Abstract:
A cartridge or ammunition casing is made of two components, one forming the outer casing sleeve and head end and the other comprising a plug seated within the head end to protect the outer casing material from propellant gases. The outer cylindrical sidewall and end panel of the casing may be made of a material selected from the group consisting of stainless steel, steel, pre-coated carbon steel, brass or brass-type alloys, aluminum, hardened aluminum alloys, and suitable polymeric plastic material such as nylon derivatives and VECTRA™. The inner plug may be made of a material selected from the group consisting of aluminum, brass, steel, stainless steel, and suitable polymeric materials.

Description:
[0001]    This invention pertains to the field of ordnance. More particularly, it describes a cartridge casing and process for manufacturing the same which is directed towards cartridge casings typically used in small and artillery caliber ammunition. 
       BACKGROUND OF THE INVENTION 
       [0002]    Cartridge casings used in small caliber to artillery caliber weapons provide the function of containing the other major components of the cartridge, including propellant, projectile or bullet and primer. In addition to being a container, the casing must expand slightly and act as a seal to prevent gases, generated by the propellant, from leaking from the forward or mouth end of the casing, along the sidewall of the casing, and through the breach or bolt face at the rear of the casing. The head end of the casing must also absorb the striking force of the firing pin without deforming excessively. 
         [0003]    In the case of rimless cartridges, a portion of the head end typically will extend beyond the support of the chamber wall of the weapon barrel. This is to provide access by an extractor mechanism on the weapon bolt to engage with an extractor groove formed in the sidewall of the casing of the rimless ammunition. 
         [0004]    As observed in U.S. Pat. No. 2,774,283 by Harvey, the bolt face of such a typical weapon supports and rests against the base or head of the cartridge but does not completely provide support for sealing-in the gases. The casing must therefore be made heavier at the rear or head end to prevent it from bursting in the locations where it is not fully supported or enclosed. The drawing in that patent also describes the engagement of the extractor, which removes the casing from the weapon after firing, with the extractor groove of the casing. 
         [0005]    Conventional cartridge casings are generally manufactured from brass, steel or aluminum by a process in which a thick walled cup is formed from a coin or cylinder of metal, after which it is headed, drawn, trimmed, annealed and otherwise formed in a series of operations, resulting in the shape and physical properties required to interface with conventional weapons. A typical process used for manufacture is described by Offutt et al in U.S. Pat. No. 1,296,842. The large number of steps in the process and the scrap produced, e.g. during machining the extractor groove, substantially add to the end item cost. There have been many attempts to reduce the cost and also to reduce the weight of cartridge casings by the use of alternate materials and processes, but the majority of casings are still manufactured using materials and processes based on techniques developed nearly a century ago. 
         [0006]    The continual need for lighter weight in military applications has initiated numerous studies of aluminum as an alternate material for conventional brass and steel casings. Some success has been achieved in 20-40 mm size casings, which have been in use for nearly half a century. However, in the smaller sizes used in rifles, machine guns and other man-portable high velocity systems, aluminum has not been shown practical. Under the high pressures and physical stresses encountered in such systems, aluminum has been shown to catastrophically fail in the event of even minor material defects. The failure mode often results in ignition of the aluminum, causing a “burn through” that can be hazardous to the user. Numerous attempts have been made to mitigate this behavior through the use of coatings and ablative materials (e.g. U.S. Pat. No. 3,765,297 by Skochko et al), but those methods have not been shown to be fully reliable. 
         [0007]    Much work has also gone into investigation of plastic as an alternate material. Two part casings, using a metallic base combined with a plastic upper sidewall, have also been tried to reduce weight and cost. They have been successful in lower pressure weapons, such as shotguns. Processes for the manufacture of such metallic bases for shot shells are described by Buxton in U.S. Pat. No. 2,193,245. In such applications, the metallic head or base is formed from thin steel, brass or brass coated/clad steel strip in a progressive process, beginning with a thin coin of the metal. The plastic sidewall is then molded into the interior of the resulting base cup. Similar configurations have been tried for high-pressure casings, but they have required heavier base cups to retain the high pressures and attachment to the plastic sidewall to the metallic base cup is a problem. 
         [0008]    Multipart casings having an all-plastic sidewall, (U.S. Pat. No. 4,726,296 by Leshner/Donnard &amp; U.S. Pat. No. 4,614,157 by Grelle et al) have also been tried. Under the greater temperatures and more severe physical environments experienced in military weapons these designs have shown a propensity to fail at the joint of the plastic-to-metal base, causing jammed or damaged weapons. All-plastic cases have also not been shown to be as capable of sustaining the high pressures experienced in small caliber cartridges. Some applications have been successful, e.g. low pressure blank/training ammunition, but in general, success has not been achieved with higher pressure, conventional, ball/tracer ammunition. 
