Plastic Cartridge Case

Abstract

A plastic cartridge whose ballistics are equivalent to existing metallic cartridges and which can be fired in existing firearms. A non-expanding metal head is securely attached to the breech end of the plastic casing by compressively squeezing the rear end of the plastic casing between a metal head and a second metallic member, either an annular support member plus a primer or by the primer itself. The plastic casing is preferably formed by drawing at least the front end of the casing and then necking down the mouth portion. The preferable plastic materials for cartridge casings include polycarbonates, polysulfones, and blends of plastics, e. g. a blend of polyethylene and polycarbonate, a blend of polyethylene and polysulfones, and alloys of polysulfones and polycarbonates.

Description

This invention relates to cartridges for firearms, particularly to cartridges having plastic body casings with metal heads attached to the breech ends of the cartridges, and the method of attaching the metal heads to the plastic body casings. Another aspect of this application relates to the drawing of certain plastics and blends and an alloy of plastics which heretofore had not been cold worked for ammunition purposes.

Although shotgun shells made of biaxially oriented plastic materials have been on themarket for about 10 years, e. g. as shown in U.S. Pat. No. 3,103,170, issued to Covington et al., on Sept. 10, 1963, there has been no real use of thermoplastic materials, either injection molded or cold worked, in high-powered rifle or center fire ammunition. Probably the main reason for this is that explosive pressures generated in center fire ammunition are much greater than in shotgun shells, e. g. about 50,000 psi as compared to 10-11,000 psi for shotgun shells. The operating requirements have just been too much for the various plastic center fire shells developed up to now except for some miscellaneous training or practice cartridges where the pressures are even less than in shotgun shells.

If the operating requirements for ammunition for single-shot high-powered rifles are demanding, the demands for automatic weapons, e. g. the M-16 rifle or machine guns, are even more so because of the high rate of loading, firing, extraction, and ejection which require mechanically strong casings and thermally stable and resistant casing material because of the heat generated in the guns by the rapid, automatic firing.

The search for suitable cartridges to replace the conventional brass or other metal case cartridges has gone on for a long time. In recent years this search has been accelerated because of the scarcity and high cost of brass. Primary emphasis in recent years has been focused on: (1) caseless ammunition in which the projectile does not have any cartridge casing and where the propellant is either located within the projectile or attached to it by some attaching or adhesive means; (2) combustible cartridge casings which are designed to be completely combustible while in the gun, and (3) expendable cartridge casings which are not combustible but which are designed to be completely expelled from the gun along with the projectile.

The present invention relates to another approach which includes the advantages of: (1) having less weight than conventional ammunition; (2) being less expensive to manufacture; (3) avoids use of critical materials such as brass or aluminum; (4) utilizing an extractable cartridge casing; (5) being interchangeable with conventional ammunition in existing guns; (6) being strong and heat resistant enough to be used in automatic weapons, and (7) requires less propellant powder for equivalent ballistics than conventional ammunition probably because of the thermal insulation properties of the plastic cartridge.

The major object of this invention is to provide a plastic-bodied cartridge which has sufficient strength to withstand the handling, storing, and firing requirements of modern firearms.

Another object of the invention is to provide a unique plastic casing to metal head attachment and the method of attaching thereof.

Another object of the invention is to provide a plastic-bodied cartridge which is suitable for high-powered center fire use.

Another object of the invention is to provide a plastic-bodied cartridge which will provide ballistics which are equivalent to conventional ammunition and which can be fired in existing firearms without modifying the forearm.

Another object of the invention is to provide a drawn-plastic casing in which the mouth end is necked down and cold worked to provide additional strength.

Another object of the invention is to provide a drawn-plastic casing which utilizes plastics, or blends or alloys of plastics, which have not been cold worked previously for ammunition purposes.

Another object of the invention is to provide plastic cartridges which are suitable for the demanding requirements of automatic weapons.

Other objects will be apparent from the specification and drawings in which:

FIG. 1 is a sectional side view of a loaded cartridge which incorporates the present invention.

FIG. 2 is a sectional side view of the molded plastic slug prior to being drawn.

FIG. 3 is a sectional side view of the plastic casing after drawing.

