Reinforced Lightweight Cartridge

Abstract

The firing obturation of lightweight military cartridges fabricated from a aterial other than brass can be considerably improved by the inclusion of a thin-walled cup in the head portion of the case prior to forming the required exterior taper thereof. Since the cup is fabricated from a more deformable material than that of the case, the tapering of the latter produces radial recovery forces in the mouth of the cup which serve to increase the total pressure imparted to the cartridge case sidewalls by the pressures generated during the firing of the cartridge thereby accelerating the obturation of the case in the firing chamber to a greater degree along the portion coextensive with the cup mouth than along the remainder of the case.

Description

BACKGROUND OF THE INVENTION

This invention relates to small arms ammunition and is more particularly directed to tapered cartridge cases fabricated of materials other than the customary brass.

The constantly increasing scarcity and cost of copper as well as the need for a reduction in the weight of conventional brass cartridges has led to their manufacture from such diverse materials as molded plastics, aluminum, or steel. While these efforts to provide an adequate substitute for brass have met with varying degrees of success in ammunition designed for use in sporting arms, such has not been the case in military firearms designed to fire high pressure cartridges at relatively high rates of sustained fire. For example, where the cartridge cases are fabricated from aluminum and are joined by steel links into a continuous articulated belt, the exit of the ammunition from the magazine and the delinking action required during the feeding thereof into the firing chamber of the gun frequently results in considerable scratching and nicking of the exterior surfaces of the cases. Since the wall thickness of aluminum cases is often as low as 0.010 inches, any visible scratch or other indentation generally produces a weakened area which is unusually prone to rupture or "burn-through" during the expansion imparted to the case by the relatively high pressures and hot gases generated upon the firing of the cartridge. In the event the break in the cartridge case occurs prior to completion of the normal obturating contact thereof with the interior wall surface of the firing chamber, the consequent escape of the hot and corrosive discharge gases produces an extremely rapid erosion of the firing chamber, the face of the firearm bolt and the tip of the firing pin. Obviously, any deterioration in the ability of the closed firearm breech to seal against the escape of the discharge gases during the period of peak pressure is extremely dangerous to the operator of the firearm.

Other difficulties encountered in the use of cartridges fabricated from materials of lighter weight than brass are the lack of adequate strength in the head portion of the cartridge case and the cartridge feeding and delinking problems caused by the fact that, contrary to conventional cartridges with brass cases, the projectile portion is significantly heavier than the case portion thereof, thereby causing the center of gravity of the total round to be unfavorably located more forwardly in the cartridge.

SUMMARY OF INVENTION

Accordingly, it is an object of this invention to provide an improved cartridge for firearms wherein the base or head portion of the case is internally reinforced by a separate insert fabricated from a material having greater deformability qualities than the material utilized for the case.

Another object of the present invention resides in the provision of a cartridge as aforesaid wherein the internal reinforcing means serves to improve the rapidity with which the rear or head portion of the case will expand into obturating contact with the interior wall surfaces of the firing chamber.

Still another object of this invention is to provide a reinforcing means for a cartridge which is capable of accelerating the expansion of the contingent portion of the cartridge case to minimize the rearward escape of high pressure gases in the event of any rupture or burn-through in the walls of the cartridge case.

An important object of this invention resides in the provision of a reinforcing means in the rear end of a cartridge case in a manner which will insure maximum rapidity of obturation in the firing chamber of a gun along the portion of the case coextensive with the forward portion of the reinforcing means.

It is an additional object of this invention to provide a cartridge wherein the aforesaid internal reinforcement of the case portion is also utilized to compensate for the forward relocation of the center of gravity which would otherwise have resulted from the use of a lighter material than brass for the cartridge case.

It has been found that the foregoing objects can be readily accomplished in forwardly tapered cartridges intended for military use by providing a thin-walled cup within the head portion of the cartridge case. Such cup is fabricated from a more deformable material than that of the case and is arranged to extend forwardly beyond the origination of the tapered portion of the case and terminate within the rearward half thereof. The taper required by the case is imparted thereto after the cup has been inserted in place so that the resulting reduction in the diameter of the cup mouth induces built-in radial recovery forces therein which serve to increase the total pressure imparted to the cartridge case sidewalls by the gases generated during the firing of the cartridge. As a result, that portion of the cartridge case which is coextensive with the mouth of the cup is peripherally preloaded to such an extent that the time period required to achieve positive obturation of the firing chamber in which the cartridge is fired is significantly reduced. Thus, in the event of any rupture or other perforation of the cartridge case wall forwardly of the cup, the deleterious erosion of the bolt face and firing pin tip ordinarily caused by the premature release of the discharge gases is substantially diminished. In addition, the added mass of the cup effectively compensates for the substantial forward relocation of the center of gravity of the entire cartridge which would have otherwise taken place as a result of the decreased weight obtained in the case by the fabrication thereof from a material lighter than brass.