         [0009]    Steel has been used as an alternate to brass as the casing material for nearly a century. However, the process used to manufacture a steel casing requires even more operations than that used for brass. Some success has been attained (see U.S. Pat. No. 4,041,868 by Rayle et al) in reducing the weight of a steel casing through the use of higher strength boron steel in a design that minimizes the amount of steel in the head end or base area. However, this still requires performing all the major operations, including applying the lubrication coatings needed for forming steel casings from thicker initial billets. 
         [0010]    U.S. Pat. No. 1,082,975 describes a cartridge casing with a simplified construction and reduced cost. It describes a center fire cartridge comprising an outer shell that extends continuously from the cylindrical to base-end portions of the casing, and an internal base cup. This cartridge is intended to operate on the basis of a Burdan-style primer. The internal base cup, which is “formed of a single piece of metal”, is in the form of a thin, conically shaped plate that is, effectively, pleated. This base cup is positioned internally at the base of the cartridge casing at its head end and is held in position along its outer circumferential edge by an “inwardly extending circular rib rolled in the shell.” Thus the primer is held in place by the internal base cup: “the metal of the base cup is bent inwardly to form a circular pocket which receives the primer . . . . At the bottom of the primer pocket are holes  17  through which the flame of an exploded primer passes to ignite the power charge in the shell.” This &#39;975 patent provides a simplified cartridge construction having a single outer member and a one-piece internal base cup. However, the base cup is not of a design to assist the outer shell in resisting gas pressures in the vicinity of the head end particularly when exposed to the high pressures associated with modern propellants. 
         [0011]    U.S. Pat. No. 933,030 describes a center fire cartridge which comprises The casing with a cylindrical sidewall fitted into a base cup at the head end of the casing. The base cup includes a pocket for the primer of the Boxer type. As illustrated in this &#39;030 patent, the casing sidewall is fitted within a round rim at the point where it engages with the base cup. An outer, secondary head-end cup with an extended sleeve embraces both the base cup and the casing sidewall. The sleeve portion of the secondary cup extends along the casing sidewall, extending partially towards the forward end of the casing. Pressed paper surrounds the primer pocket on the inner side of the casing, extending to the inner surface of the casing sidewall. 
         [0012]    The &#39;030 patent ostensibly provides a cartridge that is not substantially reinforced or protected from propellant gas pressure at its base end because of the low structural strength of the paper filler. 
         [0013]    Accordingly, it is an objective of this invention to provide an alternate design for a lightweight and low cost cartridge casing primarily for use in the higher-pressure small caliber individual and crew-served weapons. It may also have applications in larger caliber artillery weapons. 
         [0014]    The invention in its general form will first be described, and then its implementation in terms of specific embodiments will be detailed with reference to the drawings following hereafter. These embodiments are intended to demonstrate the principle of the invention, and the manner of its implementation. The invention in its broadest and more specific forms will then be further described, and defined, in each of the individual claims which conclude this Specification. 
       SUMMARY OF THE INVENTION 
       [0015]    One object of the invention is to provide a cartridge casing for either rimmed or rimless ammunition with an outer casing wall that is protected or reinforced within the interior of the base or head end of the casing in order to resist the high pressures of propellant gases in the locations where the casing wall isn&#39;t supported completely on the outside of the casing by the weapon chamber and bolt interface. 
         [0016]    According to one embodiment of the invention the casing for ammunition in the form of a cartridge having a head end and containing propellant in its interior for use in small caliber and artillery caliber weapons comprises:
       a) a generally cylindrical sleeve portion that forms the sidewall of the casing, the casing being further substantially closed at the head end by the casing end panel having a circumferential boundary joined with the sidewall, the casing end panel having a centrally located end panel opening, preferably in the form of a well, to receive a primer, and   b) an inner reinforcing plug preferably seated against the head end to provide support to the casing against the high pressures experienced in the firing of the ammunition, the inner plug having a primer well recess formed therein and aligned with said end panel opening to receive a primer, the recess terminating in one or more perforations through the inner plug to permit gas from the primer to enter into the interior of the casing
 
wherein the inner plug extends laterally between the primer well recess and the casing sidewall whereat the plug is provided with an outwardly-directed cylindrical plug surface fitted to bear against the inner surface of the casing sidewall to seal-off the casing sidewall and casing end panel from propellant gas arising upon firing of the ammunition. Preferably said outwardly-directed cylindrical plug surface extends forwardly towards the open end of the casing, past the depth of the primer well recess.
       
 
         [0019]    According to a preferred variant the inner plug is a solid body which extends laterally between the primer well recess and the casing sidewall where the plug is fitted to bear against the inner surface of the casing sidewall to seal-off the casing sidewall and casing end panel from propellant gas arising up on firing of the ammunition. Alternately, the inner plug may be in the form of a layer which conforms to the sidewall of the primer well recess, the interface of the end panel, and an initial portion of the inner surface of the casing sidewall to seal-off the casing sidewall and casing and panel from propellant gas arising upon firing of the ammunition. 