FIG. 4 is a sectional side view of the drawn plastic casing of FIG. 3 with a battery-cup type metallic member positioned in the primer cavity.

FIG. 5 is a sectional side view of the drawn plastic casing of FIG. 4 with a metallic head member positioned thereon.

FIG. 6 is a sectional side view of the drawn plastic casing of FIG. 5 with the front end necked down to form a smaller diameter mouth portion.

FIG. 7 is a sectional side view of the drawn plastic casing of FIG. 6 having a primer positioned in place.

FIG. 8 is a side elevation of the equipment used to draw the plastic slug.

FIG. 9 is a side elevation of the equipment used to neck down the mouth end of the cartridge casing.

Referring now to the drawings, FIG. 1 illustrates a loaded round of ammunition 10 in which the elongated body casing 12 is made of a suitable plastic material, e. g. polycarbonate. Other thermoplastic materials are also suitable and will be discussed later.

Plastic casing 12 has a main body portion 14 which is necked down at its front end 16 to form a mouth portion in which projectile 18 is secured by a force fit or any other conventional manner.

A transverse wall 20 closes off the body casing 12 adjacent to the breech end 22 thereof and includes a flash hole opening 24 therein. Integrally formed with the transverse wall 20 and projecting rearwardly to the breech end or breech face of the cartridge is a realtively thin-walled, annular skirt or flange member 26. The inner periphery 26A of the skirt 26 and the rear wall surface 20A of the transverse wall 20 (see FIG. 4) define a primer cavity 28 in which a battery-type metal cup or annular support member 30 is positioned in force-fitting relationship. Co-operating with cup 30 in placing the annular skirt 26 in compression is a metal head member 32 which engages the outer periphery 26B of skirt 26. Positioned within cup 30 in force-fitting relationship is a metallic primer 34 which assists in putting the plastic annular skirt 26 in compression. Positioned within the main body portion is a propellant means 36. It should be appreciated that skirt 26 should be thin enough so that the skirt can be put in compression by the action of the metal head 32 and the cup 30.

Although FIG. 1 shows the metal head-plastic casing attachment as it applies to a center-fire type cartridge, in this case the 5.56 mm, it should be noted that the invention could also be used with shotgun shells or pistol cartridges where the outer periphery of the metal head could either be flush with the outer periphery of the body 12 (as shown) or it could extend outwardly of the body cavity.

In the embodiment shown, the metal head 32 is made of hardened steel (RC 45-50) which has a yield strength of about 110,000 psi in order to prevent head expansion into unsupported areas under firing pressures of about 50,000 psi. Obviously, for other firing pressures other unyielding or non-expanding head members may be suitable.

The battery type cup or annular support member 30 is also made of metal, preferably brass, copper, steel, or any other suitable metal which is rigid enough to co-operate with the steel head 32 to put the plastic annular skirt under compression but which nevertheless will flex under firing pressure to expand outwardly against the skirt to act as a gas seal. The primer 34 can be made of any metallic materials of which conventional primers are made, e. g. brass, steel, copper, etc.

Although FIG. 1 shows the use of a battery-cup type of support and a primer, it has been found that for many uses a suitable casing-head attachment can be effected by omitting the battery cup and having the primer inserted directly against the inside periphery of the skirt to co-operate with the rigid head to put the skirt under compression. However, it has been found that for severe conditions, such as automatic fire, the addition of the battery cup is useful in preventing primer blow-out and in reinforcing the head-casing attachment.

FIGS. 2 through 9 illustrate another aspect of the invention, i.e. the drawing of the molded casing slug 12A (shown in FIG. 2) to the elongated and drawn casing 12B (shown in FIG. 3) and finally necked down to the finished cartridge casing 12 (shown in FIG. 6). Although the dimensions are not shown on the drawings, the breech end of the finished casing is substantially the same as the original molded slug whereas the plastic slug is elongated in an axial direction as well as expanded outwardly so as to decrease the wall thickness of the body at the mouth end. The cold working of the plastic slug improves the tensile strength of the finished casing as can be seen below. In addition to polycarbonate casings, other plastics were used to make body casings, including various blends and alloys of plastics.

