Firearm

This invention relates to firearms and parts thereof, and in particular, although not exclusively to gas operated automatic guns, although it may also be used with semi-automatic guns.

Automatic guns are well known and the term is applied to a gun in which, when a trigger 'is pulled, a plurality of cartridges are fired serially for as long as the trigger is held or until the last cartridge is fired. Semi-automatic guns are similarly well known and the term is usually applied to a gun which, when a trigger is pulled, fires a cartridge subsequently ejects the cartridge, cocks the bolt and chambers a next cartridge automatically but does not fire said next cartridge until the trigger is released and again pulled to repeat the cycle. Automatic and semi-automatic guns are generally of three different kinds namely, recoil operated, blow-back operated or gas operated and the present invention relates to the latter form of operation.

Automatic and semi-automatic guns are well discussed in literature and examples are "Small Arms of the World" by W. H. B. Smith, tenth edition completely revised by Joseph E. Smith published by Stackpole Books, Harrisburg, Pennsylvania, U.S.A., and Janes Infantry Weapons 1977 edited by Dennis H. R. Archer published by Janes Publishing Company, and a known type of gas operated, automatic gun is the United States 7.62 mm NATO M.60 machine gun described at pages 695-699 in Small Arms bf the World and Pages 332-337 of Janes Infantry Weapons and . the 5.56 mm AR18 rifle described at page 656 in Small Arms of the World and pages 229-231 of Janes Infantry Weapons.

A gas operated gun, such as the AR18 has a receiver housing a bolt/bolt carrier assembly which is urged toward a barrel by a drive spring and actuated by a trigger through the intermediary of a sear. A radial drilling through the wall of the barrel is provided at a predetermined distance along the barrel length and externally in cooperating with the drilling is a gas piston and cylinder assembly. In operation the bolt/bolt carrier assembly strips and feeds a cartridge from a magazine into a feed area within the receiver and the bolt drives the cartridge over a feed ramp within the normally provided barrel extension to chamber the cartridge: The bolt is usually then rotated into a locked position so that the cartridge is securely held within the chamber. Because the bolt/bolt carrier assembly are slidably and rotatably movable with respect to one another and the firing pin is carried by the bolt carrier assembly, final forward momentum of the bolt carrier assembly rotates and locks the bolt as it drives the firing pin into the cartridge to thereby discharge the cartridge. Gas is produced by the firing action of the cartridge, which gas enters the radial drilling once the bullet has past the drilling and enters the gas cylinder whilst the bullet is still within the barrel. Of course, once the bullet leaves the barrel the gas is dissipated. The cylinder is arranged to be the movable part and the cylinder is connected to the bolt carrier assembly by a rod so that as the cylinder fills with gas it is driven by the gas, the bolt carrier is driven rearwardly thereby unlocking the bolt, extracting the spent cartridge, ejecting the same and cocking the gun for. a further series of operations. A further, similar, cycle is then produced for as long as the trigger is squeezed and of course for as long as there are cartridges to provide the gas discharge. It is to be noted that the movable cylinder does not have the same length of travel as the bolt carrier assembly.

The AR18 rifle along with several other automatic weapons fires from a closed bolt position which means that the bolt/bolt carrier assembly are all the way forward and a round has been chambered by the preceding cycle so that when the trigger is pulled only the hammer or other light weight firing mechanism moves; the bolt and carrier assembly do not move until after firing takes place and there is no consequential motion or force applied to the gun before the instant of firing. This is in distinction to a gun which fires from the open bolt position (such as. an M-60 machine gun) where the bolt/bolt carrier assembly are held back behind the feed area by the previous cycle being interrupted and the bolt carrier being caught by a sear before the bolt/bolt carrier assembly are driven all the way forward by the drive spring. Thus, initially no cartridge has been chambered and when the trigger is pulled the bolt/bolt carrier assembly is released and driven forward by the main spring to then chamber and fire the cartridge. When firing from the open bolt position there is a rearward force applied to the gun before the instant of firing due to the reaction of the drive spring in pushing the bolt carrier forward.

In the cycle of operations the bolt carrier travels to a rearward position thereby overtravelling the feed, e.g. the magazine delivery port, so as to permit a further round to be fed and chambered.

In known gas operated guns it is normal for the bolt carrier to impact the rear wall of the receiver to limit the extent of rearward travel and in many known guns, such as the M60 the impact is through the intermediary of a buffer.

By the term "buffer" as used herein is meant a means which is interposed between the bolt carrier assembly and the stop to rapidly retard the bolt carrier and which has a force at least twice greater than that of all the other combined spring force averages.

Thus, in known gas operated guns, not only is there a recoil from the gun when the cartridge fires but there is also a recoil when the carrier assembly strikes the rear receiver wall even if through the intermediary of a buffer. The effect of such recoil upon a user of the gun is that whilst the first round may have been on target, subsequent rounds tend to drive the barrel of the weapon upward so that shots are fired above the target. It must be remembered that such automatic weapons usually fire of the order 6-12 rounds per second and it takes some time, of the order of 1-2 seconds before the user of the weapon is able to compensate for the recoil effect and bring his aim back on to target. Such weapons due to loss of control by a user tend to be inaccurate.

