WO2008091245A2

WO2008091245A2 - Thin-walled cartridge casing with exterior reinforced head end

Info

Publication number: WO2008091245A2
Application number: PCT/US2007/001479
Authority: WO
Inventors: William A. Dittrich
Original assignee: General Dynamics Ordnance And Tactical Systems - Simunition Operations, Inc.
Priority date: 2007-01-19
Filing date: 2007-01-19
Publication date: 2008-07-31
Also published as: WO2008091245A3

Abstract

A cartridge or ammunition casing is made of two principal components, one providing the outer casing sidewall and the other, in the form of an external reinforcing member or plug, defining the head end. The casing sidewall extends inwardly into the plug and through a primer well opening formed therein to engage these two parts together. The casing sidewall may have two diameters formed by the method of first forming a cylindrical tube of reduced diameter and then expanding a portion of that tube to a larger, final, diameter. This same technique may be used to produce a rimless casing with an extraction groove.

Description

TITLE: Thin- Walled Cartridge Casing with Exterior Reinforced Head End

This invention pertains to the field of ordinance. More particularly, it addresses a cartridge casing and process for manufacturing the same which is directed towards cartridge casings typically used in small and artillery caliber ammunition.

Background to the Invention

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 on firing and act as a seal against the chamber wall of the weapon 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. Lastly, the casing must not burst on firing.

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. This extension exposes a portion of the cartridge to the risk of bursting on firing.

As observed in US Patent 2,774,283 by Harvey, the bolt face of such a typical weapon supports and rests against the base or head of the cartridge on firing but does not completely provide support for sealing-in the gases. The casing has therefore traditionally been made heavier at the rear or head end to prevent it from bursting in the locations where it is not fully supported or enclosed.

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 US Patent 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.

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 on occasion 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. US Patent 3,765,297 by Skochko et al), but those methods have not been shown to be fully reliable.

Much work has also gone into investigation of plastic as an alternate material for cartridge casings. 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 US Patent 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 inserted and/or 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 of the plastic sidewall to the metallic base cup is a problem.

Multipart casings having an all-plastic sidewall, (US Patents 4,726,296 by Leshner/Donnard & 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. 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 US Patent 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.

US Patent 1,082,975 to Rylands describes a cartridge casing with a simplified construction and reduced cost. It describes a rimmed 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 Berdan-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 '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. US Patent 933,030 to Funk describes a rimmed center fire cartridge which comprises a 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 '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.

The '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.

United States patent 6,959,647 to Reynolds et al. depicts in Figure 12 a rimmed cartridge with a two piece casing having a cylindrical casing side wall that terminates in its lower portion in a closed base end, except for primer gas vent holes formed in the base end. The lower portion of the casing sidewall is inwardly radially indented and fitted into an exterior cup-shaped seat that defines the head end for the casing. Priming composition is contained between the cup-shaped seat and the base end of the casing sidewall. The priming composition is not centrally located but is spread-out over the interface between the seat and base end of the casing side wall so that the cartridge can function in either rimfire or center- fire modes. Accordingly, this casing configuration is not adapted to accommodate a standard center-fire primer. US patent 640,856 to Bailey describes a multicomponent rimmed cartridge casing with a casing sidewall made of paper that is inwardly indented towards the head end and then at its terminal base end extends continuously inwardly to the boundary of the wall of the primer well formed in the head end piece. The head end piece is in the form of a plate with no cylindrical extension in the direction towards the forward end of the casing. No portion of the paper casing sidewall extends along or through the primer well. An internal insert or "breach piece" with a tubular extension or "nipple" fitted into the primer well defines the cylindrical wall of the primer well. This nipple extension extends through the primer well to a countersunk depression on the head end of the casing where its outer end is "upset", serving to clamp the parts together. The outer end of the nipple terminates in the countersunk depression on the head end. A primer composition is contained within the nipple and a separate T- shaped anvil extends into the interior of the nipple.

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.

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

One object of the invention is to provide a cartridge casing for either rimmed or rimless ammunition, but preferably rimless ammunition, with an outer casing wall that is protected or reinforced around the exterior 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't supported completely on the outside of the casing by the weapon chamber and bolt interface. A further object is to provide a casing made of two principal parts that are so connected as to withstand the shock of having the extractor of a fire arm withdraw the spent casing from the chamber of weapon without the parts separating.

