US3613500A

US3613500A - Combination projectile guide and firing chamber seal

Info

Publication number: US3613500A
Application number: US800103A
Authority: US
Inventors: Francis J Warin
Original assignee: TRW Inc
Current assignee: Northrop Grumman Space and Mission Systems Corp
Priority date: 1969-02-18
Filing date: 1969-02-18
Publication date: 1971-10-19
Anticipated expiration: 1988-10-19

Abstract

A firing chamber front end seal having two concentric tubular members with out-turned flanges at their leading ends. The flanges are adapted to be seated in a counterbore in the end of the weapon barrel. The inner diameter of the inner member is equal to the diameter of the barrel bore and concentric therewith. The inner member has a substantial wall thickness and strength with an internally frustoconically outwardly tapered end opposite the flanged end. The inner member is effective to act as a projectile guide to align a moving projectile with the weapon barrel. The outer member has a wall thickness less than the inner member and the end remote from the flanged end is adapted to be expanded by pressure of the propellant gases into sealing engagement with the inner diameter of the firing chamber thereby preventing gases from escaping from the chamber at the interface of the chamber and barrel.

Description

United States Patent Francis J. Warin Oakharbor, Ohio 800,103

Feb. 18, 1969 Oct. 19, 1971 TRW Inc. Cleveland, Ohio Inventor Appl. No. Filed Patented Assignee Great Britain 42/27 ABSTRACT: A firing chamber front end seal having two concentric tubular members with out-turned flanges at their leading ends. The flanges are adapted to be seated in a counterbore in the end of the weapon barrel. The inner diameter of the inner member is equal to the diameter of the barrel bore and concentric therewith. The inner member has a substantial wall thickness and strength with an internally frustoconically outwardly tapered end opposite the flanged end. The inner member is effective to act as a projectile guide to align a moving projectile with the weapon barrel. The outer member has a wall thickness less than the inner member and the end remote from the flanged end is adapted to be expanded by pressure of the propellant gases into sealing engagement with the inner diameter of the firing chamber thereby preventing gases from escaping from the chamber at the interface of the chamber and barrel.

COMBINATION PROJECTILE GUIDE AND FIRING CHAMBER SEAL BACKGROUND OF THE INVENTION I. Field of the Invention This invention relates to weapons and more particularly to a combination firing chamber front end seal and projectile guide. The invention herein described was made under a United States Department of the Army contract.

2. Prior Art During the firing of a weapon, the burning propellant releases propellant gases in the firing chamber. For optimum efficiency of the weapon, it is necessary to prevent escape of the propellant gases except through the weapon barrel behind the projectile. In most conventional weapons, the firing chamber may be an integral part of the end of the barrel, and expansion of the cartridge case seals the weapon chamber to prevent the propellant gases from escaping.

Recently, attempts have been made to provide caseless cartridges and weapons adapted for firing them. In a caseless cartridge there can be no expansion of a cartridge case to provide obturation. Additionally, weapons have been designed for firing caseless ammunition which provide separate firing chambers and barrels, the firing chamber abutting against the end of the barrel. In such a system, it is possible for the propellant gases to escape along the interface between the barrel end and the front end of the firing chamber.

Additionally, since it is difficult to attach a projectile to the front end of a molded propellant cartridge, it has been suggested to embed the projectile telescopically within the molded propellant cartridge body. This can present a problem of misalignment between the projectile in the cartridge and the bore of the weapon barrel. When such misalignment occurs, firing of the projectile will cause it to collide with the end of the weapon barrel, thereby reducing effectiveness of the weapon. Repeated misaligned firing can damage the weapon permanently. It is therefore desirable to have some means of correcting misalignment between the barrel bore and the projectile.

SUMMARY The above problems of the prior art are solved by this invention which provides a combination projectile guide and propellant gas seal for use in a weapon system. Preferably, the invention is utilized in connection with caseless ammunition weapons, however it is to be understood that it can be effectively utilized in other weapons.

The invention consists of two concentric tubular members having out-turned flanges at one end thereof, the flanges axially abutting along a radial interface. The out-turned flanges provide an increased diameter portion at one end of the assembly. The increased diameter portion is adapted to be received in a counterbore in the weapon barrel at the firing chamber end of the barrel. The counterbore is concentric with the bore of the barrel and preferably has an axial depth substantially equal to the axial dimension of the increased diameter portion of the assembly. In this manner, the assembly is fitted onto the end of the weapon barrel concentric with the bore thereof and with the main tubular portion of the assembly projecting outwardly from the end of the barrel into the firing chamber. The outer diameter of the main tubular portion of the assembly is slightly less than the inner diameter of the weapon chamber.