Although the loss of control has been substantially mitigated in both blow-back and recoil guns by providing a softer recoil, the solutions employed in those guns have not been thought applicable to gas operated guns because of the operational differences between the types of guns. The recoil operated gun has fallen into disfavour due to its complexity in requiring both the barrel and bolt/bolt carrier assembly to be moved backwards so as to recock the gun and blow-back guns, although still in use by infantry are operable only with low powered, short range cartridges. For these reasons it is highly desirable that the gas operated gun which is generally preferred by . present day infantry due to the fact that it is not so susceptible to fouling by mud and grit etc., be provided with improved accuracy when operating in a fully automatic mode.

In a gas operated gun numerous attempts have been made to lessen the effect of the bolt carrier striking the rear receiver wall so as to provide zero restitution. The term "restitution" means that proportion of energy from an impacting mass which is returned to that mass upon striking a fixed, solid object. Thus, if a steel bolt carrier strikes a steel rear wall of the receiver most of the energy of the impacting carrier assembly will be returned to the carrier in the opposite direction by the rear receiver wall. In such an instance there is thus 100% restitution, i.e., very high recoil and the AR18 is an example.

In the M16 rifle (described at pages 650-653 in Small Arms of the World and pages 226-228 of Janes Infantry Weapons) an attempt has been made to reduce restitution by providing a buffer carried by the rear of the bolt carrier assembly so as to absorb some of the energy of the impacting bolt on the rear receiver wall. The buffer is compressible between the rear receiver wall and the rear of the bolt carrier assembly. Although the coefficient of restitution of the M16 is considered to be low, it is still found that a significant recoil is caused by the rear.receiver wall being impacted by the buffer/bolt carrier assembly.

The recoil effect on a gas operated gun is normally considered less than that of a bolt action gun which, although not automatic, contains many similarities with a gas operated gun. In this respect they both have a locked and rigid structure that tries to deliver the cartridge impulse during "bore" time. The lighter recoil has been attributed to the gas in the cylinder not only driving the moving member, be it the cylinder or piston, rearwardly but also the gas driving the front wall of the fixed member in a forward direction. Thus, gas operated guns tend to have a "softer" action than the aforesaid bolt action gun. Nonetheless, the effect of recoil is still as described above, i.e., the user loses aim after the first shot has been fired and it is evident that the cause of the user losing aim is because of the number of differing recoil actions that occur which are experienced by a user as a series of separate sharp blows. Various attempts to overcome recoil have been made and reference may be paid to "Hatcher's Note Book" by Julian S. Hatcher, published in the United States of America by the Telegraph Press, 3rd Edition, 2nd printing April 1976, page 262 et seq.

Because of the action of recoil on the controllability of known gas operated guns the hit probability of such guns is poor. Attempts to improve the hit probability of such gas operated guns include 3 shot burst limiters, high rate rifles that fire 3 to 4 shots extremely quickly so that the gun does not have time to move off target and duplex or triplex cartridges that fire 2 or 3 bullets with each shot. None of these devices have proved successful and have merely shown the desperation of designers to improve the accuracy of a gas operated automatic gun. Our copending European Patent application No. 54088 is directed to this problem and attention is directed thereto.

Known bolt operating assemblies are usually of two types, namely a bolt carrier type, to which a first feature of the present invention belongs or an operating rod type. In the latter type the bolt and operating rod are each separately guided in the receiver and the operating rod extends forward of the breach (an example is the M60). In distinction the bolt carrier type has the bolt contained within the carrier and the carrier alone is guided by the receiver and usually no part of the assembly extends forward of the breach (an example is the M-16). To improve the controllability of a firearm as disclosed in our European Patent application No. 54088, it is desirable to extend a part of the carrier forward of the bolt to improve guiding, provide drive spring room and increase weight without increasing receiver cross-section or length, but known extended bolt carriers tend to be of complex construction.

It is an object of a first feature of this invention to provide a bolt operating assembly of the extended bolt carrier type which is simple to produce and a gun incorporating the same.

According to an aspect of this invention there is provided a bolt carrier assembly for a gas operated gun including a housing means for supporting a bolt, a P cross-sectionally shaped member having the longest side of the P shaped member secured to the housing means, said P shaped member being forwardly extended with respect to the bolt to be, in operation, adjacent the gas cocking system which is provided a predetermined distance along the barrel, and a main drive spring located alongside the wrapped-over portion of the P shaped member which is arranged to provide motion to the housing means and P shaped member.

Preferably, the housing means is a block having a bore within which the bolt is reciprocally arranged and conveniently the block is shaped to provide a bearing surface upon which reciprocal motion thereof is permitted.

