machine gun cal .30 - technical air intelligence report 21 - examination of japanese...

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T E C H N I C A LAIR INTELLIGENCE

CENTER

# 2 1EPORTEXAMINATION OF JAPANESE

"BROWNING" MACHINE GUN

l?JTm»GENCE LIBRABY1 0 '-"•'• - i U . t ,

Issued by the D.vision 0 f Naval Intelligence

By

C ombi ne d , Personnel * of United States an d British Services

for the Use of All.ed Forces

TECHNICAL AIR INTELLIGENCE CENTER

NAVAL AIR STATION ANAC OSTIA D C



EXAMINATION OF JAPANESE "BROWNING" MACHINE GUN

FOREWORD

A J a p a n e s e a i r c r a f t " B ro w n in g " . 5 0 c a l i b e r m a c h i n e gun (BMI # 4 3 7 - CEE # 2 9 5 0 ) S e r i a l # 2 3 4 9 ,m a n u f a c t u r e d i n November 1 9 4 2 , w as r e c e i v e d f r o m t h e T e c h n i c a l A i r I n t e l l i g e n c e C e n t e r , N a v a lA i r S ta t i o n , A n a c o s t i a , D . C . fo r m eta l l u rg i ca l ex a m i na t i o n . The g un w as ca ptured a t I a e , NewGu ine a, on Septem ber 1 6 , 194 3, comple te and in good working ord er . I t had been used for anom inal per io d of t im e on a Japane se fi g h te r CSCAR.

Markings found on the gun are rec ord ed i n Figu re 3 of the Appendix. The weapon weighed5 1 - 1 / 2 p o u n d s w h e n r e c e i v e d .

Seventeen per cent of the metal parts used in the manufacture of the Japanese "Browning" .50c al ib er machine gun were made from tun gst en s t e e l , thr ee per cent from nickel -chromium s t e e l , andth e remainder were un al loy ed . The s t e e l s were made in the bas ic open hearth or e le c t r ic furnacewith graded scrap forming a large part o f the charge.

The weapon was cop ied from an ea rl y American model wi th minor m od i f i ca t io ns . Heat tr e a t-Bent s w ere s i mpl er tha n A mer ica n pr a c t i ce s , a nd f la me ha rden i ng w as us ed ex t en s i v e l y . An i n te r e s t i n g f ea tur e w as chro mium p l a t i n g i n the bo re of the b a r re l .

ECONOMIC COIBIDERATIONS

The gun shows manufacturing methods s imilar to other Japanese guns examined and displayedgood workmanship. Bea ring parts pos ses sed a good f i n i s h whi le a large number of ex te ri or s ur fa ce s showed hand f i n i s h in g . No brazed or s tamped par ts were used .

Contrary t o American and German p r a c t i ce s , bu t in keep ing wi th the ir own, the Japanese usedhig h-c arb on tu ng ste n s t e e l (carbon .59% - .67%, tun gste n 1.7% - 2 .2%) in part s subje cted t oextreme wear . Re s id ua l amounts of o the r a l lo y i ng e lements ind ic at e the use of graded scrap int h e f u r n a c e c h a r g e s .

The ex te ns i v e us e o f f la me ha rden ing on the pa r t s i s a n i nd i ca t i o n o f co ns erv a t i o n o f he a t -t r e a t i n g e q u i p m e n t .

DISCUSSION OF RESUITS

The Japanese "Browning" machine gun as -r ec eiv ed and disasse mb led i s shown in Figu res 1 t o 3 ,i n c l u s i v e , i n the A ppendi x . W hi le th i s g un w as o bv i o us l y co p i ed from a n ea r l y A mer ican des i g n ,so me f e a t u r e s a r e o f i n t e r e s t an d a r e d i s c u s s e d i n d e t a i l .

The bore of th e ba rr el of t h i s gun was chromium pl at ed from the sh ou lde r of the chamber t ot h e m u z z l e . V er y l i t t l e wear had occu rred at eac h end where the p la ti ng showed a th ic kn es s of.000 080 in ch . The p la t i ng was a lmost en t i r e ly removed from the should er up to about 6 inche sback of th e mu zzle . The chromium pl at in g seemed to have a sa t i s f ac to ry ad her enc e, as the re wasno ev i de nce o f f l a k i ng o f f . Th i s ba r re l had a ppa ren t l y had co ns i d era b l e s e rv i c e .

