US2365389A

US2365389A - Firearm

Info

Publication number: US2365389A
Application number: US417753A
Authority: US
Inventors: Marriner A Browning
Original assignee: J M & M S Browning Co
Current assignee: J M & M S Browning Co
Priority date: 1941-11-04
Filing date: 1941-11-04
Publication date: 1944-12-19
Anticipated expiration: 1961-12-19

Description

Dec. 19, 1944. M. A. BROWNING F IREARM Filed Nov. 4, 1941 2 Sheets-Sheet l 2] Wm MRRJNEE A. 5ROWN /NG fluozm a,

Dec. 19, 1944. M. A. BROWNING 2,365,389

FIREARM Filed NOV. 4, 1941 2 Sheets-Sheet 2 gal/um MARIA/ER 14.5220 WMNG Patented Dec. 19, 1944 Marriner A. Browning, Ogden,

Utah, assignor to J. M. & M. S. Browning Company, Ogden, Utah,

a corporation of Utah ApplicationNovember 4, 1941, Serial.No.417,753

recl ims,

The present invention-relates to repeating firearms and more particularly to the type of firearm shown and described in the copending appli'cati'on of ValAJBrowning, Serial No. 401,602, filed June 9, 1941. v p r y In said application, the firearm disclosed is of the blow-back type-that is, the recoil mass is in axial alignment with the cartridge, and, upon explosion of the cartridge, it moves rearwardly while retaining such axial alignment. In the firearm disclosed in said application, the recoil mass is made of a plurality of parts adapted to successively move rearwardly and then forwardly and, in so doing, to absorb and disintegrate the recoil shock.

The object of the present invention is to provide in a gun of the above-indicated type means cooperating withthe' recoil mass, which means further assistin absorbing and disintegrating the recoil shock.

Another advantage is that the'additional means disclosed in the present application provides additional resistance to the pressure created upon firing without increasing the weight of the recoil mass.

A further advantage is that the additional means is so constructed as to provide a-temporary retarding action which impedes rearward movemerit of a part ofthereoil mass during a portion of the movement-of another partof' the recoil mass and wherein the retarding or looking action maybe readilyvaried by varying the construction ofthe means forproviding such locking androtarding-action. v

Other objects willbe' in pointedout more in detail hereinafter:

The invention accordingly consists in the features of construction, combination of elements, and arrangement of parts which will be' exemplified inthe construction hereafter set forth and the scope of the application of which will be indicatedinthe-appendedclaims v In the accompanyingdrawings:

Figure 1' is a sideelevationalviewof a" repeating firearm embodying the invention herein;

Fig. 2 is a sectional view taken generally longitudinallyandvertically through the receiver and showing the various p'arts'in theirfiring position;

' Fig; 3 is a viewgenerally similar to Fig. 2, but showing the parts in position at the completion of the recoil operation;

Fig. 4' is VB, plan View partly in section to show the manual cockingmeans; and

- Fig. 5 is a view t'aken generall along the line 5-5 of F-ig. 3.

part obviousand in part Referring to thedrawings, the gun comprises generally a receiver aabarrel B, andstock C in which there is located a recoil housing I) which alignment with the barrel and receiver. Located withinthe receiver A and extending intothe housing D is a recoil mass E comprising a plurality of parts which, upon the firing of the gun, separate slightly from one another and move rearwardlyto compress a recoil spring F in the housing D; the spring then expanding and moving the recoil mass forwardly. More specifically, the receiver A comprises a tube H] of relatively light material provided at its forward end with aninternal thread I2 for securing the barrel and atrit's after end with an external thread it for securing theenlarged end of the housing D. The-receiver is furtherprovideo at one side withanopening It through which the cartridges are ejected andin its base with a forward loading opening 1'8 and an after trigger opening 20. Located within the base of the receiver is a trigger plate 22 having a particylindrlcal lower sur ace conforming. to the internalperiphery of the tube HI. The trigger plate has, on opposite sides of its center line, raised lands 2'4 provided'with flat top surface 23' upon which a portion of the TECOlIlllQSs E is slidably mounted. a Referring now to the recoil mass E, it comprises a breech block 26,. an extension bloclr 30, and a follower block arranged and are so designed that upon the firing of the gun the parts will successively move to reis arranged in axial coiliposi'tion with the extension and follower block definitely separating'from the breech block. In the present embodiment, this separation is assured by temporarily retarding the initial rearward movement of thebreech block by locking and cushioning. means which comprise a lockin block 28 anda spring. I The locking blockor member 28 inturn isrestrainedin. looking position b the extensionblook until-the latter has definitely separated from thebreechblock. Upon firing the gun, the several: blocks of. the recoil massare successively stopped in their rearward movements whereby the shock or recoil is smoothed out1ord1stributedand the spring 501 assists in cushioning the shock, as hereinafiter described. Further, this spring serves to ease or distribute the shock whenthebreech block rebounds to its foremost position against the rear end Of the barrel.