Advantageously, sear contacting lugs are provided through the P shaped member and the housing means, and preferably two lugs are provided one passing through the wrapped-over portion of the P shaped member and the other housing through the planar portion of the P shaped member. Advantageously, the block has a downward extension substantially the same depth as the lugs to ensure that as the block travels rearwardly a cartridge being fed by a magazine is not contacted by the lugs.

Preferably, a closure member is provided at the end of the P shaped member remote from the housing means, and advantageously, said closure member is arranged to support one end of the main drive spring. Conveniently, an anti-bounce weight is mounted in the wrapped-over portion of the P shaped member and preferably said anti- bounce weight has a chamfer at one end which is engageable between the wrapped-over part of the P shaped member and one of the sear contacting lugs and the remote other end of the anti-bounce weight is attached to a compression spring which abuts the closure member, whereby the spring is compressed by the anti-bounce weight when the block and P shaped member combination are suddenly retarded.

Conveniently, a cam surface is provided on the side wall of the block for cooperating with a bolt cam pin. Advantageously an aperture is provided in the opposing side wall of the block to the cam surface to facilitate removal of said cam pin.

Advantageously, a notch is provided in the top of the P cross-sectionally shaped member adjacent the closure member which is suitable for engagement by a cocking means.

In a preferred embodiment a cartridge extractor claw is provided in a part of the wall of the bolt and a portion of said extractor claw is located within said bore to be substantially flush with the outer surface of the bolt, and said extractor claw is pivotally mounted and spring loaded such that an opening in the claw is engageable with a cannelore on a chambered cartridge and that in operation when the bolt is driven rearwardly the claw withdraws said cartridge.

In said embodiment a spring loaded ejector is provided on an opposing side of the longitudinal axis of the bolt to the extractor claw and the combination of claw and ejector are arranged to provide lateral impetus to be a de-chambered, spent cartridge.

According to another aspect of said invention there is provided a gas operated gun having a receiver, a rear wall of said receiver, guide rail means within said receiver for slidably supporting a housing means for a bolt forming part of a bolt carrier assembly a P cross-sectionally shaped member having the longest side of the P shaped member secured to the housing means, said P shaped member being forwardly.extended with respect to the bolt to be, in operation, adjacent the gas cooking system provided a predetermined distance along the barrel, and a main drive spring located alongside the wrapped-over. portion of the P shaped member arranged to provide motion to the housing means and P shaped member.

Preferably the main drive spring is supported on a guide rod and constrained between a closure member at one end of the P shaped member remote from the housing means and a tubular collar which is slidable between predetermined limits on the opposite end of the guide rod. Conveniently, the rear wall of the receiver is slidably positionable and mounted internally of the receiver on said rear wall is a lug arranged to cooperate with said tubular collar and on which said collar is normally mounted in use, wherein handle means external of the receiver are provided to slide said collar from said lug so that the rear receiver wall can be re-positioned to permit the bolt carrier assembly to be removed from the receiver.

Preferably there is provided a plurality of radial lugs for locking said bolt to the barrel, and a latch means biassed, shaped and dimensioned to interleave said lugs, said latch means being longitudinally retractable with respect to said housing means.

Preferably the latch means interleaves between only two adjacent lugs.

Conveniently, the housing means is a block, the bolt is mounted within a bore of said block and the latch means is slidably mounted in a blind groove provided in an outer surface of the block. Preferably, the outer surface of the block is situated adjacent a member arranged to carry a main drive spring.

Preferably the latch means comprises a bar member shaped and dimensioned to engage between adjacent lugs and a compression spring, which may be a coil spring, which are both arranged in the blind groove with the spring between the bar member and the blind groove closure.

Advantageously the bar member has a transverse slot and a transverse pin is arranged in the block to cooperate with said transverse slot to thereby limit the extent of longitudinal travel of the bar member.

The terms "forward" and "rearward" and similar adverbially phrases used herein are used in relation to the gun muzzle so that, for example, the buttstock is positioned rearwardly of the muzzle.

The invention will now be described by way of example with reference to the accompanying drawings, in which,