         [0020]    According to another preferred variant, the casing end panel is joined seamlessly in a unitary manner to the casing sidewall around the circumferential boundary of the casing end. That is, the sleeve or sidewall portion of the casing and the casing end panel are preferably “integrally formed”. The expression “integrally formed” indicates that there is continuity of material between the casing sidewall and the circular casing end panel. Preferably, the outer casing sidewall and outer casing end panel are all formed from one piece of material. The thickness of the casing sidewall may be equal to or greater than the thickness of the casing and wall panel, which is converse to the configuration of most standard ammunition. This feature conveniently integrates with the metal forming procedure described further below. 
         [0021]    According to another preferred variant, the inner plug engages with the inner surface of the casing sidewall through an interference fit. One advantage of the interference fit, e.g. having a sealing, preferably voidless, contact between the inside surface of the outer casing sidewall and the outside surface of the plug, is to prevent propellant gas on firing from having access to the head end. Another advantage of providing such a coupling between the plug and casing sidewall is that it will help ensure that both parts are extracted as a unit from the chamber after firing. Alternately, to keep the plug in place within the casing, the casing sidewall may be given a slight inward taper towards its forward end, forward of the plug, after the plug is fitted in place. Further or alternately, an inwardly protruding ring may be formed into the casing sidewall above the upper boundary of the plug to prevent shifting of the plug. 
         [0022]    In a simple variant of the invention the casing end panel has a centrally located end panel opening and the inner plug provides the recess to receive a primer. According to a further preferred variant, the casing end panel is provided with an inwardly depressed, cup-shaped primer pocket or well formed therein to accept a primer. This is an alternative to having the inner plug define the primer recess. The primer well when formed integrally with the casing end panel includes a cylindrical sidewall provided by/connected to the casing end panel at the head end. Such a primer well preferably also includes a seating surface for the primer in the form of an annular base that closes-off the inner end of the cylindrical wall of the primer well, (except for a perforation therethrough to allow the primer gases to ignite propellant within the inner volume of the casing upon firing). This seating surface for the primer is also preferably an integral extension of the casing end panel. 
         [0023]    The plug is primarily seated against the inside surface of the end panel of the casing. The plug in this latter variant is preferably shaped to overlie at least a portion of the inner side of the primer seating surface formed at the base of the primer well where it may optionally be further seated. The primer gas perforations in the inner plug are aligned or are in communication with the perforation in the primer well seating surface to allow for the passage of propellant gases. In cases where the plug overlies the primer well cylindrical sidewall, the plug may be partly supported by such wall as well as by the base of the primer well. However, it is preferable that the primary support for the plug is provided by the fact the plug extends to contact securely against the inside surface of the head end of the casing. 
         [0024]    When the casing end panel extends inwardly to form the cylindrical sidewall of the primer well, it is advantageous for the plug to embrace this cylindrical sidewall of the primer well around its outside surface. This will strengthen the primer well against expansion when the primer is pressed therein, helping to retain the primer in the primer well by the friction fit. 
         [0025]    According to another feature of the invention, in the variant of rimmed ammunition the casing sidewall, at its juncture with the circumferential boundary of the end panel, extends outwardly to provide that the diameter of the end panel is greater than the diameter of the cylinder defined by the casing sidewall. This forms a protruding annular rim to provide an extraction rim for the casing. In this variant, the inner plug does not conform to the casing sidewall in the region of the annular rim. 
         [0026]    As is customary in rimless ammunition, the casing sidewall has an extractor groove formed therein adjacent to the head end. To accommodate this groove, the inner plug may itself have an annular groove, step or recess formed therein and the casing wall overlying the groove, step or recess in the plug may be deformed to fit within such space to provide an extraction groove for the casing. The fit between the casing wall within the groove and the inner plug need not be intimate, which is to say that the casing wall and the inner plug do not necessarily need to be in complete, sealing contact along the entire outer surface of the inner plug. 
         [0027]    The plug may have a straight-footed cylindrical support that extends to the inside surface of the end panel at the head end of the casing. The diameter of this cylindrical foot may be reduced from the main diameter of the plug to provide room for the formation of the extraction groove in the sidewall of the casing. The plug may also be made with its own rim at the head end portion of the cylindrical foot. Then the outer casing sidewall may be rolled or crimped over this plug-rim to lock it in place. This configuration will have the advantage of allowing the rim-forming operation to provide a sharper radius on the forward corner of the outer edge of the casing rim, stiffening the rim and providing a preferred shape to better engage with the extractor mechanism of the weapon. As a further feature to improve engagement with the extractor mechanism of the weapon, the cartridge rim, whether formed on rimmed ammunition or defining one side of the extraction groove, can be bent slightly forwardly so that it protrudes at less than a right angle from the casing sidewall. 