The inner tubular member of the assembly is adapted to function as a projectile guide and has an inner bore dimensioned, adjacent the flanged end of the assembly, the same as the bore of the weapon. Adjacent the end of the assembly remote from the flanged end, the bore of the inner tubular member tapers frustoconically outwardly to provide a bore entrance at the end of the assembly within the firing chamber which is larger in diameter than the bore of the weapon barrel. As the projectile enters the larger bore, it will encounter the tapered walls thereof and be redirected until it enters the portion of the bore which is dimensioned the same and concentric with the bore of the weapon barrel. In this manner, the projectile is guided into the weapon barrel bore.

An annular gap is provided between the inner and outer tubular members of the assembly adjacent the end of the assembly adapted to be received in the firing chamber, the gap communicating with the firing chamber. The outer tubular member of the assembly is adapted to provide an expansion seal against the inner diameter wall of the firing chamber. To that end, the outer tubular member is constructed substantially thinner than the projectile guide or inner tubular member and of a material which will allow radial expansion of the member under the influence of the propellant gases. The circumferential gap between the inner and outer members allows buildup of the propellant gases therein to create a pressure differential between the inner diameter and the outer diameter of the outer tubular member thereby causing the outer tubular member to expand into sealing engagement with the inner diameter of the weapon chamber.

The outer tubular member or seal member is preferably made of a material having a sufficient resiliency to return to its tubular shape immediately upon release of the pressure differential. The assembly is formed separate from the barrel or firing chamber of the weapon and is preferably received in a counterbore in the end of the weapon barrel and can therefore be easily replaced in the event of wear caused by repeated misalignment of the projectile or by long term operation of the weapon.

In an alternative embodiment a collar is threaded onto the end of a weapon barrel having an annular portion overlying the outer diameter of the out-turned flanges of the assembly to aid in retaining the assembly in position during operation of the weapon.

It is therefore an object of this invention to provide a front end firing chamber seal for use in cartridge-firing weapons.

It is another object of this invention to provide a combination projectile guide and firing chamber seal for use in weapons.

It is yet another and more specific object of this invention to provide a removable combination projectile guide and firing chamber seal comprising concentric tubular members, the inner member adapted to act as a projectile guide and the outer member adapted to seal the front end of the firing chamber of a weapon by radial expansion under pressure of the propellant gases in the firing chamber.

Other objects, features and advantages of the present invention will be readily apparent from the following detailed description of certain preferred embodiments thereof taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a cross-sectional view of the projectile guide and firing chamber seal assembly of this invention.

FIG. 2 is a front plan view of the assembly of FIG. 1.

FIG. 3 is a cross-sectional fragmentary view of the assembly of FIG. I inserted in a counterbore in a weapon barrel and projecting into the firing chamber of the weapon.

FIG. 4 is a view similar to FIG. 3 illustrating the operation of the assembly of this invention during firing the weapon.

FIG. 5 is a view similar to FIG. 3 illustrating an alternative method of attaching the assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates the combination projectile guide and weapon chamber seal assembly 10 of this invention. The assembly consists of two concentric tubular members, a projectile guide 11 which is the inner tubular member and a weapon chamber seal 12 which is the outer tubular member. Both members 11 and 12 have out-turned flanges I3 and M at their

front ends

15 and 16. The out-turned flange [3 of the projectile guide 11 increases the diameter of the guide II at the end 15. The out-turned flange 14 of the seal 12 increases the diameter of its front end 16. The increased diameter portion or

flanges

13 and 14 have an equal outer diameter and the front end 16 of the seal member 12 abuts the radial wall 17 of the flange 13. The radial wall 17 defines the side of the flange 13 opposite the end and a radial wall 18 defines the side of the flange 14 opposite the end 16 so that the increased diameter portion of the assembly is defined by the end 15 of the projectile guide 11, the outer diameters 19a and 19 b of the

flanges

13 and 14 and the radial wall 18 of the flange 14 of the seal 12.