• Figure 1 shows a left hand side view of a gas operated fully automatic gun in accordance with this invention, drawn to a reduced scale in comparison with the remaining figures,
• Figure 2 shows a partial, longitudinal, cross-sectional, right hand side view of the gun shown in Figure 1 with the gun cocked and ready to fire,
• Figure 3 shows a partial longitudinal, cross-sectional, right hand side view of the gun shown in Figures 1 and 2 but with the trigger squeezed and the bolt in the firing position,
• Figure 4 shows a partial longitudinal, cross-sectional, right hand side view of the gun shown in the preceding Figures but with the trigger squeezed and the bolt in its most rearward position thereby permitting a further cartridge to feed,
• Figures 5A, 5B, and 5C show pictorial views of the parts of the bolt carrier assembly which are welded together with Figure 5A being an exploded view and Figures 5B and 5C showing opposing sides of the assembly,
• Figure 6A shows the bolt carrier assembly with the introduction of a pair of sear lugs,
• Figure 6B is a cross-sectional view on double arrow headed line B-B of Figure 6A showing an anti-bounce weight,
• Figure 6C is a cross-sectional view on double arrow headed line C-C of Figure 3A drawn to a larger scale,
• Figure 7A shows the complete bolt carrier assembly in accordance with the first feature of the invention,
• Figure 7B is a cross-section on double arrow headed line B-B of Figure 7A drawn to a larger scale,
• Figure 7C is a cross-section on double arrow headed line C-C of Figure 7A drawn to a larger scale,
• Figure 7D is a cross-section on double arrow headed line D-D of Figure 7B drawn to the same scale as Figure 7A,
• Figure 7E shows in partial cross-section a first angle projection of the bolt carrier assembly shown in Figure 7A,
• Figure 7F is a partial view in the direction of arrow headed line F in Figure 7A,

In the Figures like reference numerals denote like parts.

The gas operated automatic gun shown in Figure 1 has a receiver 1 to the rear wall channel 131 of which is connected a buttstock 2 and at the opposite end of the receiver 1 from the buttstock 2 there is connected a barrel 10. A pistol grip 11 is connected by a screw and nut underneath the receiver 1 and a fore grip 12 is connected by screws on the underside of the barrel 10. The pistol grip 11 is connected to the receiver 1 through the intermediary of a trigger guard 72 shrouding a trigger assembly 73 having a rotatable sear actuator (safety catch) 77.

Mounted in the bottom well of the receiver 1 is a cartridge magazine 4 which is of the drum type although it may be a flat box-type magazine. The magazine 4 is held to the receiver by a magazine latch assembly 5 having a spring arm 500 which is provided with a 90 degree twist 501 and pins 502, 503 which extend through the side wall of the receiver to engage cooperating holes in the magazine 4. The pins 502, 503 prevent fore and aft rocking of the magazine and to prevent lateral rocking of the magazine (with respect to the longitudinal axis of the gun) the magazine is provided with a vertical key 410 mounted within a "C" cross-sectionally shaped bulk-head 510 which is formed as a vertical front part of the trigger guard 72.

The spring arm 500 is arranged to be pushed outwardly, away, from the receiver by force being applied to the right end (looking forwardly) of an actuator rod 505 which passes through both side walls of the receiver 1 so that the pins 502, 503 disengage from the magazine 4.

A cocking handle assembly 6 is mounted on the left hand side of the receiver 1 incorporating a cocking bar sub-assembly 60 including a cocking bar 600 to which is connected a rotatable cocking handle 601. The cocking bar 600 is guided by a "C" cross-sectionally shaped sheet member 602 which has opposing open faces of the "C" welded to the receiver and which has an upper portion of the "C" removed to form a U-shaped, in cross-section, leg 603 that acts as a rail for the cocking bar 600. The cocking handle 601 is provided with a locking pin 604 which cooperates with a slot (not shown) in the leg 603 to selectively prevent longitudinal movement of the cocking bar and cocking handle.

Mounted on the top rear of the receiver 1 is a rear sight mount 96 and on the right hand side of the receiver is a carrying handle 97. Also on the right hand side of the receiver is an ejector slot 104 and in both sides at the front of the receiver are provided four cooling apertures 105 to assist in removing heat from the rear end of the barrel 10. A gas system 9 is connected in between the front of the receiver 1 and a foresight assembly 95. A bayonet lug attachment 98 is provided on the barrel and at the muzzle there is a flash suppressor 99.

Turning now to Figures 2, 3 and 4, the trigger assembly 73 has an arcuate finger pull trigger 730 pivotally mounted on a rod 731, the trigger 730 being biassed by a spring 732 acting in a blind note 736 within the trigger 730 with one end of the spring 732 against the closure of the blind hole 736 and the other end of the spring against a trigger spring retainer 733 which is stationary with respect to the receiver. The retainer 733 is located in a guide slot 734 in the trigger. A top rear face 735 of the trigger 730 acts against the conventionally supplied sear assembly 7 through the intermediary of a sear actuator 77. The sear actuator 77 has a hollow cylinder 770 which extends between the major walls of the receiver and slidingly mounted across the axis of the cylinder is an actuator 771 which is spring biassed toward the trigger top rear face 735. The sear assembly 7 has a sear 700 pivotally mounted on a transverse rod 701 which passes through the side limits of a U-shaped sear buffer 705 into opposing side walls of the receiver. Toward the bottom of the U shaped sear buffer 705, i.e. rearward of the gun, is a cross rod 706 which secures the buffer to the receiver and the buffer 705 is also located by a circularly cross-sectioned cross bar 504 which secures one end of the spring arm 500 and assists in holding the buffer 705 downwardly. The sear 700 is biassed into a non-firing position by a compression spring 702 located between a recess 703 in the sear 700 and a stud 704 mounted on the base of the receiver.