According to the invention in one aspect, a thin-walled cartridge is provided having a continuous casing sidewall that extends towards the head end of the casing and inwardly near the head end to the boundary of a primer recess formed in a separate part defining the head end. The head end is defined by an exterior support member or reinforcing "plug" with a centrally located primer well opening. This exterior plug is seated on and coupled to the outside of the case at its head end.

The exterior plug, particularly in the case of rimless ammunition, is dimensioned to extend sufficiently forwardly along the cartridge casing to ensure that the forward end of the exterior plug extends at least to and preferably a little beyond the open portion at the breach of a firearm into which the cartridge is to be loaded. As is customary in rimless ammunition, the exterior plug has an extractor groove formed therein adjacent to the head end. The purpose of the exterior reinforcing plug is to reinforce the thinner sidewall of the casing in the region where the head end of the casing is exposed outwardly at the breach on the firearm. At the same time, the casing wall preferably extends with seamless continuity inwardly from its maximum circular cross-section, over the inner surface of the external plug, preferably generally conforming to the shape of such plug until such casing wall extension or "casing shell" reaches the boundary of the primer well opening. At the primer well opening such casing shell then extends in a cylindrical form through the central opening present in the external reinforcing plug. This casing shell extension thereby defines the periphery of a primer well, permitting insertion of a primer cap therein. Use of a casing shell made of one piece that totally contains the propellant upon ignition, except for the small opening at the base of the primer well, protects the exterior plug from exposure to propellant gases.

The casing wall extension defines the actual walls of the primer well.

That is, the casing shell extends along the side of the wall of the central opening in the external plug, reaching outwardly to the exterior face of the head end of the cartridge and thus forming the cylindrical walls of the primer well. The central hole in the exterior plug defining the primer well opening, through which the terminal end of the casing shell is inserted, is dimensioned (taking into account the thickness of the casing shell) to allow the inner dimension to be about the diameter of the primer cap. This allows a primer cap to be fitted therein with a friction fit.

In defining the primer well, a portion of the casing shell or a protrusion therefrom may make a slight inward excursion or extension at the inner end of the primer well opening so as to provide an annular rim that underlies the primer well. This rim, with or without the insertion of an additional, optional, perforated, annular insert or reinforcing disk, can serve to provide a seat for the primer cap. Such optional reinforcing disk, if present, is perforated by a relatively small vent hole to provide access for primer gases to ignite propellant present within the casing. The slight inwardly extension in the casing shell wall around the base of the primer well supports this disk on one side while the primer cap holds the disk in place on its other side, when present, such disk can be formed with a dimple and 2 smaller holes to provide an anvil as in a Berdan primer.

As an alternative to having a portion of the casing shell protrude with an extension to provide an annular rim that underlies the primer well, the external plug can have a similar annular rim around the primer well opening formed therein. The casing shell extension is dimension to fit through the annular interior opening in this rim. Thereafter, with the parts seated in intimate communication, the casing shell extension may be expanded to define the inner walls of the primer well. This expansion serves to lock the two components together. An additional, perforated, annular insert or reinforcing disk can be optionally fitted in the primer well to provide a seat for a primer cap.

The portion of the casing shell extension defining the primer well side walls can additionally, after extending through the primer well opening in the external plug, terminate in an external flange or crimp that expands outwardly and overlies a portion of the head end of the casing around the primer well opening in the external plug in a rivet-like manner. This extension may also or alternately serve to couple the exterior plug and casing wall extension together. A small countersunk recess in the exterior face of the head end may be provided to receive the riveted end of the casing shell. The assembly procedure for these components, according to several variants, consists of inserting the base end of the outer casing shell into the exterior plug and either: expanding the casing shell extension within the primer well opening to engage an annular rim formed on the external plug; or bending- over the protruding edge of the casing shell extension within the countersunk recess to engage the perimeter of the primer well and hold the casing shell and exterior plug together, or both.

A cartridge casing made according to the configuration of the invention has the advantage that the only material exposed to the propellant on firing is the material of the casing sidewall, including the casing shell inward extension at the head end. This permits use of materials in the exterior support member that could react with high temperature propellants, e.g. aluminum. The exterior plug acts as a reinforcing base to support the thinner shell in the portion of the cartridge not contained within the chamber of a weapon. The continuity of the material of the inner shell eliminates the risk of propellant gases escaping through a joint around the outer periphery of the casing. The presence of the reinforcing exterior plug permits the use of thin- walled materials for the casing shell, including in particular brass, steel, stainless steel and aluminum. And the exterior plug itself can be made of aluminum, combined with a brass, steal or stainless steel casing shell which serves as a barrier between the aluminum of the plug and particularly hot gases forming within the case.