BRIEF DESCRIPTION OF THE DRAWINGS

The exact nature of the invention as well as other objects and advantages thereof will be readily apparent from consideration of the following specification relating to the annexed drawings wherein:

FIG. 1 is a centrally broken longitudinal section of a typical lightweight military cartridge with a forwardly tapered case containing the reinforcing cup of the present invention, the stressed area produced by the final forming of the case being located between arrows A and B;

FIG. 2 is a fragmentary view of the rearward portion of the cartridge of FIG. 1 and is enlarged to show the relationship of the reinforcing cup to the interior of the case prior to the final forming of the latter;

FIG. 3 is a central longitudinal section of the rearward portion of the cartridge of FIG. 1 taken immediately following the discharge thereof in the firing chamber of a gun to show, in somewhat exaggerated fashion, the initial obturation achieved during the firing thereof; and

FIG. 4 is a sectional view taken along line 4--4 in FIG. 3 showing the additional obturation provided by the reinforcing cup in the event of any perforation in the corresponding portion of the cartridge case sidewall.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As best shown in FIG. 1, the type of military cartridge to which the present invention is particularly adapted generally consists of an elongated case 12 which is forwardly tapered from a point beginning with the annular extractor groove 14 provided in the base or head portion 16 to the start of necked portion 18 formed at the forward end thereof. While such taper is, of course, dependent on the caliber of the cartridge, a decrease in diameter of as small as 0.002 inches per inch of length has been found to be adequate in accomplishing the purposes of this invention. The sidewalls of case 12 are generally formed with a forwardly decreasing wall thickness which, in an aluminum cartridge, may reach a minimum of 0.010 inches at the junction with neck portion 18.

A forwardly opening cup 20 of a more deformable material than that of cartridge case 12 is arranged to be seated within the rearward half thereof so as to bottom against the forward face 21 of head portion 16. Cup 20 is dimensioned to slidably fit into case 12 and be seated against face 21 prior to the forming operation which imparts the required taper thereto. While cup 20 may be cylindrical in shape, the sidewalls thereof are preferably formed to terminate in a larger diameter at the open end 22 thereof than at the rear end thereof. Furthermore, the walls of cup 20 are relatively thinner than the cross-section of case 12. Thus, when the tapering of cartridge case 12 is completed, the forward or open mouth end 22 of cup 20 is radially compressed into an interference fit with case 12, thereby inducing radial recovery forces which act on the interior wall surfaces of case 12 to create a peripheral prestressed area along the portion defined by arrows A and B in FIG. 1. The bottom of cup 20 is provided with a central opening 26 therethrough communicating with the primer hole 28 in cartridge case head portion 16.

Upon the firing of the cartridge in the chamber 30 of a firearm barrel 31, the prestressed area between arrows A and B will respond more rapidly than the adjacent areas of case 12 to the pressure of the discharge gases generated within the interior thereof. As a result, the portion of the cartridge case sidewall adjacent end 22 of cup 20 will expand annularly, as best indicated at 32 in FIG. 3, into obturating contact with the corresponding interior wall surface of firing chamber 30. In addition, the firing pressures within cup 20 impart a slight degree of set-back thereto thereby exerting a wedging action on the sidewalls of case 12 which serves to increase the longitudinal extent of the annular expansion thereof.

Thus, a cartridge case constructed in accordance with the foregoing description will provide a significantly faster obturation of the firing chamber when a cartridge is fired therein than a conventional brass cartridge case with no internal reinforcement. As will hereinafter be explained, this is an extremely important factor where the cartridge case is fabricated from a lighter and weaker material than brass or is provided with a substantially thinner sidewall than a standard brass case. In either situation, it has been found that the feeding of ordinary cartridges into a firearm with sufficient capacity to achieve a sustained high rate of fire frequently produces noticeable scratches and nicks in the sidewalls of the cases. Even deeper scratches are often produced during the removal of the metal links ordinarily employed to retain the cartridges in a continuous articulated belt. As a result, the relatively thin sidewalls of these lightweight cases are unusually prone to rupture under the high pressures and resulting expansion imparted thereto during the discharge of military type cartridges. Furthermore, even if the wall of the cartridge case should possess sufficient strength to resist splitting or rupture, it has been found that the temperatures attained by the discharge gases combine with the high pressures involved to actually burn through any area weakened by a physical imperfection, especially in aluminum cases where the metal actually acts as a fuel thereby increasing the likelihood of any such burn-through.