Referring particularly to the breech block, it has a parti-cylindrical upper-surface 34 having a 32. These parts are successively cushioning means is positioned.

rounded portion about which the member may,

fulcrum or rock.

ing an upwardly and forwardly extending camming and locking shoulder42iand a downwardly and forwardly extending camming shoulder 44.

Locking block 28 further includes a longitudinally extending bore openat its forward end At its after end, block 28 terminates in a Wedge-shaped enlargement 29 havfollower block 32 also terminates in a portion 82 to seat one end of the recoil spring F; the other end of the spring abutting a buffer (not shown) at the rear end of the housing D.

When the parts are in their forward firing positions shown in Fig. 2, the breech block is forced against the rear end of theb-arrel, and the breech block, extension block, and follower block are forced together by the recoil spring F so that the three blocks'act as an integral mass to close the breech. Furthermore, the cushioning spring 58, acting through the pin 48 and the locking block 28, resiliently urges the breech block against the rear end of the barrel so that the force of this spring is added to the weight of the breech block, extension block, and follower block to properly resist rearward movement of the to receive a pin 48 and the compression spring 50. The spring 50 normally tends to urge the pin 48 out of the bore, but the-latter is retained by a. pin 52 extending transversely of the bore and through a U-shaped recess 54 in the pin. Also,

the channel 38 of the breech block and is not otherwise connected thereto. VVhenthe parts are in firing position, the lockingblock 28 assumes the lockingorlatching. position shown in Fig. 2 with theenlargedafter end 23 0f the block partially projecting through an opening 58 in the top of the tube. I D with the upper camming and locking surface42 spring, pressed into engagement with the rear wall of the opening 58 which constitutesalocking stop 60. v The locking block' described positio-niby an abutment 62 extending forwardly fromtheextension block 30 and positioned between rearwardly projecting ears 64 of the breech block. The extension block and breech block are connected at this point by a lost motion connection comprising .a pin 66 extending through aligned openingsin the breech block ears 64 and an elongated slot 58 in the abutment 62. The forward end of abutment 62 is formed to provide a downw 'rdly and forwardly extending cam 10 which cooperates with thecam shoulder 44 of block 28 to urge the latter, when the breech block reaches the end .of its forwardmovement, to latching or breech block retarding position and tothen restrain the locking block in said position. 1 I To guide the locking block there extends forwardly from the} abutment 62 a rectangular tongue 12 seated within a corresponding rectangular recess 14 in the breech block 26 and upon which the afteren'd of theblock 28 rests as the parts move to andfrom firing'position.

Rearwardly of the abutment 62 the extension block has a p arti-cylindrical collar l6 having a radius corresponding to that'of the tube ,ID to permit it toslidably fit therein, and rearwardly of the collar 16 this-radius is decreased to that of the tube D for'slidably guiding the extension block therein. The extension blocl; 3D is further cut away to provide a flat base 80 extending substantially its full length and adapted to overlie and slide on the lands of the trigger plate.

Referring now to-the follower black, this is wholly contained within the housing D just rearwardlyof the extension block 30, and, if desired, it could be an integral; part thereof. However, for simplicity in manufacture, these parts are made separate but with a telescoping connection 11 to maintainthem. in proper alignment. The

2 8.is retained in the aforeing cartridge at the time of firing.