Preferably, the head end of a case according to the invention is formed with a thickness that is on the same order as that of the casing sidewall. This permits use of an alternate mode for shaping the form of the case as described further below. By reason of the fact that thin- walled materials are used, the metal forming operation for producing casings in accordance with the invention is simplified, permitting the use of lighter tooling.

According to a preferred variant, the exterior plug is a solid body which includes the primer well opening and receives the casing sidewall extension/casing shell along its inner surface. The plug is shaped to generally bear against the outer surface of the casing shell sufficiently to support the casing sidewall against the pressures arising from propellant gas generated on firing of the ammunition.

According to a preferred variant, the casing shell is of one piece in the sense of being "integrally formed" with the casing sidewall. The expression "integrally formed" indicates that there is continuity of material between the casing sidewall and the casing shell. This feature conveniently integrates with the metal forming procedure described further below.

According to another preferred variant, the outer plug engages with the outer surface of the casing sidewall through a pressed tight fit or interference fit along at least a portion of the interfacing surfaces. For this purpose, a portion of the inner surface of the plug may be of a circular, cylindrical form, receiving a complementary portion of the casing shell with an intimate fit. One advantage of a tight pressed or interference fit, e.g. a contact between the inside surface of the outer casing sidewall and the outside surface of the plug that establishes a substantial frictional engagement, is to provide support against propellant gas on firing. Another advantage of providing such a coupling between the plug and casing sidewall is that it will help ensure that both parts are rigidly connected to each other and can be reliably loaded and extracted as a unit from the chamber after firing. A particularly stable connection between the casing shell and plug can be effected by providing the casing shell and plug each with a first short cylindrical interface portion terminating with a second tapered interface portion wherein the two parts are seated together. In this variant, the plug may have an inwardly tapering interface surface, tapering towards the head end of the case. Further or alternately, an outwardly protruding ring may be formed into the casing sidewall, extending into a corresponding groove in the exterior plug just below the upper boundary of the plug, to prevent shifting of the plug. Or the forward end of the plug may be crimped slightly into a groove formed in the casing sidewall.

The primer well for receiving a primer is defined by the portion of the casing shell extension that extends through the primer well opening in the external plug, terminating at the head end preferably in the external flange. As indicated above, to seat a primer cap therein, a portion of the casing shell on the interior end of the primer well can be extended inwardly to form an annular rim at the base of the primer well; or the casing shell extension may be expanded outwardly within a primer well opening in an external plug having an annular rim. A Boxer-type primer cap or the like with its own internal anvil may then be fitted into the primer well. Alternately, a perforated disk (perforated to allow venting of primer gases into the main interior of the case) with a raised portion to serve as an anvil may be seated on the annular rim to receive a Berdan-type primer cap.

The thickness of the casing sidewall may be equal to or greater than the thickness of the casing shell. As a further preferred variant, the outer casing sidewall and casing shell can have nearly the same relatively constant thickness. Either result can conveniently be obtained by forming such portions from a single piece of material which initially has a thickness which is near or equal to that of the final thickness for such parts.

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 US Patent 2,193,245 by Buxton but preferably being thinner than normal, is re-formed to provide the outer sidewall of the casing, and casing shell. This may be achieved through progressive stamping operations.

The preferred method of fabrication of the casing sidewall and casing shell is to start the forming process from a thin sheet of metal rather than from a thick billet. The metal is formed by standard metal forming stamping and drawing procedures into a cylinder with a closed base end. In the prior art, this end is quite thick, corresponding to the thickness of the starting billet. In the prior art the flow of metal through the forming operation requires that the metal be "stretched-out" from the original thick billet to form the thin- walled casing sidewall. In the prior art, the head end remains thick.

According to the presently described method of the invention, the original sheet-metal billet is thin. The formation of the casing sidewall occurs through progressive forming operations that fold-up the sheet metal inwardly towards becoming the cylindrical casing sidewall. In the folding-up process the metal is compressed in some regions. However, as more metal accumulates through the folding-up process, the metal is also stretched-out to take-up the excess quantity and form the final, thin-walled, casing sidewall. This type of sheet metal forming can be done with lighter tooling than in the prior art fabrication of standard brass casings.