A bolt carrier assembly 3 is slidably mounted upon a rail 101 in the receiver and the bolt carrier assembly comprises a block 300 which is suitably shaped to contact with the rail 101 and in which is secured a pair of vertical (as shown in Figures 2, 3 and 4) sear locking lugs 325, one on each side of the gun longitudinal axis (only one of which is shown in the sectional view of Figures 2, 3, and 4). Secured, for example, by welding to the top of the block 300 is a "P" cross-sectionally shaped sheet member 301 with the upright of the "P" being horizontally disposed so the "P", as it were, lies on its back. Inside the wrapped over, enclosed portion of the "P" is a spring biassed antibounce weight (not shown) and longitudinally disposed adjacent to the non-enclosed portion of the "P" is a main drive spring assembly 302. For ease of explanation, it should here be stated that the main drive spring assembly 302 has been shown as if it were on the axial centre line of the gun but in practice the assembly 302 is offset to the right of the centre line when viewed forwardly so it does not interfere with the gas piston (hereinafter described). The main drive spring assembly 302 has a guide rod 303 of circular cross-section having end portions 304, 305 respectively, the part between the end portions 304, 305 being provided with parallel flats 306. Mounted over the guide rod 303 is a main drive spring 307. At the end of the P shaped member 301 remote from the block 300 is a bush 308 having a recess 309 into which the spring 307 is located and a circular cross-sectioned recess 310 to slidingly accept the end 304 of the guide rod 303. At the remote end of the main drive spring 307 from the bush 308 is a collar 311 which is secured to the guide rod 303 by a cross pin 312; the purpose of the collar 311 being to provide an end retainer for the spring 307 and to support the rear end of the guide rod 303 on a lug 102 on a receiver rear wall 100 which is mounted in the channel 131. The cross pin 312 extends through a slot in the side wall of the receiver and hence prevents the rear wall 100, which is slidably mounted, from dropping unless the collar 311 is removed from the lug 102 by sliding the cross pin 312 forwardly.

Mounted on the longitudinal axis of the barrel and inside the block 300 is a firing pin 313 which is biassed in a rearward position by a compression spring 314 with the limits of travel of the firing pin being maintained by a slot 315 in the firing pin cooperating with a cross pin 316, the spring 314 and pin 316 being provided essentially for a removal of the firing pin.

Encompassing the front portion of the firing pin is a bolt 317 which is slidingly rotatable on the longitudinal axis of the barrel inside the block 300 and is thus movable relative to the carrier assembly. The bolt 317 is conventionally provided with a cam pin 318 which pin 318 cooperates in known manner with a cam slot (not shown) in the left hand side (looking forwardly) of the block 300. Further, the bolt 317 is provided in conventional manner with an ejector pin 319 which is offset to the left (looking forwardly) of the barrel longitudinal axis and which pin is forwardly biassed by a coil spring 320, the forward extent of travel of the pin 319 being limited by a stop 321 acting in a slot in the pin 319. The bolt 317 also has a spring biassed claw (not shown since it is positioned on the right of the longitudinal centre line looking forwardly) which in operation engages the cannelore of a cartridge for removal of the cartridge from a chamber 109 that is situated in a barrel extension 110. At the rearward end of the barrel extension 110 are locking lugs 111 with which corresponding lugs 322 on the bolt 317 interleave and when the bolt is rotated by the action of the cam pin 318 in its cooperating cam slot locks the bolt lugs 322 into engagement with the lugs 111 so that the bolt 317 is unable to m6ve in a rearwards direction. So as to ensure that the lugs 322 of the bolt correctly interleave with the lugs 111, the bolt when withdrawn from the barrel extension 110 is prevented from rotating by a latch 326 which is generally of V-shaped cross-section and is forwardly biassed by a spring 327 to engage between two of the top-most lugs 322. The latch and spring 327 are on the longitudinal axis of the gun and movable within the block 300 by an amount determined (in the ultimate) by a slot 328 in the latch 326 and a transverse stop pin pin 329.

A feed ramp 114 is provided on the lower internal periphery of the barrel extension to facilitate entry of a cartridge into the chamber 109. The barrel extension 110 which is secured to the barrel 10 by an external screw thread 112 on the barrel is connected to the receiver 1 by a block 113.

Located at a predetermined distance along the barrel 10 is the gas system 9 having a rearwardly inclined gas port 900 which is connected to a gas cylinder 901 in which operates a piston 902. The gas cylinder 901 is mounted between the conventional foresight assembly 95 and a bush 904 which is arranged to align the gas cylinder 901 with the receiver 1. A compression spring 903 biasses the piston 902 in a forwards direction toward the foresight assembly 95. It will be seen that the guide rod 303 is extended forwardly of the barrel extension so that the end 304 is adjacent the bush 904. When the bolt carrier assembly is in its extreme forward position the piston 902 is arranged to substantially abut the forward end bush 308 of'the "P" shaped member 301.