blow-back action such advantage in that it breech block against'the pressure of the explod- It may be stated here that the force of this spring is added to the inertia of the recoil mass to properly resist the rearward motion of the breech block upon firing because, particularly in a light gun. the inertia mass itself may not be of sufficient weight especially where the gun has a straight as is here shown. The operation, upon firing of the gun, is as follows: At the instant a cartridge in the firing chamber is fired, the power gases generated initially act upon the breech block, extension block, and follower block as though they were one integral mass, and this mass is driven violently to the rear against the force of the recoil spring F. However, upon such rearward movement, the cushioning spring 50 retards the movement of the breech block, thus; causing the breech block to lag behind the extension block so that these blocks will separate to the extent allowed by the lost motion connection comprising the pin 66 and the slot 68, and when these blocks so separate, the lug 62 of the extension block rides from underneath the locking block 28 with the result that the locking and cushioning means assumes the position shown in Fig. 3 and in which position the spring acts as a cushion between the breech block and the extension block and, thereafter, the extension block will move rearwardly at the same rate as the breech block. Furthermore, due to the lag exerted on the extension block through the breech block, the follower block will separate slightly from the extension block. Rearward travel of the follower block is limited by the impingement of that blockagainst the buffer (not shown) fixed in the. rear end of the recoil spring tube D. ..The extension block then stops against the forward end of the follower block, and then the breech block stops against the forward end of the extension block. Thus, the several blocks of the recoil mass are separately and successively stopped in their rearward movement, these stoppages being effected in an almost imperceptible period'of time but they'are spaced apart sufficiently in time to permit of a smoothing out or distribution of the shock of recoil over that which would result should such movement between the several parts not be permitted. It may be that the extension block will rebound forwardly be-- fore the breech block completes its rearward movement. The cushioning spring .50 has the plays an effective part in smoothing out the shock of recoil, it being observed that when the breech block moves rearwardly against the stopped or rebounding extension block, the spring 50 will be compressed so as to give a cushioning action which assists in neutralizing the shockefiect. Itcis. understood that themecoilx. spring E, is. compressed during; recoil until: the: follower block; strikes the buffer, and then that spring-,forcessthe; reco-ilmass forwardly into. the firing; position; shown in Fig; 2. During such; forward: movement, the extension. block is maintained in spaced relation to the breech block by the'cushioning spring EBI andIthelock-r ing; block 28,. and the follower block will: lag slightly: behindithe; extension. block; As the-re ooilamass: reaches its foremost-position, t'hfixfOY- ward} end. of; the; breech block first comes into contact with the breech; parto-f. the barrel and then the-. 'extensionblockwill come against the rearendof the-breechblock; but before the ex' tension; blockstrikes the rear. end oi. the now stopped breech. block; the. cam surface I'D: will.

cam the: locking; block to the" locking position shown .in-, Fig; Z'and the'lug. 62 will ride beneath the locking block to: restrainitin locking position. Atytheiorwand: stopping point of; the action, the cushioning spring 50 serves toirorr out or' distribute the shock, itbeing observed that the forward movement or: the extension block,

afterthe breech block has been. stopped against the'sendofrthe barrel, is; cushioned bythis spring.

It will thus be observed that the locking and cushioning means serves Various functions including that of assistingtheinertia mass to: resist the rearward'movementof the breech block againstthe; pressure; of theexploding cartridge at-the time oflfiring, insuring that the extension block be held in. spaced relation to the breech block. during recoil: and forward movements of the rec-oils. mass, and assisting in. cushioning: the shock at both the. rearward" and. forward limits of. movements. of the: recoil: mass;

Withthe foregoing arrangement, it w ll be seen that. therblock 28 not only functions. asa locking. means, but also: as a crushioning'means. Because of, this, the weight" of the parts of the inertia mass maybe considerably reduced and thelossinweightccompensated for by. the locking action of block 28-. and? the strength of spring 5!) within same. It is apparent that the locking action. maybe varied by increasing or decreasing theangleof the cams d2, 44, and it as wellas by" varying the length of the locking block 28.

As the extent of: manual rearward; movement of. the breech block'from firingposition is limited by the locking block and" extension block, in order to manually cock'the gun it is necessary that means he provided for" initially separating the extensionblock from the-breech block. To ac ccmplish this (see Eig. 4), the breech block 26. is; provided, in transverse alignment with the cartridge ejecting opening, IS, with a T-shape'd guide groove 81 extending from the forward end of the block through approximately one-half the length thereof and is then providedwith. an enlarged-bore- 8-3 terminating at the" rear'end of the breech blockin a reducedbore tti. Located withinthe bore? 83 isa pin 8:1 having a reduced extension 89 extending through: the reduced bore 85; Positioned on the reduced extension isa: spring 9I- which normally tendsto urge the pin forwardly and outwardly of. the recess. The pin is normally maintained in place by a slidemember 93 of. T cross section which fits within the T guidegroove BI. The. forward end of the slide 9.3 carries an operating handle 85 in whichthere is slidably mounted a retaining pin 9'! of greater length than handle 95 and having an. enlargedrcollar SSintermediate 0f; its ends. The pin is normally urged inwardly towards the breech block-bye spring- I 0h positioned between the;=col1a1-. and; a cover In3; whereby the; pints inner endis: positioned within i av groove I (I5 paralle in l the T guideandaalsocut in the breech blo.ck.. Thecover I03 is -in1 the form of a washer threaded. into-arecessinthe handle 95 and in which recess the,- spring. I U I ishoused.