TABLE I

TENSILE TESTS ON DRAWN PLASTIC ALLOYS

Before After ALLOY Drawing Drawing (Loading Rate 2"/Min.) 100% Polyethylene 4,100psi 5,500psi 98.75% Polyethylene 1.25% Polycarbonate.sup.1 4,400psi 5,700psi 97.5% Polyethylene 2.5% Polycarbonate 3,900psi 6,200psi 95% Polyethylene 5% Polycarbonate 4,300psi 5,800psi 62% Polyethylene 38% Polycarbonate 5,500psi 9,200psi 33% Polyethylene 67% Polycarbonate 6,280psi 7,800psi 16% Polyethylene 84% Polycarbonate 7,310psi 9,700psi 8% Polyethylene 92% Polycarbonate 7,139psi 9,100psi 4% Polyethylene 96% Polycarbonate 9,380psi 16,100psi* 1% Polyethylene 99% Polycarbonate 10,600psi 17,600psi 90% Polyethylene 10% Nylon 3,900psi 4,400psi 100% Nylon 9,200psi 21,900psi* 100% Arylon 7,500psi 11,600psi 10% Polysulfone 90% Polycarbonate 11,900psi 20,200psi* 25% Polysulfone 75% Polycarbonate 11,900psi 21,100psi* 50% Polysulfone 50% Polycarbonate 12,500psi 20,200psi* 100% Polycarbonate.sup.2 10,900psi 19,950psi* 100% Polysulfone 10,950psi 19,650psi* *Cases were fired as retrofit cases.

The polyethylene mentioned above is a high-density polyolefin of the type sold by E. I. du Pont de Nemours and Company as ALATHON 7320. The polycarbonate.sup.1 is a high molecular plastic sold by the General Electric Company as LEXAN 101-111. The polycarbonate.sup.2 is a low molecular weight plastic better suited for thin wall use and is sold by the General Electric Company as LEXAN 141R. ARYLON is a polyaryl ether sold by Uniroyal as T-3198 and was too brittle for this use. The polysulfone used is sold by the Union Carbide Company as P 1700 and has excellent temperature resistance.

The polyethylene is added in small amounts to make a blend with polycarbonate and polysulfone (although not listed above) in order to make the plastic blend compatible with solvents and the environment, e. g. to relieve stress cracking. When too much polyethylene is added, the blend becomes too brittle.

The addition of polysulfone to polycarbonate results in improved temperature resistance. The two plastics mix together to form an alloy and result in a homogeneous mass as opposed to the blend of polyethylene and polycarbonate or polyethylene and polysulfone where the plastics do not mix or form into a homogeneous mass. Thus, the polysulfone and polycarbonate can be mixed in about equal proportions without causing brittleness.

FIG. 8 shows a plastic slug 12A positioned on a vertically movable punch 36 before the punch and slug are moved through the die means 38 so as to elongate and expand at least the front end of the casing. This particular method of drawing is not new and has been used for years in drawing brass cases so it does not appear necessary to go into detail on the drawing process.

FIG. 9 shows a die means 40 in position around casing 12 just after necking down the mouth end of the casing. Again, this particular operation is not novel and thus it does not appear necessary to enlarge the specification with extraneous matter which does not add to the understanding of the invention being claimed. This type of equipment is clearly shown, for example, in drawing aluminum cases in the U.S. Pat. No. 3,498,221, issued to R. W. Hilton et al., on Mar. 3, 1970.

Although shotgun shells made of injection molded polycarbonates are presently on the market, it is not known that polycarbonate or polycarbonate blended or alloyed with other plastics have been cold worked before to form cartridge cases. Although polyethylene has been drawn, impact extruded, etc., to form strengthened or oriented plastic casings, the amount of recovery of polyethylene in necking down the mouth end of the present invention prevents or seriously curtails its use for center fire ammunition because the mouth will not fit tightly against the projectile. Where the mouth is open or not necked down, such as in shotshells or pistol cartridges, polyethylene is satisfactory. Moreover, the novel casing-to-head attachment of the present invention is compatible with polyethylene casings. The real advantages of polycarbonates and polysulfones or alloys of either of these with each other or blended with polyethylene are in the improved yield strengths obtainable, their high resistance to heat, and their ability to retain dimensions after being cold worked. By using polycarbonates with polyethylenes, we improve the long storage characteristics of polycarbonate. Casings have been made, as shown in the above table, having dimensions which permitted successful firing of as much as a 14-round burst in an M-16 rifle which was not modified in any manner to accept, fire, extract or eject plastic cartridges. Heretofore, injection molded casings have been made although at a sacrifice of ballistics or by modifying the guns.

