Sear buffer for a gas operated gun & gun embodying same

This invention relates to a sear buffer for a gas operated gun which may be automatic or semi-automatic and to a gun embodying the sear buffer.

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 principally to the latter form of operation.

Automatic and semi-automatic guns are well discussed in literature and examples are "Smal 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 of 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 ARl8 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 hanger 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 dirven all the way forward by the drive spring. So as to cushion the impact of the bolt/bolt carrier assembly against the sear it is desirable to provide a shock absorbing buffer for the sear.

A principal object of this invention is to provide a sear buffer of simple construction.

According to one aspect of this invention there is provided a sear buffer for a gas operated gun including a U-shaped member with bowed longitudinal arms, the free ends of the arms being arranged for mounting a sear, and locating means for securing said U-shaped member to the gun whereby the arms act as an extension spring and the bow in the arms is arranged to be temporarily reduced when the sear is contacted by a reciprocating bolt means.

According to a further aspect of this invention there is provided a gas operated gun having a receiver within which reciprocates a bolt means arranged to be actuated by a pivotable sear and a sear buffer, said sear buffer including a U-shaped member with bowed longitudinal arms, the free ends of which are secured to the pivotal sear, and locating means securing the sear buffer to the receiver whereby the arms act as an extension spring and the bow in the arms is temporarily reduced when the sear is contacted by the bolt means.

Conveniently the sear is located between the free ends of the bowed arms.

Preferably the arms are bowed inwardly of one another and the free end of the arms has a foot arranged with the heel portion of each foot abutting the receiver lower wall and the toe portion of each foot supporting the pivotal sear by a rod passing through the feet and sear.

Advantageously the locating means include block provided adjacent the base of the U-shaped member between said arms which block is secured to the receiver lower wall and laterally locates the U-shaped member. The receiver is advantageously formed from sheet material and in the region of the base of the U-shaped member preferably has each side wall formed from a treble material thickness. The locating means preferably further includes a rod passing through the arms of the U-shaped member adjacent the base thereof and also through the treble material thickness of each receiver side wall to thereby longitudinally locate said U-shaped member.

Advantageously the locating means includes a further rod passing transversely through the receiver side walls which abuts the top edge of the bowed arms and which, in conjunction with said heels locate the arms in a third, vertical, direction.

The terms "forward" and "rearward" and similar adverbial 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 2A shows a partial sectional plan view of the rear of the gun receiver demonstrating the sear buffer in accordance with this invention;
• Figure 2B is a cross-section along double arrow headed line B - B of Figure 2A.

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 II 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.

A cocking handle assembly 6 for a bolt carrier assembly 3 (shown in Figure 2B) is mounted on the left hand side of the receiver 1 incorporating a cocking bar sub-assembly 60 including a cocking handle 601.

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 nuzzle there is a flash suppressor 99.

Turning now to Figures 2A and 2B, 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 hole 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. 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 ccnpression spring 702 located between a recess 703 in the sear 700 and a stud 704 mounted on the base of the receiver.

The sear buffer 705 shown particularly in Figures 2A and 2B, is a U-shaped member having side limbs 707 with a rod 706 extending through the part of the limbs near the base of the U-shape and through three thicknesses of receiver wall. The buffer is thus supported in a longitudinal direction by the rod 706, and to support the buffer laterally a block 208 is provided between the limbs 707 which is secured to the receiver base. The limbs of the buffer are also located in a vertical direction, by the cross bar 504 of the magazine latch abutting the top of the limbs. The limbs 707 are inwardly bowed 708 with respect to one another so as to provide the limbs with resilience. The open ends 709 of limbs have feet comprising a heel which rests on the lower wall of the receiver and, a toe portion through which the transverse rod 701 extends to pivotally support the sear 700 between the feet.

The sear 700 has wings 710 which overlap the top of the limbs and rest on the limbs when the trigger is released. The sear also has a longitudinal groove 711 to permit a longitudinally extended portion 339 of the bolt carrier assembly block 300 to pass therethrough. - Mounted at the rear of the bolt carrier assembly 3 and transverse to the direction of reciprocation of the bolt carrier assembly are two sear locking lugs 325, which are arranged to cooperate with the rear of the sear, such that when the sear 700 is in the position shown in Figure 2B the bolt carrier assembly 3 is prevented from moving forwardly to a firing position.

When the forward lip 712 of the sear is rotated in a clockwise direction ( as viewed in Figure 2B) by the trigger assembly 73 the rear of the sear is removed from engagement with the lugs 325 and the main drive spring (not shown) drives the bolt carrier assembly 3 forwardly to the firing position. In the present gas operated gun the bolt carrier assembly 3 is driven rearwardly by the gas system 9 so that the lugs 325 are behind the rear of the sear 700. If the trigger is still pulled so that the sear is rotated out of the path of the sear lugs then the gun will continue on an automatic cycle. If, however, the trigger is released so that the sear returns to the position shown in Figure 2B then the sear lugs 325 will contact the rear of the sear and cause an extension of the limbs 707 of the sear buffer with the result that the bow in the limbs is slightly reduced, but because the limbs 707 are made of a material which has a degree of elasticity, for example, tampered steel, the normal bow in the limbs is returned after impact by the locking lugs 325, i.e. the limbs act as an extension spring.

The principle purpose of the buffer 705 is to reduce damage to the abutting surfaces and vulnerable adjacent edges of the sear and sear lugs caused by contact when the sear is only partially rotated toward the rest position shown in Figure 2B.

Attention is directed toward our co-pending Application Nos. which relate to various other features of the gun as herein described.