The main portion of the assembly 10 has an outer diameter defined by the outer diameter 20 of the nonflange portion of the seal 12. The seal 12 has a relatively thin cross section and has an inner diameter 21 which is substantially equal to the outer diameter 22 of the central portion of the projectile guide 11. In the embodiment illustrated, the

ends

23 and 24 of the projectile guide 11 and seal 12 remote from the

ends

15 and 16 terminate in the same radial plane. The projectile guide 11 has a reduced diameter portion 25 having an outer diameter 26 less than the diameter 22 of the central portion. The reduced diameter portion 25 provides a circumferential groove 28 between the projectile guide and seal extending inwardly from the

ends

23, 24.

The projectile guide 11 has a central bore 30 consisting of a main portion 31 and an increasing diameter portion 32. The main portion 31 has a diameter equal to the diameter of the weapon barrel bore of the individual weapon which is to receive the assembly 10. The bore 31 extends from the end 15 into the assembly towards the end 23. The increasing diameter frustoconically shaped portion of the bore 32 extends in wardly from the end 23 and has its largest diameter at the end 23. The portion 32 tapers from the end 23 to a point where it has a diameter equal to the bore portion 31.

FIG. 3 illustrates the assembly 10 in position in a weapon adapted to fire caseless ammunition. The parts of the weapon 35 illustrated are the weapon barrel 36, the weapon barrel bore 37, the firing-chamber sleeve 38, the firing chamber 39, and a fragmentary portion of the front end of a caseless ammunition cartridge received in the firing chamber 39. The assembly 10 has its increased diameter portion 42 received in a counterbore 43 of the barrel 36. The counterbore 43 is concentric with the bore 37 and has a radial depth equal to the radial thickness of the assembly 10 so that the radial wall 44 of the counterbore has a dimension substantially the same as the end 15 of the projectile guide. The counterbore has an axial depth substantially equal to the distance between the end 15 and the radial wall 18 of the flange 14 of the seal 12 so that the radial wall 18 of the flange 14 is substantially coplanar with the end 45 of the weapon barrel 36. Therefore the assembly 10 and the weapon barrel are coaxial. Because the portion 31 of the bore 30 of the assembly 10 has a diameter equal to the bore 37 of the weapon barrel, the bores are aligned and the bore 30 provides an extension of the bore 37 extending beyond the end 45 of the barrel 36.

The sleeve 38 of the weapon chamber is adapted to abut the end 45 of the weapon barrel providing an interface 46 between the sleeve and barrel end. The sleeve 38 has an axial bore which defines the firing chamber and which receives the cartridge 40. The firing chamber 39 has an inner diameter 47 slightly greater than the outer diameter 20 of the seal 12. The sleeve 38 overlies the portion of the assembly 10 which extends beyond the end 45 of the barrel 36. In this manner, the assembly 10 projects into the firing chamber 39. The firing chamber is dimensioned so that the cartridge 40 will abut or be in close spaced relation to the

end

23, 24 of the assembly when the weapon is in operative condition ready to fire. It is to be noted that FIG. 3 illustrates a caseless ammunition cartridge 40 which has a projectile telescopically embedded in it (the projectile not shown in FIG. 3). However, it is to be understood that the assembly can be used in weapons having firing chambers different from that shown and in connection with cartridges different from that illustrated, a preferred embodiment being illustrated.

It can be seen that without the assembly 10, the propellant gases created by the firing of the cartridge 40 can escape from the firing chamber along the interface 46. This not only reduces the propellant impetus given to the projectile, but can damage the weapon by etching of the interface caused by erosion of the metal thereof created by the flow of gas. Further, in those embodiments where caseless ammunition with telescoped projectiles is used, the projectile can become misaligned with the bore 37 of the barrel 36. This may be caused by an inconsistent outer or inner diameter of the molded propellant cartridge, inaccurate fit of the cartridge within the firing chamber, or misalignment of the projectile within the cartridge. When this occurs, firing of the cartridge will cause the projectile to strike the edge created between the back wall of the barrel and the bore. This reduces the speed of the pro jectile, may damage its aerodynamic abilities, and may cause damage to the barrel.

These problems are solved through the use of the assembly 10. Firing the cartridge 40 causes the projectile to enter the bore 30 of the assembly 10 at the increased diameter end 23. If the projectile is misaligned, it will strike the sloping inner diameter of the tapered portion 32 of the bore 30, thereby redirecting it into proper aligned condition in the portion 31 ofthe bore 30.

