Firing Rate Regulator For A Gas-operated Firearm

Abstract

A firing rate regulator for an automatic firearm having a breech mechanism operated by gas pressure. A breech casing has a gas channel and a throttling element is responsive to a temperature change for regulating the gas pressure by varying the cross sectional area of gas flow through the gas channel. Members made of materials having different coefficients of thermal expansion move the throttling member. The throttling element may be a piston with an annular groove movable in the casing and biased on one side by a spring and on the other side by a liquid such as mercury whereby the position of a flank of the groove determines the cross sectional area of the gas channel or a rotatable pin projecting into the gas channel with a bimetal spring for rotating the pin to vary the cross sectional area of the gas channel.

Description

The invention relates to a firing rate regulator for a gas-operated firearm of the type comprising a throttling element which in response to temperature controls the gas pressure for operating a breech mechanism of the firearm by varying the cross sectional area of flow through a gas channel.

A known form of rate regulator of this type consists of a pin inside a cylinder. An annular cross section of flow for the gases remains between the pin and the cylinder. The pin as well as the cylinder are made of steel. When the weapon is fired the pin which is immersed in the flowing gas becomes hotter more quickly than the greater mass of the cylinder. The pin therefore initially expands more rapidly than the cylinder and the annular cross section of flow is reduced, throttling the passage of the gas. This effect compensates the tendency of the firearm to increase its firing rate.

This known type of firing rate regulator has the defect that in the course of a prolonged burst of firing the temperature difference between the pin and the cylinder gradually entirely vanishes and that the rate regulator then ceases to exercise any control.

It is the object of the present invention to eliminate this defect.

A firing rate regulator according to the invention for a gas-operated firearm comprises a throttling element which in response to a temperature change regulates the gas pressure for operating a breech mechanism of the firearm by varying the cross sectional area of flow through a gas channel, and means for moving the throttling element comprising members made of materials having different coefficients of thermal expansion.

The invention is illustrated by way of example in the drawings of which:

FIG. 1 is a section of the barrel of a firearm having a firing rate regulator according to the invention;

FIG. 1a is an enlarged representation of part of FIG. 1;

FIGS. 2 to 5 are sections taken on the lines II--II, III--III, IV--IV and V--V of FIG. 1a;

FIG. 6 is a sectional view of an alternative part of FIG. 1 for use in the regulator of FIGS. 1 to 5;

FIG. 7 is a section of an alternative embodiment of a firing rate regulator according to the invention;

FIG. 8 is a view in the direction of the arrow A in FIG. 7;

FIG. 9 is a view in the direction of the arrow B in FIG. 8;

FIG. 10 is a section of a further embodiment of a firing rate regulator according to the invention and

FIG. 11 is a view similar to that of FIG. 9 of the regulator of FIG. 10.

With reference to FIGS. 1 and 1a the barrel 1 of an automatic firearm is held fast in a breech casing 2. The breech casing 2 includes a cylindrical chamber 3 in communication with the interior of the barrel 1 through a gas passage 4. The chamber 3 is closed by a plug 5, and contains a slidably movable piston 6 attached to a piston rod 7. The rear end of the piston rod 7 projects through the rear end of the chamber 3 and abuts onto a sleeve 8 which is biased by a spring 9. In the illustrated position of the piston 6, the head of the piston bears against an end face 10 of the plug 5. The chamber 3 also contains a stack of annular springs 11 which form a buffer for the piston 6 by cooperating with an annular face 12 on the back of the piston head. A bore 13 in the wall of the chamber 3 connects the chamber interior with the ambient atmosphere.