With. this arrangement, upon .moving' the handle 95 rearwardlmthehandle may-move-through the length of the slot I05 to force the pin 81- rearwardly. The; rear-ward end.- of the pin, will thencontaoti the extension; block, .forcing itrearwardly' and. thereby moving the abutment 62 from! under the locking block so as to release same. After thB'IOQKiDg bIOCK; has been released, the pin 91'willthen. abut. the. rear end of the slot I 95, to, simultaneously; draw the .br.eech. block rearwardlyr. Upon? release. of: the parts, handle 95-will be moved; to'its forwardpositon by: spring 9|; For convenience inassembly, it will beseen thatthepinzfi'l; may be. pulled outwardly to permittheremovatofthe. slide 93 from the guide 8| to allovwthe; recoil mass to be withdrawn through the rear of the. tube I:0-upon removal of, the-stock C;

In order to firethecartridge, the recoilmass is provided! witha bore- 84=- in which there is mounted-at firing: pin .86, which: pin terminates at its: forwardlend. in. a firing: point 88: adapted to projectthrough a reduced bore 90 in theforward wall of the breech block to contact the cartridge. The rear endof thefiring pin carries a reduced: portion 9:! on which there is mounted azspring.94,.whichrspring'normally tends to urge. thefir-ing pin: towards firing position. The: operation. of the firing. pin is controlled by a, firing. mechanism. comprising, a sear conadapted to extendthrough a. rectangular metal slide I94 secured to a Wooden U'-shaped holding member Hi6, whichlmember m turn is secured to the-barreliBl Toretain the magazineiinplace, its rear wall is-providedwithan opening I98 for receiving the latching hook I09 of alatch member I-IOl, Asqindioatedr the latch member comprises an elongated; arm with the'hook: U39 at its lower end: and an opening lill'tat its upper end for pivotally mountingthe latch on a. pin I I2 bridging;

a slot in the forward end, of the. trigger plate. The latchisi normally urged: into latching position bya: plunger II3positi0ned; in abore in the triggen plate and. normallyurged. towards latch-. ing position by a spring I I5. Iomanually release. thelatch I l 0, its; lower end may likewise be provided with afingerpicce IIT.

Also: associated with the. latch III] is a second latch. Ildywhich latch functions both as a stopopen: latch. and as an; ejecting member. More particularly, latch; [Mt includes a depending arm LI 6; providedvwith a vertical, slot I I8: for pivotally mounting iton thepivot pin I I2. The lower end of the arm I16: further carries a laterally extending pin I720 extending througha slot I22 in the memberxl I0; In this way; the latch I I4 is mountedtfor. pivotalimovement simultaneouslywiththe latch H0, but is also capable of vertical movement relative thereto. Carried on the upper end of the arm H6 is a forwardly extending arm I24, and extending upwardly from this arm is a projection I26. The projection I26 normally lies, when the top latch is in lowermost position, within a groove I28 provided in the base of the breech block and also lies in the path of a cartridge withdrawn from the barrel by the usual ex-' tractor I30.

With this construction, during the firing operation, the upper end I26 of the stop latch functions as an ejector for throwing the cartridges out through the ejecting opening I6. However, as the last cartridge is fed into the gun, the follower I32 of the magazine will engage beneath the forwardly extending arm of the stop latch. As a'result, when the breech block has moved rearwardly of the ejecting end I26 upon the next recoil, the follower will move the stop latch vertically and into the path of movement of the breech block. As the breech block then tends to return, it will engage the end I26, pivot the stop latch, and simultaneously pivot the latch III], whereupon the cartridge magazine will be released and drop out of the loading opening. I

Following a reloading of the gun, the stop latch may be moved downwardly by grasping a fingerpiece I 2I provided at the bottom of the arm II6 to release the breech block and recondition the gun for firing operation.