T y p e o f S t e e l

Ea ch pa r t w as s pa rk t e s t ed a nd ca re fu l l y i ns pe c te d . Tho se sho w ing unus ua l f ea tu res w e^e

ana lyze d and the r e s u l t s shown in Tables 1 and 2 in the Appendix .

Tw enty pa r t s w ere fo und to co nta i n tung s t en i n l i b er a l a mo unts. The us e of tung s ten s t e e l sin machine guns appears to be s tandard Japanese pract ice as ev idenced in previous reports submi t t ed o n th i s p ro je c t . The cho i ce o f th i s a l l o y a ppea rs to be o n the ba s i s tha t the s e pa r t s a resu bj ec te d to extreme we ar. However, as ev idence d by the ph ys ic a l t e s t s made on the gun ba rr el(Ta bl e 3 ) , i t i s d o ubt f u l tha t the w ea r re s i s ta nc e o f tun g s ten s t e e l s w ould be i mpro ved ov erth a t o f a p l a i n carbo n s t e e l o f equa l ha rd nes s . The ca rbo n a nd tung s ten l e v e l s us ed a re not h i g he n ou g h t o / p r o d u c e w e a r - r e s i s t a n t , f r e e t u n g s t e n c a r b i d e p a r t i c l e s , an d t h e p a r t s a re n ot m a ss iv ee n ou g h t o r e q u i r e a n y a l l o y i n g e le m e n t f o r h a r d e n a b i l i t y .

- 1



The steels appear to have been made In the basic open hearth or electric furna ce. They were•ilicon and aluminum kille d. The residu al amounts of various alloying elements indicate the useof considerable scrap in the char ges. Aluminu m may have been added in some cases for grain sizecontrol.

A minor number of small parts were made from high-sulphur screw stock for its free machining qualities.

Heat Treatment

Seven ty-tw o per cent of the 115 parts examined were heat treated. Thi s is a high percent age for Japanese practice , but the treatments appear simpler than America n specificatio ns sinceonly the firing pin and the extractor were differentially har dened. The bol t, for example, wasuniform ly heat treated to a lower hardne se than specified on the American counter part. Hardeningof wearing parts was accomplished by flame heating and quenching.

Method of Manufacture

Of a total of 115 parts available for examination, the following distribution according tomanufacturing method was made:

22% - Forged and machined1+2$ - Machined from bar stock11$ - Coiled wire springs

U& - Cut from rod or wire11$ - Cut from plate or sheet

These ratios are in proportion to other Japanese machine guns exam ined . Howev er, the advantage of forging was largely lost through improper forging and machining.

Careful examination of the barrel revealed that it had been rifled rather than broached*

Exterior Coatings

All the outer parts of the gun were given an oxide chemical treatment by dipping to producea dark dull finish. This treatment, while producing some corrosion resist ance, is designed principally to reduce reflectivity.

The automatic trig ger housing (#97) was nickel plated .00006" on the entire exterior surface;

the auxiliary hand-cocking lever extension (#112) was cadmium plated .0002"j and the breech lockdepressors (#17) were chromium plated e00005

nover the flame hardened wearing surface.

-2



27723

Figure 1. Japanese "Browning" 12.7 mm.(.50 cal.) machine gun as-received. (BMI #437) - Figure 2. Japanese "Browning" 12.7 mm.

machine gun disassembledo(CEE #2950)

-3

30821



27722

Figure 3 . Clos e-up view of .housing assembly attachments

-A



31309

Figure L. Macroetched view of the accelerator showingflow lines and flame-hardened area.

ISw

^̂W w w& ^ > • 'i

Figaro 5. Micrograph of ty pi ca l tungstens t e e l c o r e ,

N it al Etch 1000XVick ers Hardness 280

iLi

1

-5



TABLE 1. DETAILS OF MANUFACTURE OF JAPANESE "BROWNING" .50 CALIBER

MACHINE GUN (BMI #437 - CEE # 2950)

Part Weight, Hardness, Microstructure and

No. Name Grams Vickers Remarks Heat Treatment

1 Housing Assembly 8,825 248 Three forgings and two Quenched and highly

plates of SAE 1080 steel tempered.

riveted together. Rivets

of low carbon steel.