         [0028]    As stated above, the thickness of the casing sidewall may be equal to or greater than the thickness of the casing and wall panel. As a further preferred variant, the outer casing sidewall and end panel can be made of nearly the same relatively constant thickness. Either result can conveniently be obtained by forming the side and end walls from a single piece of material which initially has a thickness which is near or equal to that of the final thickness of the end panel. Starting with a thinner sheet of material, particularly a metal, allows formation of the cylindrical sidewall of the casing by progressive stamping operations that are not interrupted by as many annealing and lubrication treatment steps as would be required if a thicker sheet of material were used initially. This process is to be distinguished from the traditional casing forming operation in which a thick sheet of the initial material is used to form a thick head end and the thinner casing sidewall is re-formed out of the annular material around the head end. 
         [0029]    Materials which may be used for the outer cylindrical sidewall and end panel of the casing in accordance with the invention include stainless steel, steel (preferably pre-coated carbon steel to provide corrosion resistance), brass or brass-type alloys, aluminum and hardened or tougher forms of aluminum alloys, and equivalent suitable polymeric plastic materials. For the inner plug, appropriate materials include aluminum, brass, steel, stainless steel, and appropriate polymeric plastic materials. The use of stainless steel or a precoated carbon steel should reduce the need for a final coating on the case. Use of precoated steel may be able to reduce the number of operations and cost by applying the coating to the rolled steel strip in a continuous process before any forming operations are begun. Such coated strip is commonly used for shot shell bases, lamp parts, etc. to reduce costs and provide the appearance of brass. 
         [0030]    Generally, but particularly where the plug is formed of higher strength carbon steel or stainless steel, the plug may not necessarily need to be a fully solid body which extends between the primer recess and the casing sidewall (where it is fitted to bear against the inner surface of the casing side wall). Instead, it may be in the form of a sheet shaped to fit over and embrace the primer well, extending to and along the inside surface of the casing end panel at the head end, and extending upwardly along the casing sidewall in the form of an outer a cylindrical extension to this sheet. An inner plug according to this design is intended to provide a combined thickness in the casing sidewall and the base area of the casing at the head end as well as well as a sealing effect sufficient to withstand and seal-off the outer surface of the casing at its head end from propellant gas pressure. This outer cylindrical extension to the plug may be in the form of a flange that is positioned to extend upwardly towards the open end of the casing while lying against the inner surface of the casing sidewall. Preferably, this outer cylindrical extension extends forwardly of the depth of the primer well or recess. 
         [0031]    Even where a solid body is employed, this solid body may have its own forwardly directed cylindrical extension in the form of a cylindrical sleeve or flange that lies sealingly against the casing. The material forming such a flange is preferably of a dimension and sufficiently ductile to improve the seal between the plug and the casing sidewall under the pressure of expanding propellant gases. To provide this function, it may taper with reducing thickness as it extends towards the forward end of the casing. 
         [0032]    Manufacture of casings according to the invention may be achieved in a variety of manners. According to one method of manufacture, a rimmed metal base cup, initially formed from a thin coin in the manner similar to that disclosed in U.S. Pat. No. 2,193,245 by Buxton but preferably being thinner than normal, is re-formed to provide the outer sidewall of the casing, with the base panel at the head end of the casing. This may be achieved through progressive stamping operations. In the case of rimless ammunition, the inner plug, having provision for an extractor groove in the form of a plug groove or annular indentation formed in the lower portion of its outer circumference sidewall, is then pressed-in or inserted into the base portion of the casing sidewall. Then the outer casing is crimped or deformed into the plug groove to provide an appropriately shaped extractor groove for the casing. 
         [0033]    According to another method of manufacture, a rimless casing according to the invention may be similarly manufactured by progressively forming from a sheet-metal sheet a cylindrical precursor to the cylindrical portion of the casing, closed-off the cylindrical precursor at the head end by an end panel. At the circumferentially boundary between the end panel and the cylindrical wall of the precursor casing, an outwardly protruding rim is formed in the normal manner for forming a rim on rimmed ammunition. Thereafter, the precursor casing is expanded to its normal, full, diameter in the region above the location of the extraction groove which is to be present in the final rimless cartridge. Then the plug in accordance with the invention may be inserted into the bottom of the casing. In this manner, the unexpanded portion of the material of the casing sidewall defines the extraction groove. This is the reverse process from that of providing an initial casing with a full diameter sidewall and then deforming the sidewall inwardly to form the extraction groove. 