Additionally, the assembly 10 provides for front-end obturation or sealing of the weapon chamber 39. When the cartridge is fired, propellant gases will flow around the outer diameter of the assembly 10 in the space 50 between the inner diameter 47 of the sleeve 38 and the assembly 10. Propellant gases will also enter the circumferential groove 28 between the outer diameter of the reduced diameter portion of the projectile guide 11 and the inner diameter of the seal 12. Because the area 50 is greater than the circumferential groove 28 and because some of the gases therein may escape through the interface, a pressure differential is built up between the gases in the circumferential groove 28 and the gases in the space 50 with the pressure being greater in the circumferential groove 28. This pressure differential of the gases will cause the end 24 of the seal 12 to circumferentially expand into sealing engagement with the inner diameter 47 of the sleeve 38. This position is shown in FIG. 4 where the sleeve 12 has expanded into sealing engagement with the sleeve 38 thereby sealing the firing chamber 39. The projectile 52 is illustrated in the bore 37. The design of this invention provides complete front end obturation of the firing chamber. The front end 24 of the seal member 12 is expanded into circumferential sealing engagement with the inner diameter 47 of the sleeve 38 preventing any gases from flowing around the assembly 10 in the space 50 and thereby reaching the interface 46. Further, gases entering the circumferential groove 28 cannot find an escape path between the projectile guide 11 and the seal 12 due to the tight fit between them and due to the provision of the radial wall 16 which lies within the counterbore in the barrel. Further advantageous sealing may occur by making the increased diameter flange portion of the assembly 10 and the radial depth of the counterbore greater than the inner diameter 47 of the sleeve 38 so that they extend radially beyond the inner diameter. ln that manner, any gases entrapped in the circumferential groove 28 would have to follow a tortuous path to escape from the firing chamber except through the bore 37 of the barrel 36. Such gases would be blocked in turn by the close fit between the outer diameter 22 of the central portion of the projectile guide 1 1 and the inner diameter 21 of the seal 12, right angle contact with the radial wall 16 of the flange portion of the projectile guide, right angle contact with the axial wall of the counterbore 43 of the barrel 36, and right angle contact with the front end of the sleeve 38 at the interface 46.

it can therefore be seen that the assembly 10 provides effective front end obturation of the weapon chamber while at the same time guiding the projectile into proper alignment with the weapon barrel 4. After the projectile 52 has exited from the weapon barrel, the pressure within the firing chamber 39 will have been reduced below the point necessary to cause expansion of the seal 20. The lack of pressure within the circumferential groove 28 at this point in time will allow the seal to resiliently return to its original tubular configuration. Thereafter, withdrawing the sleeve 38 from around the assembly to in-feed another cartridge 40 will cause no wearing of either the sleeve or the assembly 10.

Because the assembly 10 is a separate device not attached to either the firing chamber sleeve or the weapon barrel, it can be easily replaced if damaged or worn. In this manner, the effectiveness of the weapon is retained without expensive remachining or replacement of large parts.

FIG. 5 is a view similar to FIG. 3 illustrating an alternative method of attaching the assembly 10 to the weapon barrel 36. The assembly 10 again has its increased diameter portion received in the counterbore 43 and preferably lies approximately flush with the barrel end. The outer diameter of the end 50 of the barrel 36 is threaded as at 51 and a cup-shaped locking collar 52 having a circular aperture 53 in its bottom wall 54 is threaded over the end of the barrel. The inner diameter of the bottom wall 54 overlies the outer diameter of the flange portion of the assembly 10 thereby attaching the assembly to the weapon barrel and firmly seating it in the counterbore where it will remain irrespective of jar force created during the operation of the weapon.

Although I have herein set forth my invention with respect to certain specific principles and details thereof, it will be understood that these may be varied without departing from the spirit and scope of the invention as set forth in the hereunto appended claims.

I claim as my invention:

1. A combination projectile guide and weapon chamber seal adapted for use in cartridge-firing weapons which comprises: an inner tubular member having an out-turned flange at one end thereof and a central bore having an increasing diameter tapered portion adjacent the end remote from the flanged end, an outer tubular member adapted to be received around the inner tubular member having an out-turned flange adjacent one end thereof adapted to mate with the out-turned flange of the inner tubular member to provide an increased diameter portion at one end of the assembled combination, a circumferential groove between the inner tubular and outer tubular members communicating with the end remote from the flanged end and said outer tubular member being of thin walled resilient construction so as to be circumferentially expansible under the action of propellant gases entrapped in the circumferential groove.