2 Housing Cover 736 268 Forged from SAE 1080 steel. Quenched and tempered.

Not differentially

hardened.

3 Housing Cover -atch 27 312 Forged from medium carbon Quenched slightly below

steel. the critical range

and tempered.

4 Housing Cover Latch 53 258 Tw o pieces machined from Quenched and•tempered.

Guide bar stock and fusion Heat treated after

welded together. welding.

5 Housing Cover Latch 7 Stamped from high carbon

Spring steel sheet.

6 Housing Cover Latch 4 536 Cut from medium carbon Quenched and tempered,

Pin steel rod.

7 Housing Cover Guide 127 core 255 Forged from medium carbon Quenched and tempered.case 613 steel. Flame hardened Flame heated and

case .05" on wearing quenched.

surface.

8 Barrel 2,975 295 Forged from tungsten sbeeL Quenched and tempered.

Rifled bore.

9 Barrel Extension 1,320 core 258 Forged from tungsten steeL Quenched and tempered.

case 689 Flame hardened in groove Shows small MnS in-

corners only. clusions. Flame

hardened.

10 Barrel Jacket 909 220 Machined from SAE 1040 Annealed. Excess MnS

steel bar stock or inclusions.

tubing.

11 Barrel Jacket 291 351 Machined from medium car- Quenched and tempered.

Extension bon steel bar stock or

tubing.12 Barrel Booster 95 273 Machined from tungsten Quenched and tempered.

steel bar stock.

13 Barrel Booster H4 267 Machined from medium car- Quenched and tempered.

Retainer bon steel bar stock.

13A Barrel Booster 8 580 Machined from medium car* Quenched and slightly

Retainer Lock bon steel sheet. tempered.

U Breech Lock 151 core 480 Machined from tungsten Quenched and tempered

case 733 steel bar stock. Flame core. Flame heated

hardened on top wearing .O65wand quenched.

surface.

15 Breech Lock Cam 284 292 Forged from low tungsten Quenched and tempered.

steel*

16 Breech Lock Cam Bolt 38 187 Machined from mild carbon Normalized.

steel bar stock.

17 Breech Lock 22 core 505 Machined from medium car- Core quenched slightly

Depressors case 795 bon steel bar stock. below critical range

Flame hardened on wear- and tempered. Shows

ing surface and chrome undlssolved carbides.

plated .00005w. Case flame heated .08"

and quenched.

18 Breech Lock 1 Machined from low carbon Normalized. Shows MnS195Depressor Pin steel bar stock. inclusions.

18A Breech Lock Pin 15 483 Machined from tungsten Quenched and tempered.

steel bar stock.

18B Breech Lock Spring High carbon steel strip.

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TAB LE 1. (CQWT.1)

Part Weight, Hardness, Microstructure andNo. Name Grams Vickers Remarks Heat Treatment

19 Belt Feed Cover 84 345 Forged from medium carbon steel bar stock.

Quenched below criticalrange and tempered.Shows undissolved car

20 Belt Feed Pawl 360 Machined from medium carbides .

Quenched below critical

35bon steel bar stock. range and tempered.

Shows undissolved carbides.

21 Belt Feed Pawl 458 Forged from medium carbonsteel. Riveted to pawl.

Quenched and tempered.Shows undissolvedcarbides.

22 B elt Feed Pawl Pins 3 218 Cut from medium carbon Hot rolled and normalizsteel rod. ed.

23

24

Belt Feed PawlSpring

Belt Feed Lever

1

152 337

High carbon steel coiledwire spring.

Forged from medium carbon

Cold drawn.

Quenched below criticalsteel bar stock. Flamehardened on tips. Not

range and tempered.Shows MnS inclusions

differentially hardened. and undissolved carbides. Flame heated.36" and quenched.

25 Be lt Feed Lever Bo lt 27 295 Machined from medium car- Normalized.bon steel bar stock.

26 B el t Feed Lever Washer 2 200 Cut from low carbon steel Rolled and normalized.sheet.

27 Cartridge Feed Retainer 22 core 383

case 713

Machined from medium carbon steel bar stock.Flame hardened on wear-

Core quenched and tempered. Case flameheated .08" and tem

23

29

30

Cartridge FeedHinge Pin

Cartridge Feed RetainerSpring

Cartridge Receiver Stop

7

62

174

270

ing surface.Machined from medium car

bon steel bar stock.High carbon steel coiled

wire spring.Machined from medium car

bon steel bar stock.

pered.Spheroidized condition.