         [0034]    If a rim type casing is needed, as an alternative to forming the rim before insertion of the inner plug, such a plug of appropriate final diameter, preferably having its own rim which will ensure centering, can be inserted into the casing. The casing outer wall is then deformed at the head end to form the protruding rim by reducing the diameter of the casing above the rim present on the plug. In this metal forming operation the casing sidewall is reduced to an inside diameter which is able to mate intimately with that of the outer wall of the plug. By providing a rim on the bottom end of the plug the outer casing layer may then be rolled over this plug rim. This configuration of the invention helps ensure that the plug is locked into place inside the cartridge casing. 
         [0035]    The presence of a bottom, footing rim on the inner plug permits the outer casing rim, either on rimmed ammunition or as the rim bordering an extraction groove, to be formed with a sharper forward corner which is better suited for engagement by the extraction finger on a firearm. 
         [0036]    In another embodiment, the outer surface of the casing is made entirely of polymeric plastic which is molded to extend continuously along the cylindrical sidewall sleeve portion of the casing and around the head end to form the end panel and embrace the cylindrical inner plug. This outer surface may be extended to define a primer well in the head end. This is the reverse of conventional practice, e.g. as in shot shells, wherein the plastic sidewall is molded integrally around only the outer periphery of the metal cup forming the head end of conventional shotshells. This avoids the need for a junction for the joining of plastic and metal components at the sidewall, which has been a failure point in prior configurations. Polymeric materials such as nylon derivatives, VECTRA™, or other equivalent materials can be used as the polymeric plastic material. In this variant as in all cases of the invention, the inner plug provides protection for the polymeric plastic outer surface of the casing at its head end against the effects of propellant gases. 
         [0037]    In the embodiment consisting of a plastic outer cartridge casing, the casing can be formed so as to fit into a groove present in the plug that is shaped to receive the plastic outer layer with an intimate fit. Alternately, a right-circular cylindrical plug can be used having no “notches” into which the plastic casing can be intimately pressed. Instead, the plug has an inward step at its bottom end to receive the inwardly deformed outer layer, but is not shaped in the form of a groove to receive the plastic outer layer with an intimate fit. In this case, an extractor groove can be formed into the plastic outer shell, independently of the shape of the plug. This latter shape could be formed by injection molding the plastic over the plug, or by inserting the plug after injection molding of the outer casing. 
         [0038]    Using only two pieces to form the supporting casing members provides an advantage over other prior art processes because it permits the use of a sheet metal stamping-type process for the outer member, which is simpler than the common casing production process wherein a thick metal disk must be drawn and stretched in several separate operations to provide The casing with a thick base and a thin sidewall. The use of a thin walled, outer shell or sleeve of adequate strength surrounding a separate internal reinforcing plug can closely mimic the function of existing brass or steel one-piece casings, while providing a number of advantages over prior art casings. First, the outer component in the current invention can be produced from a thin sheet of metal e.g. 0.012-0.025 inches of 300 series stainless, rather than the thick plate e.g. 0.150-0.200 inches as typically used for an equivalent normal cartridge casing. This permits use of a manufacturing process similar to those used in tin can and stamping manufacturing operations, thereby reducing or eliminating eliminate intermediate annealing operations. This process also permits using smaller, lighter weight, multi-station forming presses which will reduce cost. Some annealing of the forward end of necked-down cartridges may still be required to relieve less than the common brass casing. 
         [0039]    The current invention also permits the use of relatively thin stainless steel or pre-coated carbon steel as an outer material, providing the strength and even the appearance of brass with the proper coatings. By using a somewhat more expensive per pound, but lighter, aluminum inner plug to provide the reinforcement normally provided by a heavier-based brass or steel conventional casing head end, the current invention can provide savings in overall weight. 
         [0040]    The foregoing summarizes the principal features of the invention and some of its optional aspects. The invention may be further understood by the description of the preferred embodiments, in conjunction with the drawings, which now follow. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0041]      FIG. 1  is a cross sectional side view of a prior art 5.56 mm cartridge case. 
           [0042]      FIG. 2  is a cross sectional side view of one embodiment of the cartridge case of the current invention. 
           [0043]      FIG. 3  is a cross sectional side view of a cup used as the initial member in the production of the cartridge case of  FIG. 2  in one embodiment. 
           [0044]      FIG. 4  is a cross-sectional side view of the cup of  FIG. 3  after the formation of the primer pocket and part of the extractor groove. 
           [0045]      FIG. 5  is a cross-sectional side view of a reinforcing plug. 
           [0046]      FIG. 5A  is a cross sectional side view of an alternate embodiment of the plug of  FIG. 5  having a small rim its base end. 
           [0047]      FIG. 5B  is a cross sectional side view of another alternate embodiment of a plug of  FIG. 5  having a circumferential recess. 
           [0048]      FIG. 6  is a cross sectional side view of the cup of  FIG. 4  which is being expanded with an expansion punch and supporting die. 