A further variant method of fabrication according to the invention involves the above process extended by the following additional steps. In forming the cylindrical tube of the casing sidewall with a thin- walled head end, the process is carried-out to a stage where the tube diameter is less than the final diameter of the casing. Then, to produce the complete casing, the under-size cylindrical portion is expanded in the region, which is to have the final diameter of the casing. This expansion enlarges the diameter of the cylindrical portion to the final diameter of a full casing. The unexpanded portion of the casing sidewall will then have a reduced diameter suited to fit within the interior of a circular cylindrical portion of a correspondingly dimensioned exterior plug.

Once a casing is so formed, it may optionally be followed by a reduction in the diameter of the forward end of the casing as where, in the case of a 5.56 or 7.62 mm cartridge, a shoulder is to be formed on the casing. But the main diameter of the casing is established by expanding an undersized cylindrical precursor to form the final casing sidewall.

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 initial piece of 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. The foregoing has generally been directed to the fabrication of cartridges for use in ball ammunition. The same technology also has application in respect of the manufacturer of blank ammunition.

In the case of a blank cartridge, it is appropriate to simulate the Standard length of a ball round to ensure reliable loading. It is always necessary to correctly orient a cartridge that is being loaded into the chamber of a weapon. In the case of weapons that cycle automatically, surfaces are provided adjacent to and preceding the breach to direct the front end of the cartridge containing the projectile into alignment with the chamber. It many situations, the placement of these guiding surfaces assumes that the cartridge being loaded is of the standard length associated with the ball round.

One convenient way of providing blank ammunition of the appropriate length is to extend the casing sidewall forwardly and then crimp the forward end of the cartridge inwardly, terminating at the same distance from the head end as the location of the forward tip of a projectile in a ball round. This configuration of cartridges known in the prior art based upon the forming of brass cartridges.

In making a blank cartridge in this manner all of the procedures described above for re-forming a metal blank into a shaped cartridge casing are applicable. Further, in order to reinforce the head end of a blank cartridge made in the manner described, and internal plug may be seated against the inside surfaces of the head end, the extraction groove, and a portion of the casing sidewall. This internal plug is provided with a primer well opening to receive a primer cap inserted through a hole in the face of the head end. Such internal plug may have a shape similar to the external plug described herein, except that it is the outside surface of the internal plug which mates intimately with the inside surface of the casing sidewall of a blank round. Such contact should be sufficient to exclude high-pressure propellant gas generated on firing from bursting the outside wall of the casing. Such an internal plug is preformed to fit within the casing at the head end so as to not interfere with the extraction groove formed in the other casing surface

By fabricating a casing for a blank round according to the above procedures, the final casing has a relatively similar thickness in the cylindrical sidewall as in the end plate at the head end. This distinguishes it from standard ammunition. The result is a lower-cost fabrication procedure for making ammunition, and particularly a procedure that is less expensive to manufacture. Further, the actual round is reduced in weight from a round of equivalent size having a thickened base end. These advantages are especially present in the case of a blank round that can be used in place of standard ammunition for training purposes.

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

Figure 1 is an exploded cross-sectional side view of a casing according to the invention wherein the sidewall portion of the casing is being into an external plug, the external plug having an annular rim at the base of the primer well. Figure 2 is an assembled depiction of Figure 1.

Figure 3 is a variant on Figure 1 wherein the casing shell portion of the casing side wall and exterior plug each have complementary cylindrical portions.

Figure 4 is a variant on Figure 1 wherein the casing shell provides an annular rim at the base of the primer well.

Figure 5 is a pictorial depiction of a disk to serve as a seat for a primer at the base of the primer well.

Figure 6 is a side view of a blank round with a crimped forward and made in accordance with the manufacturing procedure of the invention and containing an internal plug to supply of reinforcing to the sidewall of the round.

Description of the Preferred Embodiment

In Figure 1 a casing sidewall 1 extends towards the head end 2 of a casing 3 and then extends inwardly near the head end 2 to the boundary 5 of a primer opening 6 formed in a separate part 7 defining the head end 2. The head end 2 is defined by an exterior support member or reinforcing "plug" 7 with a centrally located primer well opening 6. This exterior plug 7 is seated on and coupled to the outside of the case 3 at its head end 2.