Cold drawn.

Quenched and highly tempered. Shows undissolved carbides.

31 Cartridge Receiver Pin 3 Low carbon steel. Hot rolled and normalized stee l. Hot headed and annealed.

32 Bo lt 1,556 303 Machined from tungstensteel bar stock.

Quenched and tempered.

33 Bolt Decelerator 64 coreease

265713

Machined from tungstensteel bar stock . Flame

Quenched and tempered.Case heated by flame

hardened on wearing and quenched.

surface.

34 Bolt DeceleratorHinge

19 pinar m

258168

Pin machined from mediumcarbon steel bar stock.Arm cut from high carbon

Pin rolled and normalized. Arm spheroidized.

steel strip. Pin mach

ined down at head andused as rivet to attacharm.

35

36

37

Bolt DeceleratorSpring

Bolt DeceleratorSpring Cap

Bolt Decelerator

1

5

37

319

415

High carbon steel coiledwire spring.

Machined from medium carbon steel bar stock.

Cut from drawn wire.

Cold drawn.


Cold drawn.

Spring Cap Locking

38Pin

Bo lt Rele ase Lever 40405 Forged from medium car

bon steel.


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TABIE 1. (CONT.)

Part Weight, Hardness, Microstructure andName Grams Vickers Remarks Heat TreatmentNo.

39 Bolt Release Lever 16 490 Machined from tungsten Quenched and tempered.Pin steel bar stock.

40 Accelerator 16 8 corecase

360628

Forged from tungstensteel. Flame hardenedon wearing surface (seeFigure 4) .

Core quenched slightlybelow critical rangeand tempered. Caseflame heated .08" andquenched.

Accelerator Pin 27 423 Cut from medium carbonsteel rod.

Quenched and tempered.Shows small amountsof undissolved carbides .

42 Accelerator Catch 93 corecase

28 0

700

Forged from tungsten steel.Flame hardened on workingsurface.

Quenched and highlytempered. Shows t i t a -nium n it ri de and MnSinclusions. Flamehardened .25" andquenched.

43 Accelerator CatohLock Pin

3 245 Cut from mild carbonsteel rod.

Rolled and rapidlycooled.

44 Accelerator Lock 19 51 0 Cut from high carbon Quenched and tempered.

45

46

SpringFiring Pin

Firing Pin Spring

13

11

backpoint

575883

steel sheet.Forged from tungsten

steel bar stock.High carbon steel coiled

Differentially quenchedand uniformly tempered.

Cold drawn.

47 Firing Pin SpringContainer

55 388wire spring.

Machined from tungstensteel bar st ock.

Quenched and tempered.Shows MnS inc lu si o n s.

48 Firing Pin Spring •Stop Pin

379 Cut from medium carbonsteel rod. End ma-

Quenched and tempered.Shows excess carbides.

8 chined down and used asrivet to attach arm.

49 Firing Pin Spring •Stop Arm

419 Cut from medium carbonsteel sheet.

Quenched and tempered.Shows excess carbidesand titanium nitrideinc lus ions .

50 Sear 18 395 Forged from Ni-Cr-fl steel Quenched and tempered.but not differentiallyhardened.

51 Sear Spring 1 - High carbon steel coiled Cold drawn.

52 Sear Slide 5 395wire spring.

Machined from low Ni-Crsteel bar sto ck.


53

54

Cocking LeverDriving Spring Rod

17

99404

186Forged from tungsten steel.Machined from mild carbon

Quenched and tempered.Hot rolled and normal-

stee l. Head and rod one ized.

55 Outer Driving Spring 81 608piece.

High carbon steel coiled Cold drawn.

56 Inner Driving Spring 33 -

wire spring.

High carbon steel coiled Cold drawn.

57 Extractor 82 core

case

280-379

,432

wire spring.Forged from tungsten steel*

Flame hardened and differentially heat treated,

Differentially quenchedand uniformly tempered.Flame heated .055" and

58

59

Extractor Depressor

Extractor Cam Guide

16

35 corecase

608

312

509

Stamped from high carbonsteel sheet.

Forged from medium carbons t e e l .

quenched.Quenched and slightly

tempered.Quenched and tempered.

Flame hardened .04°on edges and quenched.