In operation, to cock the gun, the cocking handle 601 is rotated anticlockwise as viewed in Figure 1 to release the locking pin 604 and the handle 601 pulled rearwardly which in turn pulls the bolt carrier assembly 3 rearwardly so that it is held by the sear 700 engaging lugs 325; the various elements adopting the positions shown in Figure 2. The cocking handle 601 is then returned to its original position and the locking pin 604 rests in its associated recess to prevent unwanted movement of the cocking handle assembly 6.

To fire the gun, the trigger 730 is pulled rearwards, as shown in Figures 3 and 4, against the force of spring 732 so that the face 735 rotates clockwise about rod 731 and as a consequence face 735 pushes actuator 771 upwardly so as to tilt the sear 700 anticlockwise, as viewed in Figures 2, 3, 4, against the compressive force of spring 703. As the sear 700 tilts it releases the lugs 325 thereby releasing the bolt carrier assembly 3 which is driven forwardly by the tension created in cocking the main drive spring 307. As the bolt carrier assembly 3 moves forward toward the barrel extension 110 the lower edge of the bolt strips a cartridge 499 from the magazine 4 and continued travel of the bolt carrier assembly causes the cartridge 499 to ride over the feed ramp 114 in the barrel extension to thereby insert the cartridge into the chamber 109. However, as the bolt lugs 322 interleave the barrel extension lugs 111 the latch 326 which normally engages the lugs 322 of the bolt to prevent rotation thereof is pushed rearwardly against spring 327 by a member 130 so as to release the bolt and thus enable the bolt to rotate by the motion of the cam pin 318 along the cam slot. Rotation of the bolt 317, causes the lugs 322 on the bolt to rotate and engage, i.e. lock, with the lugs 111 of the barrel extension 110 thus locking the bolt 317 against rearward travel. The cartridge 499 is thus locked into the chamber 109 and the ejector pin 319 is pushed rearwardly so that the parts are in the position shown in Figure 3. Continued forward motion of the bolt carrier assembly 3 drives the firing pin 313 into the rear of the cartridge thereby igniting the cartridge charge. The bush 308 of the "P" shaped member 301 is then in substantially the same plane as the front part of end portion 304.

As the cartridge fires, it produces gas pressure and when the bullet passes the gas port 900 so the gas under pressure enters port 900 to expand in the cylinder 901. Pressure in the cylinder 901 causes the piston 902 to be driven rearwardly and because the piston 902 is arranged to normally abut the bush 308 on the guide rod 303 (although in practice there will be a small gap between the adjacent faces owing to tolerances) so the bush 308 is driven rearwardly to compress the main drive spring 307. It is to be noted that, as shown in Figure 4, the length of travel of the piston 902 is much less than. that of the bolt carrier assembly 3, the piston stopping against a shoulder but the bolt carrier assembly continuing rearwardly due to the energy and impulse stored within its mass during acceleration by the gas system. Because the gas pressure in the barrel ceases as soon as the bullet leaves the barrel, the position and amount of gas permitted to enter the gas cylinder 901 is carefully arranged. The rearward motion of the bolt carrier assembly 3 and hence cam slot causes the cam pin 318 to retraverse the cam slot and thereby rotate and unlock the bolt 322 from the barrel extension lugs 111. Continued rearward motion of the bolt carrier retracts the bolt 317 and causes the cartridge extraction claw (not shown) carried by the bolt, which when in the locked position engaged the cannelore of the cartridge, to pull rearwardly on the cartridge and to thus remove the cartridge from the chamber 109. Further rearward motion of the bolt carrier assembly 3 causes the spent cartridge to align with the ejector slot 104 in the right hand side of the receiver. The ejector pin 319, due to its. offset on the left side of the longitudinal axis of the spent cartridge and the claw on the bolt holding the right side of the cartridge, combined with the spring tension of spring 320 pushing the pin 319 forwardly causes the cartridge to be ejected out of the ejector slot 104. Continued rearward motion of the bolt carrier assembly uncovers the top cartridge in the magazine and carries the lugs 325 beyond the rear of the sear 700 so as to thereby recock the gun and the parts pass through the position shown in Figure 4 with a fresh cartridge 499' having risen into the feed area 103. Provided the trigger 730 is still squeezed the bolt carrier returns forward and the cycle of events will repeat until such time as either the trigger is released so that the sear 700 re-engages the lugs 325 with the shock of the engagement being taken by the buffer 705 (as shown in Figure 2) or the final cartridge is fired when, if the trigger is still squeezed, will result in the bolt finishing the cycle of events locked to the barrel extension as shown in Figure 3.

It is to be noted that in the present invention the bolt carrier assembly 3 is retarded solely by the action of the main drive spring 307 and unlike known gas operated automatic guns, the present. invention does not have a bolt carrier assembly which impacts in any way against the rear receiver wall 100, i.e., the aforementioned buffer of the M16 and comparable weapons is not provided and with no buffer impact or direct impact the controllability of the gun is improved.