The exterior plug 7, particularly in the case of rimless ammunition having an extraction groove 11 as shown in Figure 1 , is dimensioned to extend sufficiently forwardly along the cartridge casing sidewall 1 to ensure that the forward end 10 of the exterior plug 7 extends at least to and preferably a little beyond the open portion at the breach of a firearm into which the cartridge is to be loaded.

The casing wall 1 extends with seamless continuity inwardly from its maximum circular cross-section, over the inner surface of the external plug 7, conforming to the shape of such plug 7 until such casing wall extension or "casing shell" 8 reaches the boundary 5 of the primer well opening 6.

At the primer well opening 6 such casing shell 8 then extends in a cylindrical form through the central opening present in the external reinforcing plug. This casing shell extension 4 thereby defines the periphery of a primer well, permitting insertion of a primer cap (not shown) therein.

The casing shell extension 4 defines the actual walls of the primer well.

That is, the casing shell extension 4 extends along the side of the wall of the central opening 6 in the external plug 7, reaching outwardly to the exterior face of the head end 2 of the casing 3 and thus forming the cylindrical walls of the primer well for receiving the primer cap with a friction fit.

To define the primer well as shown in Figure 4, a portion 12 of the casing shell 8 protruding there from extends at a location which will eventually be at the inner end 5 of the primer well opening 6 to provide an annular rim 12 that underlies the primer well. This rim 12, with or without the insertion of an additional, optional, perforated, annular insert or reinforcing disk 14, Figure 5, can serve to provide a seat for the primer cap. Such optional reinforcing disk 14, if present, is perforated by relatively small (e.g. .078 inches) vent holes 50 to vent primer gases and may be provided with a raised portion 16 to serve as an anvil.

As an alternative to having a portion of the casing shell 8 protrude with an extension to provide an annular rim 12 that underlies the primer well, the external plug 7 can have a similar annular rim 12A around the inner boundary of the primer well opening 6. This is shown in Figures 1-3. The casing shell extension 4 in this case is dimension to fit through an annular interior opening in the rim 12 A. Thereafter, with the parts seated in intimate communication, a portion 4A, as shown in Figure 2, of the casing shell extension 4 is expanded to define the inner walls of the primer well. This expanded portion 4 A serves to lock the two components together. In this configuration as well, a reinforcing disk 14, can be optionally fitted in the primer well to provide a seat for a primer cap.

The portion 4 A of the casing shell extension defining the primer well side walls can additionally, after extending through the primer well opening 6 in the external plug 7, terminate in an external flange 15 that expands outwardly and his crimped to overlie a portion of the head end 2 of the casing 3 around the primer well opening 6 in the external plug 7 in a rivet-like manner. This extension 15 may also or alternately serve to couple the exterior plug 7 and casing wall extension 4 together. A small countersunk recess 16 in the exterior face of the head end 2 may be provided to receive the riveted end of the casing shell 8.

The plug 7 is shaped to generally bear against the outer surface of the casing shell 8 sufficiently to support the casing sidewall against the pressures arising from propellant gas generated on firing of the ammunition. The outer plug 7 engages with the outer surface of the casing shell 8 through a tight fit along at least a portion of the interfacing surfaces. In Figure 3 portion 18 of the inner surface 17 of the plug 7 may be of a circular, cylindrical form, receiving a complementary portion 19 of the casing shell 8 with an intimate fit. As further shown in Figure 3 the plug 7 may have an inwardly tapering interface surface 20, tapering towards the head end 2 of the case 3.

The thickness of the casing sidewall 1 may be equal to or greater than the thickness of the casing shell 8. As a further preferred variant, the outer casing sidewall 1 and casing shell can have nearly the same relatively constant thickness.

Once a casing is formed as described above, it may be followed by a reduction in the diameter of the forward end of the casing 3 as shown in Figure 2 to form a shoulder 21 and forward extension 22 of reduced diameter the casing.

Materials which may be used for the outer cylindrical sidewall and casing shell 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 outer plug, depending on the propellant used, appropriate materials include aluminum, brass, steel, stainless steel, and appropriate polymeric plastic materials. The use of stainless steel or a pre-coated carbon steel should reduce the need for a final coating on the case. Using only two principal 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 casing sidewall and casing shell 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 casing sidewall and casing shell of adequate strength surrounded by a separate external 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. .012-.025 inches of 300 series stainless, rather than the thick plate e.g. .150-.20O 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 forming stress. Proper selection of materials/processes can result in a component weighing less than the common brass casing.