-8



TABIE 1. (CONT.)

Part Weig ht, Hardness , Micro8tructure andHo. Name Grains Vic ker s Remarks Heat Treatment

60 Extractor Cam Guide 5 153 Machined from loir carbon Normalized.Nut steel bar stock.

61 Extractor Cam Guide 1 570 High carbon steel wire Cold drawn.Spring clip.

62 Ejector 9 293 Forged from medium carbon Quenched and tempered.steel bar stock.63 Ejector Spring - - High carbon steel coiled Cold drawn.

64 Ejector Pin 1 261wire spring.

Cut from medium carbon Quenched and highly

65 Recoil Housing 795 284steel rod.

Forged from tungstentempered•

Quenched slightly belowsteel.•Oil".

Carburized case the critical range andtempered. Case isquenched and temperedshowing undis8olvedcarbidos.

66 Main Recoil Spring 127 362 SAE 1070 Modified steelcoiled wire sp ring.

Cold drawn. Decarburised surface.

67 Secondary Recoil

. Spring

46 326 SAE 1080 steel coiled wire

spring.

Cold drawn.

68 Spring Buffer Tube U6 266 Machined from medium carbon steel bar stock.

Quenched and highlytempered. Shows undissolved c arbides.

69 Spr ing Buffer Tube Rod 45 435 Machined from medium carbon steel bar stock.

Quenched and tempered.Shows MnS inclusionsand undi3solved carbides•

70 Sp ring Buffer TubeGuide

33 220 Hot headed from mediumcarbon ste el.

Annealed after headingoperation.

71 Sp rin g Buffer Tube Cap 16 179 Machined from mild carbon steel screw stock.

Normalised.

72 Sp rin g Buffe r Tube Head 29 302 Machined from low tungsten steel bar stock.


Shows excess carbides.

73

74

75

Spring Buffer TubeInner Spring

Spring Buffer TubeOuter Spring

Spring Buffer Tube Seat

8

29

62

-

562

400

High carbon steel coiled

wire spring.High carbon steel coiled

wire spring.Machined from tungsten

steel bar stock.

Cold drawn.

Cold drawn and tempered,Decarburized .004"•

Quenched and tempered.Shows large amountsof MnS inclusions.

76 Spring Buffer TubeCover

72 core 300case 700

Machined from SAE 1070modified steel barstock. Face,flame

Quenched and tempered.Base flame heatedand quenched.

hardened.

77 Spring Buffer Tube Pin 4 284 Cut from medium carbonsteel rod.

Quenched and tempered.Shows signs of decarbur zat ion.

78

79

Auxiliary Buffer Spring

Back Plate

65

850

500

300

SAE 1080 steel coiled

wire spring.Forged from SAE 1080carbon steel.

Quenched and tempered.Decarburlzed .003"•

Quenched and highlytempered. Shows excesscarbides•

80 Back Plate Cap 99 144 Machined from medium carbon steel bar stock.

Highly annealed.

81 Back Plate Bolt 111 240150

DittoMachined from mild carbon

Annealed,Normalised,

82 Back Plate Bolt Nut 5 steel bar s tock.

83 Back Plate Latch Pin 17 374 Machined from medium carbon steel bar stock.


-9



TABLE 1. (CONT.)

Part We ight, Hardnes s, Microstructure andNo. Name Grams Vickers Remarks Heat Treatment

84 Back Plate Lock Bolt 61 260 Machined from AESI Normalized.A513O steel bar stock.

85 Pin Cocking Lever 11 440 Forged from medium car- Quenched and tempered.bon steel.

86 Trigger Bar Extension 64 corecase

385689

Machined from tungstensteel. Quenched and tempered.Carburized case .04"

on ends .87 Trigger Bar Extension

Pin17 pin

arm400175

Pin cut from medium carbon steel bar stock.Arm cut from high car-

Pin quenched and temp-er ed . Arm sph ero i-d i zed .

bon steel strip. Pinmachined down at headand used as rivet toattach arm.

88 Mechanical Trigger 23 660 Forged from medium carbon steel*

Quenched and sligb lytempered.

89 Mechanica l Trigger High carbon steel coiled

90Spring

Mechanical TriggerGuide

33 weldmetal

134190

wire spring.Welded bar stock and

curved metal of medium

Not heat t re ate d aft erwelding. Normalized.

carbon steel .