2. In a cartridge-firing weapon having a barrel with a bore therethrough and a firing chamber adjacent an end of the barrel, the improvement of: a combination projectile guide and firing chamber seal detachably associated with the weapon barrel and projecting therefrom into the firing chamber, said projectile guide and weapon chamber seal comprising a first member adapted to act as a projectile guide having a bore therethrough which communicates on one end with the bore of the weapon barrel and which is coaxial with and of equal diameter to the barrel bore and which has a diameter larger than the barrel bore at the end remote from said barrel and a second member, exterior of the first member, projecting from the barrel interior of the firing chamber and normally spaced from the walls of said firing chamber, said second member expansible under pressure from propulsive gases within the firing chamber into sealing engagement with the walls of the firing chamber, whereby said second member is adapted to act as a seal for the said firing chamber.

3. The improvement of claim 2 wherein the combination guide and seal is seated in a counterbore concentric with the barrel bore in the end of the barrel bore.

4. The improvement of claim 3 wherein a threaded cupshaped collar is received on the end of the weapon barrel and has portions overlying portions of the combination guide and seal to entrap it in the counterbore.

5. A seal for use in a cartridge-firing weapon having a weapon barrel with a bore therethrough, a counterbore in an end of the barrel communicating to the bore of the barrel and a firing chamber adjacent the counterbored end of the barrel comprising: a tubular member having an out-turned flange adjacent one end, said flange adapted to be removably seated in the counterbore, said member having an internal diameter greater than the diameter of the bore and an external diameter in the nonflange portion less than the internal diameter of the firing chamber, said member projecting into the said firing chamber, portions of the said member projecting interiorly of the firing chamber adapted to circumferentially expand into sealing engagement with the inner diameter of the firing chamber under influence of the presence of propellant gases in the said firing chamber, a second member received interiorly of the said member having an inner diameter aligned with the said bore, the said inner diameter of the said second member substantially the same for at least a portion thereof with the said diameter of the said bore.

6. A combination projectile guide and firing chamber seal for use in connection with cartridge-firing weapons comprising a first tubular member having an axial bore with an increased diameter tapered counterbore at one end thereof, a second tubular member having an internal diameter dimensioned to mate with portions of the outer diameter of the first member when the first member is placed concentrically within the second member, a circumferential groove between portions of the first member and the second member open at the counterbored end of the first member and the said second member having a radial thickness and material resiliency sufficient to cause circumferential expansion of portions of the said second member when the pressure in the circumferential groove sufiiciently exceeds the pressure radially beyond portions of the said second member lying radially outwardly from said circumferential groove and to circumferentially contract when the said pressure difference is reduced.

7. The combination of claim 6 wherein the ends of the said first and said second members remote from the circumferential groove opening are adapted to be removably attached to a weapon barrel.

8. A combined projectile guide and weapon chamber seal for use in a cartridge-firing weapon having a barrel with a bore therethrough, a housing having a firing chamber therein adjacent an end of the weapon barrel, the chamber communicating with the bore, the chamber having a diameter greater than the bore and a counterbore having a diameter greater than the weapon barrel bore in the end of the weapon barrel adjacent the firing chamber, the counterbore having a diameter greater than the firing chamber, the bore, counterbore and chamber being coaxial and communicating with one another, comprising: a first tubular member having an out-turned flange adjacent one end thereof, said flange adapted to be seated in the said counterbore, said flange having an outer diameter equal to the diameter of the said counterbore, said member having an axial bore extending therethrough, said axial bore having a counterbore of increased diameter tapering inwardly from the end remote the flanged end to a constant diameter section adapted to communicate at the flanged end with the bore of the weapon barrel, said first member adapted to act as a projectile guide guiding projectiles from the firing chamber to the weapon barrel bore, said first member having a reduced outer diameter section adjacent the end of the member remote from the flanged end, said flange having an axial dimension less than the axial depth of the counterbore, a second tubular member concentric with the first tubular member having an inner diameter substantially equal to the outer diameter of the first member between the flanged end and the reduced diameter portion, said second tubular member having a flanged end adjacent the flanged end of the first tubular member, said flanged end of the second tubular member having an outer diameter substantially equal to the outer diameter of the flanged end of the first tubular member and having an axial dimension equal to the axial dimension of the counterbore less the axial dimension of the flanged end of the first member whereby the said flanged ends of the said first and said second tubular members are adapted to be seated within the counterbore of the said weapon barrel substantially filling said counterbore with the outer diameters thereof extending beyond the inner diameter of the firing chamber, the said second tubular member having an outer diameter less than the diameter of the firing chamber except at the flanged end, said second tubular member having a constant normal internal diameter, said second tubular having a having a portion thereof extending around the reduced diameter portion of the said first tubular member whereby said reduced diameter portion creates a circumferential groove between the first and second tubular members adapted to be open to the firing chamber at the end of the said first tubular member remote from the flanged end, and the said second tubular member sufficiently thin-walled and resilient to circumferentially expand into sealing engagement with the inner diameter of the firing-chamber housing when pressure in the circumferential groove sufficiently exceeds the pressure between the inner diameter of the firingchamber housing and the outer diameter of the second tubular member and to circumferentially contract when the said pressure in the circumferential groove is reduced whereby the said second tubular member is adapted to act as a firing chamber seal.