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 outer 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. Figure 6 depicts a blank round 30 that may be manufactured using the same metal forming methods as described above. As shown in Figure 6, the reduced diameter forward portion 22 of the casing side wall 1 of the cartridge of Figure 2 is extended forwardly by an extension 23 and then crimped inwardly, terminating at a crimped forward end 24 located at the same distance from the head end 2 as the location of the forward tip of a projectile in an equivalent ball round.

In making a blank cartridge in this manner all of the procedures described above for re-forming a metal blank into a shaped cartridge casing are applicable. In particular, the procedure by which a cylindrical tube with a sidewall destined to form the eventual casing sidewall 1 is expanded (at a point above the head end 2, forward of the extraction groove 11) from a lesser diameter to the final diameter of the casing 3 is particularly suited to the production of a blank cartridge 30 with a rimless case 3 having an extraction groove 11.

Starting with the thin sheet-metal billet, once a cylindrical tube with a base end 2 is formed, due to the relative thinness of the tube sidewall, it is relatively easy to roll-form or otherwise press with a collet die, for example, the cylindrical tube into an interim diameter that is smaller than its final diameter by an amount necessary to form the extraction groove 11, and then re-expanded above the two the region of the groove 11 in the manner described above to form the casing sidewall 1. An internal reinforcing plug may then be seated in the head end of the casing to protect the sidewall from the pressures of exploding propellant gas.

Conclusion 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.

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.

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.

Claims

The embodiments of the invention in which an exclusive privilege is claimed are defined as follows:

1. A casing for cartridge ammunition, the casing having a head end and an interior volume for containing propellant comprising:

a) a cylindrical casing sidewall;

b) a casing shell integrally connected with the cylindrical casing sidewall and extending inwardly proximately to the head end of the casing to provide a base end to the casing shell;

c) an exterior reinforcing plug positioned to surround the casing shell and to define the exterior portion of the head end of the casing and provide support to the casing against the high pressures experienced in the firing of the ammunition, the exterior plug having a centrally located primer well opening and an inner surface directed towards the location for propellant;

d) a casing shell extension integrally formed with the casing shell extending generally along the inner surface of the exterior plug to the primer well opening to seal-off the exterior plug from propellant gas arising upon firing of the ammunition and further extending through the primer well opening in the external plug to define the interior walls of a primer well for receiving a primer cap, and e) coupling means for coupling the casing shell with its casing shell extension to the external plug.

whereby the exterior reinforcing plug is shielded from being exposed to the propellant on firing by the casing shell and the exterior plug acts as a reinforcing base to support the casing shell on firing.

2. The casing as in claim 1 wherein the exterior plug comprises an extraction groove for rimless ammunition and is dimensioned to extend forwardly along the casing shell to ensure that the exterior plug covers at least the portion of the casing exposed for access to the extraction groove when the cartridge is loaded into the chamber of a firearm.

3. The casing as in claim 1 wherein a portion of the casing shell around the inner end of the primer opening provides an annular rim that serves as a base for the primer well.

4. The casing as in claim 3 further comprising a perforated, annular reinforcing disk positioned on the annular rim at the base of the primer well to serve as a seat for a primer cap.

5. The casing as in claim 2 wherein the external plug comprises an annular rim around the inner end of the primer opening, the annular rim having a central opening through which the casing shell extension extends, the casing shell extension having a diameter within the primer opening beyond the annular rim that is larger than the diameter of the central opening in the annular rim serving to couple the exterior plug, casing wall extension and casing shell together.

6. The casing as in claim 5 further comprising a perforated, annular reinforcing disk positioned over the casing shell extension adjacent the annular rim of the exterior plug at the base of the primer well to serve as a seat for a primer cap.

7. The casing as in claim 1 wherein the casing shell extension, beyond its extension through the exterior plug primer well opening, terminates in an expanded external flange that overlies a portion of the head end of the casing around the primer well opening in the external plug in a rivet-like manner, serving to couple the exterior plug and casing wall extension together.

8. The casing as in claim 7 wherein exterior plug comprises a countersunk recess in the exterior face of the head end to receive the expanded external flange of the casing shell extension.

9. The casing as in claim 1 wherein the external plug is shaped along its inner surface to generally bear against the outer surface of the casing shell sufficiently to support the casing shell against the pressures arising from propellant gas generated on firing of the ammunition.