91 Mechanical TriggerScrews

1 292 Machined from mild carbon steel.

Quenched and highlytempered.

9293

94

Mechanical Trigger NutAutomatic Trigger

Automatic TriggerRetainer

36

10

corecase

corecase

-365700

376680

Cut from mild carbon steel.Machined from Ni-Cr steel

bar stock.

Machined from Ni-Cr steelbar stock.

Quenched and tempered.Carburized .04" deepon t i p

Quenched and tempered.Carburized on wearing

95 Automatic Trigger •30 core 374 Dittosurface .04" deep .

D i t t oPiston case 708

96 Automatic Trigger 0f 536 High carbon steel coiled

wire spring.

Cold drawn wire.

Spring Machined from low carbon Annealed.7 Automatic Trigger 255 124Housing steel bar stock. Nickel

98

99

100

101

102

103

104

105

106

Automatic Trigger

Butterfly NutAutomatic Trigger

Pressure By-pass

Automatic TriggerHousing Bolts

Automatic TriggerHousing AttachmentBolts

Automatic TriggerHousing AttachmentNuts

Automatic TriggerHousing AttachmentWashers

Hand Cocking Lever

Hand Cocking Lever

StudHand Cocking Lever Pin

25

25

3

16

11

4

410

18

11

160

steel 164copper 133

205

-

218

216

200

350

410

plated on exterior.00006".

Machined from medium carbon steel bar stock.

Machined from medium carbon steel bar stock andcopper bushed.

Headed from mild carbonsteel.

Headed from mild carbonsteel.

Cut from mild carbonsteel bar stock.

Cut- from mild carbonsteel bar stock.

Hook bent from mediumcarbon stee l.

Machined from mediumcarbon steel bar stock.

Cut from medium carbons t e e l r o d .

Rolled and annealed.

Stee l normal ized .Copper cast.

Hot headed and annealed.

Hot headed and annealed*

Normalized.

Normalized.

Normalized.

Quenched below cri t icalrange and tempered.

Quenched below cri t icalrange and tempered.

- 1 0



TABLE 1.

Part Weight, Hardness, Microstructure andN o. Name Grams Vicker s Remarks Heat Treatment107 Hand Cocking Lever 29 20 0 Machined from mild car- Normalized.

Front Guide Bracket bon st e e l pl at e.10 8 Hand Cocking Lever 13 316 Machined from mild car- Quenched and tempered.

Front Guide Bracket bon st ee l pla te .Seat

10 9 Hand Cocking Lever 37 182 Machined from mild car- Normalized.Rear Guide Bracket bon s t e e l p la te .

11 0 Hand Cocking Lever 3 22 6 Headed from screw s tock. Hot headed and annealedCap Screws

111 Auxiliary Hand Cocking 709 100 Cut from rolled plate. Annealed.Lever Low carbon s t e e l .

112 Auxiliary Hand Cocking 70 136 Dit to Annealed.Lever Ex ten sio n Cadmium pla ted .000 2".

113 Auxiliary Hand Cocking 40 20 3 Machined from screw Norm alized .Lever Coupling s tock.

1 U Auxiliary Hand Cocking 7 220 Machined from screw No rm ali ^d .Lever Bolt s tock.

115 Auxiliary Hand Cocking 4 250 Machined from screw Norm alized.Lever Bolt stock.

TABLE 2 ANALYSES OF SELECTED PARTS OF JAPANESE "BROWNING" MACHINE GUN(BMI #437 - CEE #2950)

P a r t Chemical S pe ctr oerarihic

N o. Name C P s Mn S N i Cr W Mo Cu Sn A l V** T i**

1 H o us i ng .80 .020 .023 .55 .33 .15 .07 <;oi .016 .2 9 .1 1 .009

8

9

A s s embl yB a r r e lB a r r e l

E x t e n s i o n

.60

.6 1

.012

.ou

.028

.ou

.4 2

.4 3

.32

.20

.17

.20

.1 6

. U

2.23

1.89

.011

.019

.2 4

.3 1

.ou

.065

.030

.053

12 B a r r e l B o o s t e r .64 .023 .023 .53 .47 .20 .12 2.08 .020 .2 8 .071 .012U Breech Lock .5 9 .026 .019 .4 8 .27 .17 .17 2.20 .017 .23 .057 .00815 Breech Lock Cam .71 .020 .022 .4 5 .28 .17 .21 .5 8 .017 .23 .090 .01318A Breech Lock Pin .6 4 • .025 .63 .53 .16 .12 1.85 .011 .23 .041 .00832 Bolt .62 .024 .021 .4 7 .27 .24 .17 1.70 .022 .26 .067 .01833 Bolt .70 .034 .019 .4 4 .30 .20 . 2 0 1.20 .016 .23 .042 .010