The bore of the chamber 3 at its forward end 14 has a larger diameter than its rear part 15. The two diameters 14 and 15 are separated by a shoulder 16. The diameter of a rear portion 17 of the plug 5 equals that of the chamber bore 15 into which it projects. The diameter of a front portion 18 equals the diameter of the chamber bore 14. An annular shoulder 19 separates the portions 17, 18 of the plug 5. An annular chamber 20 is formed between the shoulders 16 and 19. Adjacent to the annular chamber 20 the rear portion of the plug is provided on its circumference with an annular groove 21. A second annular groove 76 is machined into the rear portion of the plug 5. The gas passage 4 communicates with the annular groove 76. The two annular grooves 21, 76 communicate through a helical groove 75 cut into the circumferential surface of the rear portion of the plug 5. The front annular groove 21 communicates through four radial ducts 22 (FIG. 2) with a blind axial bore 23 in the plug 5. The bore 23 is open at the end face 10 of the plug and is coaxial with the axis of the cylindrical chamber 3.

The plug 5 projects from the forward end 14 of the chamber 3 where it is formed with a flange 24 which abuts a face 25 of a shoulder at the front end of the chamber 3. A blind bore 26 is drilled through the plug 5 from its front end axially aligned with the axis of the chamber 3. Two grooves 27 and 28 which extend around the entire internal circumference of the bore 26 are machined into its internal wall. Milled at equidistant intervals into the circumferential surface (FIG. 3) of portion 18 of the plug 5 are four grooves 29 which communicate with the annular chamber 20 and which are axially parallel to the chamber axis. Four radial bores 30 connect the grooves 29 to the groove 28. A number of ducts 31 extend from the groove 27 to an annular face 32 of the flange 24 of the plug 5. A cylindrical container 33 is inserted into the bore 26 of the plug 5 and threadedly located therein. The rear portion of the container 33 has a central bore 34. A groove 35 machined into the wall of the bore 34 contains an O-ring 36. The container 33 encloses a cavity 38 which is completely filled with mercury. Mercury has a much higher coefficient of thermal expansion than the steel of which the container 33 and the plug 5 are made. A plunger 37 is movable inside the bore 34 and projects into the container 33. A stack of Belleville springs 39 bears against a rear face 47 of the bore 26 of the plug 5. The bore 26 contains a piston 40 whose position is controlled by the Belleville springs 39, and by the plunger 37 which projects from a rear face 42 of the container 33. End faces 44 of the piston 40 each contain two intersecting diametrical grooves 43 which are perpendicular to each other. The grooves 43 are shorter than the diameter of the piston 40 and longer than the diameter of the plunger 37. The grooves 43 in both end faces 41 are interconnected by a central bore 44. Machined into the piston 40 is an annular groove 45 which is sufficiently wide for its rear flank 46 to come below the groove 28 when the piston 40 is displaced, and thus to establish communication between the groove 28 and the groove 27. The described rate regulator functions as follows:

Before firing begins, when the firearm to still cold, the piston 40 completely covers the groove 28 in the plug 5 as shown in FIG. 1a. Moreover, the groove 45 in the piston 40 is located so as to be in communication with the groove 27 in the plug 5. In the course of firing a round (not shown) powder gases pass from the barrel into the gas passage 4. The powder gases will pass through this passage and enter the rear annular groove 76, thence flowing along the helical groove 75 into the front annular groove 21 and into the annular chamber 20. From here the gas flows through ducts 22 and 23 to the face of the piston 6 and its pressure accelerates the piston and piston rod to the rear thus operating the breech mechanism of the automatic firearm in a known manner. The front end of the piston 6 when it reaches the end of its stroke, will have uncovered the bore 13 permitting the gas to escape from the chamber 3 to atmosphere. The annular face 12 of the piston strikes the stack of springs 11 which decelerate the piston and cause it to rebound towards the plug 5 with which it remains in contact until the next round is fired.