As many changes could-bemade in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the language used in the following claims is intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said to falltherebetween.

I claim as myinvention: I

1. In a firearm, a receiver having a stop shoulder, a recoil mass mounted for sliding movement in the receiver and comprising a plurality of parts, one of which being a breech block adapted to close the firing chamber and another part being an extension block adapted to separate slightly from the breech block upon recoil, a recoil spring normally urging said parts into engagement with one another and said breech block into breech closing position, a locking block carried by said breech block for pivotal and longitudinal movements relative thereto and having a locking shoulder engaging said stop shoulder when the breech block is in breech closing position, a cushioning spring between said locking block and breech block and normally urging the locking block rearwardly of the breech block, and means on the extension block for holding the locking block in stop shoulder engaging position when the extension block is in foremost position, said means being released from said locking block when said extension block separates from said breech block upon recoil when the gun is fired.

2. In a firearm, a receiver having a stop shoulder, a recoil mass mounted for sliding movement in the receiver and comprising a plurality of parts, one of which being a breech block adapted to close the firing chamber and another part bein an extension block adapted to separate slightly from the breech block upon recoil, a recoil spring normally urging'said parts into engagement with one another and said breech block into breech closing position, a locking block carried by said breech block for pivotal and longitudinal movements relative thereto and having a locking shoulder engaging said stop shoulder when the breech block is in breech closing position, said locking shoulder being upwardly and forwardly inclined whereby when said locking block'is released and said breech block'recoils said locking block is cammed inwardly out of engagement with said locking shoulder, a cushioning spring between said locking block and breech block and normally urging the locking block rearwardly of the breech block, and means on the extension block for holding the locking block in stop shoul-' 'der engaging position when the extension block is in foremost position, said means being released 7 from said locking block when said extension block separates from said breech block on recoil when the gun is fired.

3. In a firearm, a receiver having a stop shoulder, a recoil mass mounted for sliding movement in the receiver and comprising a plurality of'parts, one of which being a breech block' adapted to close the firing chamber and another part being an extension block adapted to separate slightly from the breech block upon recoil, a recoil spring normally urging said parts forwardly into engagement with one another and said breech block into breech closing position, a locking block carried by said breech block for pivotal and longitudinal movements relative thereto and having a camming and locking shoulder engaging said stop shoulder when the breech block is in breech closing position, and a cushioning spring between said locking block and breech block and normally urging the locking block rearwardly of the breech block, said extension block havi. a cam surface for camming said locking block into engagement with said stop shoulder as said extension block moves forwardly into engagement with said breech block after the latter reaches its breech closing position, said extension block further having an abutment for holding the locking block in stop shoulder engaging position when the extension block is in foremost position, said abutment being released from said locking block when said extension block separates from said breech block upon recoil when the gun is fired.

4. In a firearm, a receiver having a stop shoulder, a recoil mass mounted for sliding movement in the receiver and comprising a plurality of parts, one of which being a breech block adapted to close the firing chamber and another part be ing an extension block adapted to separate slightly from the breech block upon recoil, a recoil spring normally urging said parts forwardly into engagement with one another and said I breech block into breech closing position, a locking block carried by said breech block for pivotal and longitudinal movements relative thereto and having a wedge-shaped rear end providing an upwardly and forwardly inclined locking shoulder adapted to engage said stop shoulder and a downwardly and forwardly inclined camming surface, and a cushioning spring between said locking block and breech block and resiliently urging said breech block in breech closing position when said locking block is in stop shoulder engaging position, said extension block having a cam adapted to engage said camming surface of the locking block to cam the latter into stop shoulder engaging position as the extension block moves into agerness vits finai "forward position and also having "an engagement with one another and said breech :abutment'for holding said locking block in said position when said extension block is in its foremost-position.

"5. In'afirearm,"areceiver having a stop shoulder, a recoil'inass'mounted for sliding movement in the receiver and comprising a breech block adapted to close'the 'firin'gchamber and an ex- 'b'lock in't'o breechclosing position, a locking block tension block adapted to-separate slightly from the breech block uponrecoil, said breech block and a camming surface engageable with said camming surface of said extension block, a pin positioned within a bore of said locking block and having its forward end engaged in said recess, and a cushioning spring within said bore between said pin and locking block, said abutment holding said locking block in operative position with said locking shoulder in engagement with said stop-shoulder when said recoil mass is in firing position and said camming surface of said extension block being arranged to cam said locking block to said operative position while said extension block is moving forwardly to final position after said breech block has moved to breech closing position.