           [0049]      FIG. 7  is a cross sectional side view of the case sleeve of  FIG. 6  with the reinforcing plug in place. 
           [0050]      FIG. 8  is a cross sectional side view of a cartridge using the cartridge case of the invention as depicted in  FIG. 1 . 
           [0051]      FIG. 8A  is a cross-sectional side view of a rimless cartridge using a reinforcing sheet rather than the reinforcing plug of  FIG. 8 . 
           [0052]      FIG. 8B  is a cross-sectional side view of a rimmed cartridge using a reinforcing sheet rather than the reinforcing plug of  FIG. 8 . 
           [0053]      FIG. 8C  is a cross-sectional side view of a rimmed cartridge using the reinforcing plug as depicted in  FIG. 5A . 
           [0054]      FIG. 8D  is a cross-sectional side view of a rimmed cartridge using a reinforcing plug that has no rim and wherein the outer rim is provided entirely by the case sleeve. 
           [0055]      FIG. 8E  is a cross-sectional side view of a rimless cartridge using a reinforcing plug as depicted in  FIG. 5B , wherein the case wall is depressed into the plug&#39;s annular recess. 
           [0056]      FIG. 9  depicts a cartridge using the cartridge case of the current invention which is chambered within a firearm. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0057]      FIG. 1  shows a typical prior art cartridge case. A case of this type is formed by the progressive drawing of an initially thick “coin”, and as a result has a thick base member  200  at the head end  202  and a tapered cylindrical sidewall  203 . 
         [0058]      FIG. 2  depicts a first embodiment of the cartridge casing  1  of the current invention. A cartridge casing  1  is provided with an cylindrical outer case member  2  having a cylindrical sleeve portion  8  and an end member  7 . A cylindrical reinforcing plug  10  is located at the head end  202  of the cartridge casing  1 . The reinforcing plug  10  is arranged such that it will provide additional strength to the sleeve-like case member  8  in the base area of the cartridge casing  1  needed to withstand the higher stresses in that area of the cartridge casing  1  occurring as a result of gas expansion at the area of the cartridge casing  1  where the case  1  is not substantially supported by the barrel or bolt assembly. 
         [0059]    In order to produce the outer case member  2 , in one embodiment, the process for the outer component begins with a strip of metal from which a coin is punched. The coin is then held circumferentially as it is initially pressed through a die with a punch to form a cup with a sidewall having about half the height of the cup diameter. That cup is then pressed through a number of smaller and smaller (e.g. 5) dies to further elongate it while reducing its diameter to that described by  FIG. 3 . 
         [0060]      FIG. 3  depicts the elongated steel cup  30  from which a cartridge casing  1  is to be formed in one embodiment of the invention. The cup  30  initially has a diameter which is less than the final required diameter, such that the sidewalls of the cup  30  may be expanded through the use of a die and punch or other appropriate tooling device to conform to the shape which is desired in the end product. By using a cup  30  having a generally uniform thickness, it is typically easier to stamp-form the material into the final shape of a casing. 
         [0061]    The cup  30  is further flattened at the head end to form the rim  4  or pinched-in to form an extractor groove  12 . Then, one or more punches are successively pressed in from the head end against rigid pocketed punches inside the case to form the primer pocket  3  and hole. All the operations are normally performed sequentially on a multiple station (e.g.  13  station) progressive die stamping press, with completed straight walled case components with rims  4  and primer pockets ( FIG. 4 ) falling off the end of the press. Alternately, the straight cup  30  of  FIG. 3  is left larger in diameter than the desired diameter of the end product and pinched in at the bottom after forming the primer pocket  3  defining a primer well to form a complete, straight-walled, rimless case  1  having an extractor groove  12 . After plug insertion, the case is tapered; the mouth is formed and trimmed on a separate press(s). 
         [0062]      FIG. 4  depicts the cup  30  of  FIG. 3  which has been headed. The heading step has provided a small annular protrusion  4  at the head end of the outer case member  2 , which is to form a portion of the extractor groove used in most military weapons. An end panel opening  31  to accommodate a primer in the form of a primer well or pocket  3  has been formed, said primer pocket  3  having a centrally located passageway  6  to allow a gas evolved by the detonation of the primer  25  contained within the primer pocket  3  to reach a propellant  22  which is located further towards the front end of the cartridge casing  1 , within the sleeve-like sidewalls  8  of the cartridge case  1 . 
         [0063]      FIG. 5  depicts one embodiment of a reinforcing plug  10  to be inserted into the cartridge cylindrical sleeve portion  8  to rest against the end member or end panel  7  of the outer case member  2 . The reinforcing plug  10  is provided with a primer-accommodating recess  13  which is dimensioned to mate with the primer pocket  3  that is formed in the outer case member  2 . Such primer-accommodating recess has one or more generally centrally located bores  44  which permit gas evolved during the ignition of the primer  25  to come into contact with the propellant  22  and to ignite such propellant  22 . 