The bolt carrier assembly will now be described in greater detail.

Referring to Figures 5A, 5B and 5C the metal block 300 is seam welded to the P cross-sectionally shaped member 301 so that the block 300 underlies one end of the outer, longest, flat surface of the P shaped member. At the opposing end of the P cross-sectionally shaped member 301 from the block 300 is a bush 308 having a leg 332 which is shaped and arranged to fit within the wrapped over portion of the P shaped member 301 and the bush 308 is welded to the P shaped member 301.

The P cross-sectionally shaped member 301 is formed from a metal sheet and the wrapped over join of the enclosed part of the P is seam welded at locations 331. The P shaped member 301 has a slot 333 cut into the top of the P shape at the end of the member 301 adjacent to the bush 308. The slot 333 has an arcuate end and is dimensioned to act as a cocking handle shoulder 334 and it is with this shoulder that the cocking handle assembly cooperates to draw the member 301 rearwardly and thus cock the gun. It is to be noted that the length of the slot 333 is less than that of the leg 332 so that the interior of the wrapped over portion of the P shaped member 301 is closed at its end adjacent the bush 308.

It is to be noted that the face of the bush 308 remote from the P shaped member 301 is the surface upon which the gas piston 902 strikes. The bush 308 has the recess 309 to accept one end of the main drive spring 307 and the circularly cross-sectioned recess 310 to accept the end 304 of the guide rod 303. In the left hand side (as shown in Figures 5A and 5B) of the bush 308 is a slot 335 to facilitate mounting the main drive spring assembly 302 (see also Figure 7E). In this respect, the width of the slot 335 is only slightly greater than the width between the flats 306 on the guide rod 303 so that the guide rod 303 can be inserted into the bush 308 and the main drive spring 307 holds the circular end 304 of the guide rod in the recess 310. The slot 335 is thus too small to permit the drive spring 307 to pass therethrough. On the opposite side of the bush 308 to the slot 335 is a groove 336 which aligns with the slot 333 in the P shaped member 301.

The block 300 has two parallel bearing surfaces 338 upon which the bolt carrier assembly 3 runs on guide rails 101, and an extended portion 339 having the same depth as the sear locking lugs 325. The purpose of the extended portion 339 is to ensure that a cartridge is held downwardly in the magazine when the bolt carrier assembly 3 makes a rearward traverse thus ensuring that the locking lugs 332 on the bolt do not strike the shoulder of the cartridge and thereby damage the cartridge. As best shown in Figure 7C, the block 300 has a longitudinal bore 340 within which slides the bolt 317 and the bore 340 is linked via a passage 341 to a further bore 342 which is coaxial with the bore 340 and which houses the spring 314 for the firing pin 313.

In the right hand side (as viewed in Figures 5A and 5B) of the block 300 is the cam 343 within which the cam pin 318 operates. A transverse hole 344 is provided through the block 300 for the cross pin 316.

In the top of the block 300, i.e. in the surface adjacent the P shaped member 301 is a blind longitudinal groove 345 in which the bolt latch 326 is subsequently positioned and a transverse groove 346 is provided for positioning the stop pin 329. The forward end of the block 300 has a transverse clearance hole 347 opposite the cam 343 dimensioned to permit a tool to be inserted thereinto so that pressure can be applied to the cam pin and thereby enable the cam pin to be removed.

Extending downwardly through the rear end of the P shaped member 301 and block 300 are a pair of holes 348 for the sear locking lugs 325.

Referring now to Figures 6A, 6B and 6C, the sear locking lugs 325 are seen to be of circular cross-section with the lower end of the lugs being provided with a forwardly facing flat surface 349 which cooperates with the rear top portion of the sear 700. By mounting the locking lugs 325 through both the P shaped member 301 and the block 300 improved strength is provided to the join between the member 301 and block 300. The locking lugs 325 are held in position by a cross pin 316 having a circular cross-section with a flat upper face 351 which is machined to form an abutment face 352. The pin 316 is contacted on its flat upper face 351 by an orthogonally extending pin 353, the pin 353 being provided to prevent total removal of the cross pin 316 by the pin 353 contacting abutment face 352 (as shown in broken lines in Figure 6C). As shown in Figures 2, 3,4 and in 7D, the cross pin 316 also maintains the longitudinal position of the firing pin 313. The reason for the cross pin 316 being permitted to be partially withdrawn is so that the firing pin 313 may be removed for disassembly of the cam pin and bolt from the bolt carrier. The purpose of the spring 314 associated with the firing pin is to ensure constant contact with the cross pin. It will be seen from Figures 7D and 7C that the firing pin is generally of circular cross-section with the rearward end of the firing pin having a rectangular cross-section and the slot 315 being provided in the upper edge to accommodate cross pin 316.