9. The combined guide and seal of claim 8 including in combination therewith a cup-shaped collar threaded over the end of the weapon barrel, the bottom wall of said cup-shaped collar having a bore therethrough having a diameter greater than the outer diameter of the nonflanged portion of the said second tubular member whereby the said first and second tubular members project through the said bottom wall, the said bottom wall contacting portions of the flanged end of the said second tubular member to entrap the said flanged ends in the counterbore.

Claims

4. The improvement of claim 3 wherein a threaded cup-shaped collar is received on the end of the weapon barrel and has portions overlying portions of the combination guide and seal to entrap it in the counterbore.

6. A combination projectile guide and firing chamber seal for use in connection with cartridge-firing weapons comprising a first tubular member having an axial bore with an increased diameter tapered counterbore at one end thereof, a second tubular member having an internal diameter dimensioned to mate with portions of the outer diameter of the first member when the first member is placed concentrically within the second member, a circumferential groove between portions of the first member and the second member open at the counterbored end of the first member and the said second member having a radial thickness and material resiliency sufficient to cause circumferential expansion of portions of the said second member when the pressure in the circumferential groove sufficiently exceeds the pressure radially beyond portions of the said second member lying radially outwardly from said circumferential groOve and to circumferentially contract when the said pressure difference is reduced.

8. A combined projectile guide and weapon chamber seal for use in a cartridge-firing weapon having a barrel with a bore therethrough, a housing having a firing chamber therein adjacent an end of the weapon barrel, the chamber communicating with the bore, the chamber having a diameter greater than the bore and a counterbore having a diameter greater than the weapon barrel bore in the end of the weapon barrel adjacent the firing chamber, the counterbore having a diameter greater than the firing chamber, the bore, counterbore and chamber being coaxial and communicating with one another, comprising: a first tubular member having an out-turned flange adjacent one end thereof, said flange adapted to be seated in the said counterbore, said flange having an outer diameter equal to the diameter of the said counterbore, said member having an axial bore extending therethrough, said axial bore having a counterbore of increased diameter tapering inwardly from the end remote the flanged end to a constant diameter section adapted to communicate at the flanged end with the bore of the weapon barrel, said first member adapted to act as a projectile guide guiding projectiles from the firing chamber to the weapon barrel bore, said first member having a reduced outer diameter section adjacent the end of the member remote from the flanged end, said flange having an axial dimension less than the axial depth of the counterbore, a second tubular member concentric with the first tubular member having an inner diameter substantially equal to the outer diameter of the first member between the flanged end and the reduced diameter portion, said second tubular member having a flanged end adjacent the flanged end of the first tubular member, said flanged end of the second tubular member having an outer diameter substantially equal to the outer diameter of the flanged end of the first tubular member and having an axial dimension equal to the axial dimension of the counterbore less the axial dimension of the flanged end of the first member whereby the said flanged ends of the said first and said second tubular members are adapted to be seated within the counterbore of the said weapon barrel substantially filling said counterbore with the outer diameters thereof extending beyond the inner diameter of the firing chamber, the said second tubular member having an outer diameter less than the diameter of the firing chamber except at the flanged end, said second tubular member having a constant normal internal diameter, said second tubular having a having a portion thereof extending around the reduced diameter portion of the said first tubular member whereby said reduced diameter portion creates a circumferential groove between the first and second tubular members adapted to be open to the firing chamber at the end of the said first tubular member remote from the flanged end, and the said second tubular member sufficiently thin-walled and resilient to circumferentially expand into sealing engagement with the inner diameter of the firing-chamber housing when pressure in the circumferential groove sufficiently exceeds the pressure between the inner diameter of the firing-chamber housing and the outer diameter of the second tubular member and to circumferentially contract when the said pressure in the circumferential groove is reduced whereby the said second tubular member is adapted to act as a firing chamber seal.