As the gun continues to fire the barrel 1 is heated up by the powder gases, and this heat is transmitted through the chamber 3 to the plug 5 enclosing the container 33 and to the mercury confined in the cavity 38 and all these parts 3, 5, 33, 38 therefore likewise become hot. This rise in temperature causes the mercury to expand more than the container 33 and the plug 5. Expansion of the mercury displaces the plunger 37 and the piston 40 to a distance dependent on the temperature of the barrel, against the resistance of the Belleville springs 39. The rear flank 46 of the annular groove 45 of the piston 40 is thus displaced rearwards so as to be in communication with the groove 28 of the plug 5. A proportion of the gas diverted from the barrel 1 through the gas passage 4 after the firing of each round will therefore now escape from the annular chamber 20 through the grooves 29 and the bores 30 into the groove 28 and from there into the groove 45, the groove 27 and via the ducts 31 to atmosphere. Consequently less gas pressure is available for displacing the piston 6 which is less powerfully accelerated and therefore delays the unlocking of the breech mechanism, (not shown) until the gas pressure in the barrel 1 has fallen to a lower level. The lower residual gas pressure transmits less power to the breech mechanism which therefore moves more slowly and reduces the firing rate which had increased by virtue of the firearm having become hotter.

During the displacement of the piston 40 the pressures equalize through the bore 44 and the grooves 43 in the piston 40 between the rear end and the chamber in front of piston 40 defined by its end face 41 and the end face 42 of the container 43. When after the termination of firing the plug 5 and the container 33 cool off the plunger 37 and the piston 40 are restored to their initial position by the thrust of the Belleville springs 39. The biasing force of the springs 39 is sufficient to ensure that the frictional resistance to motion affecting the plunger 37 and the piston 40 due to carbon deposits on the wall of the bore 26 or due to the sealing ring 36 are overcome.

During the period before the above-described thermal gas regulation has not yet become effective, an increase in the firing rate is resisted due to the design of the gas channels in the rear portion 15 of the plug 5. The gas channels comprising the passage 4, the annular grooves 21, 76, the helical groove 75 and the bores 22, 23 cause a drop in pressure of the gases passing through them. This pressure drop is due to a lowering in pressure incurred in the gas channels by friction and turbulence of the gas. These pressure losses are accentuated by the length of the gas channel and by angles in its path, and they become more pronounced as the gas temperature and consequently the gas velocity rises so that the design of the entire system of channels already operates to resist a rise in the firing rate.

FIG. 6 illustrates an alternative form of container for use with the described regulator. As shown in FIG. 6 the bore 26 of the plug 5 contains a flexible resilient corrugated tube 49 which is closed at one end by a cover 50 that screws into the plug 5 and at the other end by a base 51 abutting against the piston 40. The rate regulator functions substantially in the same way as that described with reference to the first embodiment. The mercury enclosed in the container 48 expands at a higher rate than the plug 5 when both become hot and therefore displaces the piston 40 to the rear. The corrugated tube 49 is elastically elongated by the thrust of the mercury on the base 51.

With reference to FIGS. 7 to 9 the barrel 1 is attached to a breech casing 52 which contains a forwardly open cylinder 53. A sleeve-shaped extension 55 of an insert 54 projects into the open end cylinder 53 and is threadedly connected thereto. The cylinder 53 and the extension 55 together define a cylindrical chamber 56 in which a piston 57 is slidably movable. In its position of rest the piston 57 is biased by a spring 59 acting on its piston rod 58 against a bottom 60 of the bore of the extension 55. A gas passage 61 passing from the interior of the barrel 1 communicates with a bore 62 in the insertion 54. The bore 62 is connected to a blind bore 63 which is coaxial with the sleeve shaped extension 55 and communicates with the interior of the cylinder chamber 56. The bore 62 ends at the upper face 65 of the insertion 54. The part of the bore 62 between the junction of the blind bore 63 and the bore 62 and the upper face 65 of the insertion 54 forms a venting channel 64. A bore 66 penetrates the insertion 54, its axis perpendicularly intersecting the axis of the venting channel 64. This bore 66 has a larger diameter than the venting channel 64. A pin 67 is rotatably mounted in the bore 66. Machined into the ends of the pin 67 which project from both sides of the insertion 54 are grooves 68 which have coincident axes of symmetry and contain the axis of the pin 67. The pin 67 contains a slot 69 of a width equal to the diameter of the bore 64 and bounded by an edge 73. The plan of symmetry of the slot 69 is normal to the axis of the venting channel 64 and also contains the axis of the bore 66. Attached to each side of the insertion 54 are holders 70. Each holder 70 grips the ends of two metal strips 71a, 71b having different coefficients of thermal expansion of a bimetal spring 71. The other ends of the metal strips 71a, 71b of the bimetal spring 71 are riveted together at 72 and project into the slots 68 of the pin 67. Rivets 72 having round heads contact the walls of the slots 68 at points which are coplanar. This plane is normal to the plane of symmetry of the slot 68 and is offset from the axis of rotation of the pin 67.