The physical characteristics of the preferred plastics which contribute to their acceptable performance over known plastics such as polyethylene. These characteristics, which are measurable, are higher tensile strength, higher heat deflection temperature, and higher flexural modulus.

Although high density polyethylene can be cold worked to very high tensile strengths, the amount of cold working in the present instance does not result in sufficient tensile strength in polyethylene to be suitable for the purpose intended. Also, as explained above, the amount of recovery of polyethylene in necking down the mouth of the casing rules out the use of polyethylene.

These properties are measurable and known and are listed for example in the Modern Plastics Encyclopedia for 1968-69, Volume 45: No. 14A, October 1968, published by McGraw-Hill Inc. From this publication, we note the following values listed: ##SPC1##

Claims

What is claimed is:

1. A cartridge comprising a one-piece casing made of thermoplastic material which is substantially non-combustible under normal firing conditions, said plastic casing having a tubular body portion with a rear breech end and a forward mouth end, said tubular body portion being substantially closed off adjacent its breech end by an integral transverse wall portion and open-ended at its forward mouth end, a relatively thin-walled annular flange projecting rearwardly from said transverse wall portion and extending to the breech end of the cartridge, said annular flange having a diameter less than the diameter of said tubular body portion, a head means made of rigid metallic material in close-fitting engagement with the outer periphery of said annular flange, a metallic annular support positioned on the opposite side of said flange from said head means and co-operating therewith to place said plastic flange in compression, primer means frictionally located within said annular metallic support so as to exert additional compressive pressure against said flange, and a flash hole opening in said transverse wall portion which permits access from said primer means to the interior of the tubular body portion, said rigid metallic head means having sufficient yield strength so as to prevent permanent expansion of the head upon firing of the cartridge.

2. A cartridge as recited in claim 1 in which said metal head is made of hardened steel having a hardness ranging from about RC45 to about RC50.

3. A cartridge as recited in claim 2 wherein at least the forward mouth end of the tubular body portion has been cold worked in order to decrease the thickness of the tubular body wall and increase the strength characteristics of the forward mouth end, said forward mouth end being necked down to a smaller diameter in order to accommodate a single projectile.

4. A cartridge having a drawn plastic cartridge casing, said casing comprising a tubular body portion having a front mouth end and a rear breech end, said front mouth end being necked down to form a smaller-diameter mouth portion in which a single projectile means is positioned, a transverse wall portion integral with said tubular body portion and located adjacent to but spaced from the breech end of the casing, an annular ring means integral with and projecting rearwardly from said transverse wall portion, said ring means being held in compression by an outer rigid metallic head member and a separate inner flexible metallic member.

5. A cartridge as recited in claim 4 in which said necked-down mouth portion has been cold worked more than any other portion of the plastic cartridge casing and thus has improved strength properties over the remaining portions of the casing.

6. A cartridge as recited in claim 5 wherein said outer metallic head is made of material which is substantially unyielding under the intended pressure and said inner metallic member is made of material which is rigid enough to co-operate with the rigid head to put the annular plastic ring in compression but still flexible enough to permit the inner member to expand outwardly against the annular plastic ring upon firing to act as a gas seal therewith.

7. A cartridge having a drawn plastic casing, said casing having a tubular body portion and a front mouth portion which has been elongated in an axial direction as well as expanded outwardly so as to decrease the wall thickness of the body at the mouth end thereof, and to provide additional strength thereto, said mouth portion being necked down to provide an opening which is of lesser diameter than said tubular body portion, a single projectile secured in said mouth opening, said plastic casing being made of a thermoplastic material selected from the group of plastics and blends of plastics having high impact strength, dimensional stability, high flexural modulus, and high deflection temperature, consisting of polycarbonates, polysulfone, blends of minor portions of polyethylene with polycarbonates, blends of minor portions of polyethylene with polysulfone, and alloys of polysulfones and polycarbonates