In the event rupture or burn-through of the existing types of cartridge cases occurs before obturation of the firing chamber has been fully completed, the hot discharge gases will flow between the exterior of cartridge case 12 and the interior wall surface of firing chamber 30 into corrosive contact with the face of the firearm bolt and the tip of the firing pin. It has been found that as few as two occurrences of this gas escape will erode the firearm components to an unsafe degree. This is particularly true where the break in the wall of the cartridge case occurs at a point within the rear one-quarter of the overall length thereof.

However, the problem of inadequate obturation of the firing chamber in the event of a premature escape of the discharge gases can be successfully overcome by the reinforcing cup of the present invention installed in accordance with the technique described above. In order to achieve optimum results, it is essential that the cartridge case and cup be selected from materials such that the cup will respond more readily to diametrical expansion than the case. By way of example, where the cartridge case is fabricated from one of the materials listed in Column A, the reinforcing cup could be fabricated from the material specified in the same line of Column B.

a b cartridge Case Material Reinforcing Cup Material steel brass heat treated aluminum alloy untreated aluminum alloy aluminum epoxy resin

These and like combinations of materials will ensure the maximum degree of expansion of cartridge case 12 at the area adjacent mouth 22 of cup 20. Furthermore, if a break or split in the cartridge case sidewall, as indicated by the arrow in FIG. 4, occurs rearwardly of the mouth of cup 20, the more deformable material of the latter is actually extruded into the break, as shown at 34, to thereby seal the interior of case 12 prior to obturating contact thereof with the wall of firing chamber 30.

In addition to the foregoing, the reinforcing cup 20 also strengthens head portion 16 of case 12. This is particularly important in the base portion of case 12, which is frequently only partially supported by the walls of the firing chamber 30, since it permits a corresponding reduction in the thickness of case 12 thereby effecting a desirable decrease in the total weight of the cartridge. The reinforcement function of cup 20 also permits a desirable relaxation of the limitations ordinarily imposed on the length and depth of the various machining cuts included in the rear portion of firing chamber 30 to provide the necessary extractor and ejector grooves, feed ramps, chamfers or other projectile guide surfaces.

The foregoing disclosure and description of the invention is illustrative only. Various changes may be made within the scope of the appended claims without departing from the spirit of the invention.

Claims

I claim:

1. In a firearm cartridge having a forwardly tapered case of a material other than brass adapted to expand into obturating contact with the interior walls of a firing chamber in response to the gas pressures generated during the firing of the cartridge, the improvement of,

a substantially cylindrical reinforcing cup of a more deformable material than that of said case and disposed within the rearward half thereof, said cup having the exterior periphery thereof in forwardly increasing compressive engagement with the forwardly tapered interior surface of said case to form an interference fit therebetween, said cup also having forwardly increasing radial recovery forces therein which approach a maximum at the forward end thereof to impart corresponding obturating expansion to the portion of said case coextensive with said cup.

2. The cartridge structure defined in claim 1 wherein said case is formed of steel and said cup is formed of brass.

3. The cartridge structure defined in claim 1 wherein said case is formed of a heat treated aluminum alloy and said cup is formed of a more ductile untreated aluminum alloy.

4. The catridge structure defined in claim 1 wherein said case is formed of aluminum and said cup is formed of a thermosetting resin.

5. The cartridge structure defined in claim 1 wherein said reinforcing cup is formed with an open end of slightly larger diameter than the opposite closed end thereof to induce a maximum amount of recovery forces therein subsequent to the forming of the forward taper required by the case.

6. In a firearm cartridge having a case of deformable material other than brass adapted to expand into obturating contact with the interior wall surface of a firing chamber in response to the pressures generated during the firing of the cartridge, said case comprising,

a head,

a hollow body extending forwardly from said head to define a forwardly tapered interior, and

a reinforcing cup of a more deformable material than that of said case disposed within the rearward half of said body and having an original exterior periphery of greater diameter than the corresponding interior diameter of said hollow body prior to the tapering thereof to define an interference fit therebetween, said cup also having radial recovery forces therein increasing forwardly along the length thereof to impart a maximum rapidity of obturating expansion to said case in the vicinity of the forward end of said cup.

7. The cartridge defined in claim 6 wherein said head and said body of said case are formed of aluminum and said cup is formed of a thermosetting epoxy resin of sufficient thickness and resiliency to obturate any rupture which may occur within the portion of said body contiguous with said cup during the firing of the cartridge.