This embodiment described above functions as follows. In the position of rest of the pin 67 which is shown in FIG. 7 the venting channel 64 is closed. The insertion 54 is heated by the gas diverted from the barrel during firing through the bores 61, 62, 63 to the piston 57 as well as by thermal conduction and radiation from the barrel 1. The temperature of the two bimetal springs 71 is raised by heat radiated through the insertion 54 and through the barrel 1. Owing to the different coefficient of thermal expansion of the metals of the strips 71a, 71b of the bimetal springs 71 the latter flex and their ends apply a clockwise torque to the pin 67 (as viewed in FIG. 9). Rotation of the pin 67 brings the edge 73 bounding the slot 69 in the pin 67 into the venting channel 64, thereby permitting some of the gas entering through the channel 62 to escape through the venting channel 64, the slot 69 in the pin 67 and the upper part of the venting channel 64. Consequently less gas will flow to the piston 57 and the firing rate of the firearm will slow down in the same way as described in connection with the first embodiment.

FIGS. 10 and 11 illustrate a further embodiment which merely differs from the embodiment of FIGS. 7 to 9 in that the gas channel 61, 62, 63 does not communicate with the ambient atmosphere. The bore 62 in this arrangement merely extends as far as the blind bore 63. The pin 67 crosses the bore 62, and the holders 70 for the bimetal springs 71 are attached to the upper end of the insertion 54. The pin 67 contains a bore 74 which in the position of rest shown in FIG. 10 is coaxially aligned with the bore 62 and which has the same diameter as the latter. Owing to the rotation of the pin 67 when the bimetal springs 71 become hot, the cross section of flow of the bore 62 is reduced and the gas supply to the piston 57 is throttled with a consequent reduction in the firing rate of the gun.

In the two embodiments illustrated in FIGS. 7 to 11 the pin 67 is rotated back into its former position when the gun cools by virtue of the bimetal springs 71 likewise becoming cooler.

Claims

I claim:

1. A firing rate regulator for an automatic firearm having a breech mechanism operated by gas pressure comprising a breech casing having a gas channel, a throttling element in said casing responsive to a temperature change for regulating said gas pressure by varying the cross sectional area of gas flow through said gas channel, said casing having a bore, said throttling element comprising a piston having an annular groove movable in said bore, a spring biassing said piston on one side and a liquid on the other side, whereby the position of a flank of said groove determines the cross sectional area of said gas channel, said casing and said liquid having different coefficients of thermal expansion.

2. A firing rate regulator for an automatic firearm having a breech mechanism operated by gas pressure comprising a breech casing having a gas channel, a throttling element in said casing responsive to a temperature change for regulating said gas pressure by varying the cross sectional area of gas flow through said gas channel, said throttling element comprising a rotatable pin projecting into said gas channel, and a bimetallic spring for rotating said pin to vary the cross sectional area of said gas channel.

3. A firing rate regulator according the claim 1, in which said liquid is mercury.

4. A firing rate regulator according to claim 1, wherein said casing has a port venting to the atmosphere and the position of said flank determines the cross sectional area of flow between a part of said gas channel and said port.

5. A firing rate regulator according to claim 2, in which said pin projects into a venting channel which connects said gas channel to atmosphere and a rise in temperature actuates said pin to be moved to increase the cross sectional area of said venting channel.