10. The casing as in nay one of claims 1 to 9, wherein a cylindrical portion of the inner surface of the external plug is of a circular, cylindrical form, which cylindrical portion is engaged with a complementary circular cylindrical portion of the casing shell to provide a cylindrical contact interface there between with an intimate, engaging fit so that both the external plug and casing shell are rigidly connected to each other for being reliably loaded and extracted as a unit from a chamber of a firearm after firing.

11. The casing as in any one of claims 1 or 10 wherein a conical portion of the inner surface of the external plug is of conical form, which conical portion of the inner surface is engaged with a complementary conical portion of the casing shell to provide a conical contact interface there between with an intimate, engaging fit so that the external plug provides support to the casing shell upon firing of a cartridge incorporating the casing.

12. The casing as in claim 1 comprising an outwardly protruding ring formed on the casing sidewall and a corresponding groove formed in the exterior plug for engagement with the external plug to prevent shifting of the casing sidewall and external plug with respect to each other.

13. The casing as in any one of claims 1 to 12 inclusive wherein the outer casing sidewall and casing shell have substantially the same thickness.

14. The casing as in any one of the claims 3 to 13 wherein the exterior plug has an extractor groove formed thereon.

15. A method for forming a casing for cartridge ammunition comprising:

a) providing an initial piece of sheet-metal billet having an initial given thickness;

b) forming such billet into a cup having a base end and a tubular portion through progressive forming operations that fold-up the metal of the billet inwardly towards becoming the cylindrical casing sidewall to a stage where the tubular portion has a first diameter which is less than the final diameter of the casing to be formed; c) expanding the tubular portion in the region which is to have the larger, final diameter of the casing while permitting the tubular portion having a first diameter to retain such first diameter,

to thereby provide a casing having casing sidewalls with lesser and larger diameter portions.

16. The method for forming a casing for cartridge ammunition comprising combining the casing as formed by claim 14 with an exterior plug having an interior portion with an inner surface of a circular, cylindrical form of complementary diameter to the lesser diameter portion of the casing sidewall, and fitting the lesser diameter portion of the casing sidewall into the interior portion of the exterior plug to provide a cylindrical interface with an intimate, engaging fit so that both parts are rigidly connected to each other for being reliably loaded and extracted as a unit from the chamber after firing.

17. The method for forming a casing as in claim 16 followed by the steps of reducing the diameter of the forward end of the casing sidewall to form a shoulder thereon.

18. A casing for blank ammunition to be used as a substitute for projectile- containing ammunition of a given length, the casing having a head end and a sidewall a portion of which at least encloses an interior volume for containing propellant, the casing comprising:

a) a generally cylindrical portion that forms at least part of the sidewall of the casing; b) an inward extension of the casing sidewall at the head end of the cartridge defining an extraction groove for the casing;

c) an end panel at the head end of the casing, the casing end panel having a centrally located end panel opening to receive a primer,

d) a forward extension of the sidewall of the casing terminating at a crimped end which crimped end extends to a distance from the head end which approximates the length of projectile-containing ammunition to simulate the standard length of projectile-containing ammunition and provide for reliable loading of the blank cartridge,

wherein the thickness of the casing sidewall is substantially the same in the generally cylindrical portion as in the inward extension and end panel at the head end of the casing, and wherein the generally cylindrical sleeve portion, inward extension of the casing sidewall and end panel are integrally formed.

19. A casing for blank ammunition as in claim 18 wherein the sidewall of the casing, as it extends forwardly from the cylindrical portion comprises a shoulder of reduced diameter.

20. A method for forming a casing as in claim 18 comprising:

a) providing an initial piece of sheet-metal billet having an initial given thickness; b) forming such billet into a cup having a base end and a tubular portion through progressive forming operations that fold-up the metal of the billet inwardly towards becoming the cylindrical casing sidewall to a stage where the tubular portion forwardly of the head end has a first diameter which is less than the diameter of the head end and final diameter of the casing to be formed;

c) expanding the tubular portion in the region which is to have a larger, final diameter of the casing while permitting the tubular portion forwardly of the head end having a first diameter to retain such first diameter,

to thereby provide a casing having an extraction groove located forwardly of the head end.

21. The method for forming a casing as in claim 20 followed by the steps of reducing the diameter of the forward end of the casing sidewall to form a shoulder thereon.