6. In a firearm, a receiver, a recoil mass mounted for sliding movement in the receiver and comprising a breech block adapted to close the firing chamber and an extension block adapted to separate slightly from the breech block upon recoil, a recoil spring normally urging said parts into engagement with one anotherand said breech block into breech closing position; cushioning and locking means comprising a locking block carried by the breech block for pivotal and longitudinal movements relative thereto and a cushioning spring between said locking block and breech block and normally urgin the locking block rearwardly of the breech block; said cushioning and locking means being positioned between said breech block and receiver when the breech block is in firing position whereby initial recoil movement of the breech block i retarded when the gun is fired, and said cushioning and locking means being positioned between said breech block and extension block after the looking block is disengaged from the receiver whereby said breech block and extension block are resiliently maintained in separated relation and said cushioning spring cushions the shock upon recoil, and means on the extension block for holding the locking block in breech block retarding position when the parts are in firing position, said means being released from said locking block when said extension block separates from said breech block upon recoil when the gun is fired.

'7. In a firearm, a receiver having a stop shoulder, a recoil mass mounted for sliding movement in the receiver and having a breech block adapted to close the firing chamber and an extension block adapted to separate slightly. from the breech block upon recoil, said extension block having a camming surface, a recoil spring normally urging said parts of the recoil mass into carried by said breech block for pivotal and longitudinalmovement's relative thereto and engageable with said stop shoulder whenthe recoil mass is 'in firingpos'ition andengageablewith said cairn ming-surface after the lo'cking *block has been released from tneflockin'g shoulder, said camniing surface being arranged totem said locking block into engagement with said stop shoulder while tlre'extension blockis moving forwardly into final position after the breech block hasbeenmove d forwardiyto breech closing position, and a cus'h-, ioning spring between said locking block and breech block and normally urging the locking block rearwardly of the breech block.

8. In a firearm, a receiver having a stop shoulder, a recoil mass mounted for sliding movement in the receiver and comprising a plurality of parts, one of which being a breech block adapted to close the firing chamber and another part being an extension block adapted to separate slightly from the breech block upon recoil, a recoil spring normally urging said parts into engagement with one another and said breech block into breech closing position, a locking block carried by said breech block for pivotal and longitudinal movements relative thereto and having a locking shoulder engaging said stop shoulder when the breech block is in breech closing position, a cushioning spring between said locking block and breech block and normally urging the locking block rearwardly of the breech block, and means on the extension block for holding the locking block in stop shoulder engaging position when the extension block is in foremost position, said means being released from said locking block when said extension block separates from said breech block upon recoil when the gun is fired, said extension,block further having a forwardly facing surface against which the rear end of said locking block is engaged after said locking block is released from said stop shoulder.

9. In a firearm, a receiver having a stop shoulder, a recoil mass mounted for sliding movement in the receiver and having a breech block adapted to close the firing chamber and an extension block adapted to separate slightly from the breech block upon recoil, said breech block having a rearwardly facing surface and said extension block having a forwardly facing camming surface and an abutment therebehind, a recoil spring normally urging the recoil mass into breech closing position, a locking block carried by said breech block for pivotal and longitudinal movements relative thereto and having a camming and locking shoulder engaging said stop shoulder when the breech block is in breech closing position, said locking block further having a camming surface engageable with said camming surface of said extension block during reciprocation of the recoil mass, and a cushioning spring between said locking block and said rearwardly facing surface of said breech block and normally urging the locking block rearward- 1y of the breech block, said cam surface on the extension block being arranged to cam the locking block into stop shoulder engaging position as adapted to close the firing chamber and an extension block adapted to separate slightly from the breech block upon recoil, said extension block having an abutment with a downwardly and forwardly inclined camming surface at its forward end, a recoil spring normally urging said parts of the recoil mass forwardly into engagement with one another and said breech block into breech closing position, a locking block carried by said breech block for pivotal and longitudinal moveand forwardly inclined locking shoulder adapted to engage said stop shoulder when said breech ,ments relative thereto and having an upwardly