Decelerator

39 Bolt Release .76 .026 • .41 .30 .1 3 .07 2.10 .006 .20 .043 .011

40Lever Pin

AcceleratorAccelerator

.6 6

.6 8.020.034

.021

.021.4 7.4 4

.2 1

.29

.2 0

.2 1.19.1 1

2.05

1.85

.26

.008

.26

.27

.050

.054

.018

.028

.026

45Ul

Catch

Firing PinFiring Pin

#

.7 5

-*

.025

*

.016 .5 8.42. 30 ..37

.12

. U . U.192.05

2.08

.013

.021

.25

.2 6

.036

.066

.015

. 0 U .033Spring Con #

505357

tainer

SearCocking Lever

Extractor

.3 7

.6 7

.7 0

.023

.025

.025

*

.011

.015

.5 7

.3 7

.5 4

.37

.22

.32

3.70

.1 5

.2 1

1.54.1 8.0 8

.0 8

1.70

1.88

.1 1

.025

.012

.33

.22

.23

.12

.053

.045

.019

.ou

.015

6566

Recoil HousingMain Recoil

. 6 1

.7 3.031.020

.025•

.4 6

.2 8.2 4.2 3

.15

.0 5. U.0 9

1.84<£.01

.017

.006 ..2 4

-£.04.056.004 -

.015<.005

67Spring

.Secondary .8 1 .030 .037 .6 2 .3 4 .0 6 -£.03 <.01 .005 . U .092 .019

Recoil Spring

- 1 1



TABLE 2 (CONT.)

Part lemlca! SpectrocraDhicNo . Name C P S Mn S i N i Cr W Mo Cu Sn Al V** Ti*»

72 Spring Buffer .88 .038 • .5 2 .2 9 . 2 8 .23 .1 8 .009 .24 .068 .017Tube Head

75 Spring Buffer .6 7 .025 . 026 .4 2 .2 5 .1 6 .1 3 1.75 .016 .24 .080 .014Tube Seat

76 Spring Buffer .7 5 .038 .026 .7 0 .33 .13 .3 8 -<.01 .030 .29 .14 .014Rube Cover

78 Auxi l iary .7 7 .044 .056 .76 .37 .05 -c.03 <:.01 -<.005 .20 ~ .14 .006Buffer Spring

84 Back Plate .32 .025 . 024 •44 .26 .11 1.03 <.01 . 2 2 .023 .018.uock Bolt

86 Trigger Bar * * * .52 .32 .18 . 1 7 2.22 -C005 .16 .037 .014Extension

93 Automatic * * * .48 .25 3 .29 1.09 <.01 <.005 .33 .058 .010Trigger

94 Automatic * * # .30- .25- 3 . 0 0 - .90- <^.01 .10- .45- .05- < . 0 0 5Trigger .40 .35 3.50 1.10 . 2 0 .5 5 .15Retainer

95 Automatic * * .48 .26 3 .3 0 1.02 <.01 <.005 . 2 1 .098 <C.005

Trigger Piston

* Insufficient sample for analysis.

** Vanadium ( .004) except where shown. Titanium ( .004).

TABIE 3. PHYSICAL TEST DATA* (BMI #437 - CEE #2950)

Per Cent Per Cent l i e Id Tensile Impact

Part Type Reduction Elon gation , Stren gth, Str eng th, Charpy V- Hard-

No. Name S te el ef Area In 2" p . s . l . p.s . i . Notch, nessFt. Lbs.

1 A Housing SAE 1080 29.2 14.6 91,500 136,000 Rc*21Plates

B 40 17.8 89,000 133,0008 A Barrel 50.3 23 102,500 134,000 31 Re'29

B 2-1/456 49.8 23 112,000 134,000 33Tungsten

* Standard .505" x 2" A.S.T.M. specimens.

-12



py T.TRT

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