         [0064]    The reinforcing plug  10  is dimensioned so as to extend from the wall of the primer pocket  3  to at least the innermost diameter of the extractor groove  12 , such that when the reinforcing plug  10  is inserted into the cartridge casing outer member  2 , it becomes frictionally locked into place through an interference fit between the outer circumference of the plug  10  with the inside surface of the generally cylindrical sleeve portion  8  of the outer case member  2 . A similar fit may exist between the inner circumference of the primer recess  13  of the plug  10  and with the sidewalls which define the primer pocket  3 . 
         [0065]    The plug  10  may include a cylindrical flange  11  at its front end which extends forwardly from the reinforcing plug  10  further into the outer case member  2 . The cylindrical flange  11  is preferably formed such that it is tapered towards the generally cylindrical sleeve portion  8  of outer case member  2  in such a manner, combined with the ductility of the material, to permit it to expand slightly to conform more intimately with the generally cylindrical sleeve portion  8  of the outer case member  2  when exposed to the pressures that arise from the ignition of the propellant  22  in order to ensure that propellant gas does not pass between the outer case member  2  and the reinforcing plug  10 . 
         [0066]    In an alternate embodiment of the invention (not shown), the end panel opening  31  does not extend to the inside of the cartridge casing  1  in the form of a primer pocket  3 , but instead is a hole in the end member  7  which, in combination with the primer recess  13  found in the reinforcing plug  10 , forms a primer accommodating recess to accept a primer cap. 
         [0067]      FIG. 5A  depicts an alternate embodiment of a reinforcing plug  10 A having a small rim  14  at its base end. Such a rim  14  may be enveloped by the outer case member  2  in order to ensure that the reinforcing plug  10  is retained in its position in relation the outer case member  2 . Forming the rim  14  in this manner also facilitates providing the rim with the sharper inside corner. 
         [0068]      FIG. 5B  depicts another alternate embodiment of a reinforcing plug  10 E for use in rimless ammunition, the plug  10 E having a circumferential recess  15  into which the outer case member  2  can be forced in order to provide an extractor groove  12  and to ensure proper retention of the reinforcing plug  10 E in relation to the outer case member  2 . 
         [0069]      FIG. 6  depicts the outer case member  2  of the invention after having had its diameter expanded through the use of an expansion punch  16  and a supporting die  17 , while still located within said punch  16  and die  17 . A supporting member  18  holds the cartridge casing  1  in place while the punch expands the outer casing member  2  . The case now has a complete extractor groove  12 . If the case is to be a rimmed case, the initial cup  30  may be provided such that it is initially of the correct diameter. In such a case, a rim  14  would be formed by crimping the head end of the cartridge casing  1 . 
         [0070]      FIG. 7  depicts the outer case member  2  after it has been expanded through the use of the punch  16  and die  17 . In this figure, the case is provided with the reinforcing plug  10  which may be held in place by an interference fit or through the use of an adhesive or by crimping the outer case member  2  to provide an inwardly-directed annular rim or “bump” (not shown) to limit the motion of the plug along the central axis of the cartridge casing  1  and to improve the sealing properties of the reinforcing plug  10 . Alternatively, the flanges  11  of the reinforcing plug  10  may be “flared” outwardly in order to ensure that the interference fit is secure. 
         [0071]      FIG. 8  depicts a cartridge  20  which uses the cartridge casing  1  of the current invention. The cartridge is provided with a propellant  22  located within the case, a primer  25  containing primer cap  23  has been inserted into the end panel opening  31  and is held within the primer well  13 . A bullet  21  has been inserted into the mouth of the projectile. The cartridge  20  comprises the reinforcing plug  10  of  FIG. 5 , having an extractor groove  12  formed within the outer casing member  2  which is partially supported by the reinforcing plug  10 . 
         [0072]      FIG. 8A  depicts a cartridge head end having an alternate plug or reinforcing member  26  which has been formed out of thinner sheet material than in the previously mentioned embodiments of the reinforcing plug  10  which are substantially “solid” and which extend fully from the primer pocket  3  to the outer case member  2 . The strip  26  is shaped to substantially conform to the inner perimeter of the outer case member  2 . Such a strip may be formed through the use of simpler stamping machines when compared to the methods or forming the previously mentioned reinforcing plugs  10 . 
         [0073]      FIG. 8B  depicts a rimmed cartridge head end which has an alternate plug or reinforcing member  26  which reinforces and supports the rimmed head end of the cartridge casing  1  in a substantially similar fashion to that of  FIG. 8A . The rim  40  of this embodiment is formed by crimping the outer cartridge member  2  near the base end of the cartridge casing  1 , and there is no supporting member extending from the reinforcing member  26  into the rim  40 . In a similar variant of the invention, the reinforcing member  26  may also be crimped to form the rim  40  such that the rim  40  is provided with additional support. 