An anti-bounce weight in the form of a square cross-sectionally shaped rod 354 has a chamfer 355 at one end and a reduced circularly cross-sectioned end 356 at the other to accommodate a compression spring 357. The anti-bounce weight is thus positioned so that the chamfer 355 rests between the wrapped over part of the "P" and the locking lug 325 at one end, and is under tension by the compression spring 357 abutting leg 332. The function of the anti-bounce weight 354 occurs after the bolt 317 hits the barrel extension 110 and the cam pin 318 is rotated by the cam 343. The block 300 continues to travel forwardly to drive the firing pin 313 into the back of the cartridge and simultaneously to impact barrel extension. When the block 300 striked the barrel extension the block and the members secured to it tend to bounce rearwardly away from the barrel. The purpose of the anti-bounce weight is that, as the block 300 strikes the barrel extension and tries to rebound, the anti-bounce weight mass impetus carries it forwardly against the force of spring 357 until it impacts the leg 332 thereby substantially cancelling the rebound of the bolt carrier. In this manner, substantially zero restitution is provided. Once the shock impact has been overcome so the anti-bounce weight is driven rearwardly by the compression spring 357 and the chamfer 355 ensures that the anti-bounce weight 354 is nested between the "P" shaped member 301 and locking lug 325 and in this manner the anti-bounce weight 354 is wedged to prevent multiple bouncing back and forth within the bolt carrier.

Referring to Figure 7A, the cam pin 318 is shown at the bottom of the cam 343 and in such a position the lugs 322 of the bolt are arranged to interleave with the lugs 111 of the barrel extension and the lugs are locked in position by the latch 326. As previously described, the latch 326 has a slot 328 removed from its top surface (as viewed in Figures 2, 3, 4, 7A and 7D) and, as shown particularly in Figure 7D, the latch 326 is biassed forwardly by the spring 327. The stop pin 329, mounted in groove 346, in conjunction with slot 328 determines the limit of travel of the latch 326. As shown in Figure 7C, on opposing sides of the axis of the bolt 317 is the ejector pin 319 and the extractor claw 360. The pin 319, which is housed within the wall of the bolt, has been described above and so will not be described in any further detail.

The extractor claw 360 forms part of the peripheral wall of the bolt. The claw has an opening 361 for permitting the rim of the cartridge to enter thereinto and is pivoted about an axle 362 by a compression coil spring 363 so that the opening 361 is biassed toward the axis of the bolt 317.

As mentioned above, the main drive spring 307 is located at one end in recess 309 and at the other end it is held by the collar 311. The collar 311 has the cross pin 312 guided by a slot 364 and the free end of the cross pin 312 lying outside the collar 311 is connected to a handle 365. The collar 311 is arranged such that, when forced rearwardly by the main drive spring 307 so the collar, which is tubular, is located on the lug 102 on the rear receiver wall 100. A slot is provided in the right hand side receiver wall, looking forwardly, to permit the cross pin 312 to pass therethrough so that the handle 365 is on the outside of the receiver. To permit disassembly of the bolt carrier assembly 3 the buttstock 2 is removed and the rear receiver wall 100 is arranged to be vertically slidable. So as to permit the wall 100 to slide, the handle 365 is pushed forwardly (within the confines of the slot 364) so that the collar 311 disengages the lug 102. The wall 100 is thus able to move downwardly and the bolt carrier'assembly may be slid rearwardly along rail 101 and removed from the receiver 1.

In operation, as the bolt carrier assembly 3 lugs 322 interleave the lugs 111 on the barrel extension so the member 130 pushes the latch 326 rearwardly against the compressive force of spring 327. The bolt is thus unlatched and free to rotate and as the bolt carrier assembly 3 continues its forward motion so the bolt chambers the cartridge and continued forward movement of the block 300 causes the cam pin 318 to be driven up (as viewed in Figure 7A) the cam 343 thereby rotating the bolt and locking the bolt to the barrel extension. The impact of the block 300 against the barrel extension causes the anti-bounce weight 354 to be driven forwardly against the force of spring 357 and, due to the careful calculation of the weight of the bar 354, so the tendency for the block 300 to bounce is substantially eliminated.

The bolt carrier assembly of this feature of the invention has the following advantages:-1. high column strength is provided by virtue of the P shaped cross-section of member 301,

• 2. a tunnel within the wrapped over portion of the "P" is provided for the anti-bounce weight 354,
• 3. the arrangement of the main drive spring 307 lying alongside the wrapped over portion of the "P" and adjacent the planar surface facilitates the maximum diameter to be given to the main drive spring since it is not necessary for it to be bounded on all sides by a sheathing,
• 4. the planar back face of the P shaped member 301 masks the spring from barrel heat,
• 5. by arranging for the sear studs to traverse the P shaped member 301 and the block 300, increased strength and rigidity is provided.

Attention is directed toward our co-pending European Patent applications Nos. 0125705 published 21·11·84, 0127193 published 05.12.84, 0127194 published 05.12.84 and 0132560 published 13.02.85, which relate to various other features of the gun described above.