         [0074]      FIG. 8C  depicts a rimmed cartridge head end which has a reinforcing plug  10 C that has a base end which is substantially in the shape of a right circular cylinder. The outer case member  2  is crimped to form a rim  40  that can be used by the casing ejection mechanisms which is typically found in firearms which use rimmed ammunition. In this variant, the rim  40  is formed solely from the outer cartridge member  2 , that is to say that there reinforcing plug  10 C is not an integral part of the rim  40 . 
         [0075]      FIG. 8D  depicts a rimmed cartridge head end which has a reinforcing plug  10 D that has a base end which is provided with a small annular rim  14  that extends around its circumference. The outer case member  2  is arranged to conform to the peripheral shape that is provided by the reinforcing plug  10 D, and the plug rim  14  in combination with the outer case member  2  forms the rim  40  to be used in extraction mechanisms in firearms which use such cartridges. Although  FIG. 8D  depicts a rimmed cartridge, a rimless cartridge could 
         [0076]      FIG. 8E  depicts a rimless cartridge head end which is provided with a reinforcing plug  10 E which has a circumferential annular recess  15 . The outer case member  2  is pressed into the annular recess  15  of the reinforcing plug  10 E in order to help restrain the reinforcing plug  10 E and to provide an cationextraction groove  12  to allow the firing mechanism. This embodiment is unlike the embodiment shown in  FIG. 8 , as it provides additional support for the crimped ridge  4  of the extractor groove  12  which engages with the extractor mechanism and may provide additional support in the head end of the cartridge case  1 . 
         [0077]      FIG. 9  depicts a cross section of cartridge  20  using the cartridge case of the current invention which is in place in chamber of a firearm, showing that certain sections of the head end of the cartridge  1  are not supported by the structure of the firearm. The barrel  100  of the firearm substantially supports the generally cylindrical sleeve portion  8  of the cartridge casing  1  while the end panel  7  of the cartridge casing  1  is supported by the bolt assembly  101 . This section of the cartridge  1  which is not supported by the firearm&#39;s structure has its structural strength increased by the reinforcing plug  10 . 
         [0078]    The outer case member  2 , if made of metal, may be alternatively formed from thin strip or coin in the manner as a typical a shot shell base cup. The casing material preferably comprises a strong, ductile metal, such as brass, steel, brass coated steel, or any other similarly strong, ductile metal. The process of forming the outer case member  2  may alternatively be performed conventionally through the use of progressive die stamping and drawing presses, beginning with constant thickness strip. This process is repeated to elongate the case, as depicted in  FIG. 1B  and the case is finally headed, as shown in  FIG. 1C  to provide a rim  5  at the base end of the elongated case  4 . 
         [0079]    It would also be desirable to use polymeric materials or plastics as the outer case member  2  or as the reinforcing plug  10  or sleeve  26 . In such cases, it would be possible to form the outer case member  2  out of plastic material which is moulded around a reinforcing plug  10 . 
         [0080]    The inner reinforcing plug  10  is typically fabricated using common crafting practice, by casting, molding, or cold heading. This reinforcing plug  10  is preferably of a stronger material than the outer case member  2 , such as steel, or certain plastics. It may also be made aluminum, in which case the outer case member  2  would provide protection from the “burn-through” often experienced with all-aluminum cases. 
         [0081]    The above process, involving the combination of a reinforcing component or plug  7  with an outer case member  4 , permits the use of a much thinner strip material to be used for the outer case  4  than that used in conventional cartridges. It also permits the use of bulk pre-coated or clad materials, eliminating the need for the costly coating operations required for materials other than brass. 
         [0082]    A configuration similar to that described with reference to  FIG. 4  is also practical for designs using an outer casing made of a suitable plastic composition instead of the previously mentioned suitable metal material, as depicted in  FIG. 6 . In this instance, the plastic outer casing  16  may be molded around the inner plug  7 , which may be metallic, to provide increased strength in the head or base area of the cartridge  1 , which is hard to achieve with lower strength plastics. Molding around the higher strength plug eliminates the need for a joint of the two materials and obviates the potential failure point at the juncture, which is common in prior art. 
       Conclusion 
       [0083]    The foregoing constitutes a description of specific embodiments showing how the invention may be applied and put into use. These embodiments are only exemplary. The invention in its broadest and more specific aspects is further described and defined in the claims which now follow. 
         [0084]    These claims, and the language used therein, are to be understood in terms of the variants of the invention which has been described. They are not to be restricted to such variants, but are to be read as covering the full scope of the invention as is implicit within the invention and the disclosure that has been provided herein. 
         [0085]    While the present invention has been described with respect to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that other variations and modifications can be effected within the scope and spirit of the invention.