US3125924A - Charles e - Google Patents

Description

h 1964 A, A. MAYER ETAL I 3,125,924

METAL RIMMED PLASTIC CARTRIDGE CASE Filed July 16, 1962 INVENTORSI ALFRED A. MAYER CHARLES E. MILLER CHARLES O. WILLIAMS BY ATTORNEY United States Patent Ofi ice Patented Mar. 24, 1964 METAL RIMMED PLAdTIC CARTGE CASE Alfred A. Mayer, West Haven, and Charles E. Milier and Charles 0. Williams, Hamden, Conn, assignors to Giin lvlathieson Chemical Corporation, a corporation of Virginia Filed July 16, 1962, Ser. No. 209,968 3 Claims. (Cl. 86-11) This invention relates to the manufacture of ammunition and more specifically to new and improved resinous plastic cartridges for shotguns, for example, strengthened at the base by a minimum of metal about an included primer.

Shell cases of light metal and those molded of resinous plastic such as ethyl cellulose, ethyl acetate, plasticized polyvinyl chloride and polyethylene have been proposed. No matter what the material of which it is made, a shotgun shell must function not only for storing its charge, including wadding, powder and shot, without deterioration, but also for initiating the powder reliably, for projecting shot acceptably through an end closure, and for extraction and ejection from the gun. Despite firing, the case must not fracture, but because of the short-comings of many plastic cases because of embrittlement, contamination from fugitive plasticizers and dimensional instability, and/ or lack of strength, plastic construction has not been adapted extensively under the severe usage and long storage conditions encountered.

Some shooters frequently insist that the cartridges when spent be reloadable with components to the shooters own specifications. A resinous plastic shot shell, for example, is desirable wherein the fired case remains intact as long as possible and is reuseable as often as possible before any defect develops to interfere with ignition and prevent reuse.

In an effort to overcome the disadvantage of the use of various plastics and of separate components such as paper in shotgun shells, and in an attempt to realize the benefits of plastics such as polyethylene, those skilled in the art have tried the more rigid linear polyethylene. One approach has been to make the entire shotgun shell casing as one piece molded from linear polyethylene having a high degree of crystallization, a melting point of at least 125 C. and a relatively high density. For various reasons such as the differences in thickness and forces encountered in various sections of the shell, making it by plastic injection molding even by this approach has limitations and leaves much as to be desired in obtainment of the best combination of physical properties.

Another approach has been to substitute a section of tube of such linear low pressure polyethylene for the paper tube, but not until the polymer has been oriented uniformly from end to end by stretching a tube of it to develop added strength moderately and substantially uniformly in the rigid high density linear polyolefin.

It will be appreciated that ammunition cartridges are put to rigorous use as in the firing of a shotshell case where great forces are exerted with non-uniformity and over a wide range of temperatures.

Moreover, in many shotguns, the normal functioning including that of feeding, ignition, extraction and ejection is such and their normal action is so rigorous that a tremendous strain is put on the rim structure at the head of the shotshell.

One object of this invention, therefore, is to provide plastic cartridge case bodies of improved effective tensile strength together with a new and improved head structure capable of satisfactory performance regardless of such gun structure and action.

Another object is the provision of a novel process for making such cases economically by deformation of a blank of plastic in the solid state, or molding, and providing a novel metallic structure at the head.

Another object is to provide a cartridge case composed of a crystalline polymer of a thermoplastic synthetic resin formed and capped with metal in such a way that ex ceptionally high strength is obtained throughout the case and particularly at the rim adapting the case for use as a container under explosive pressure and the most rigorous extraction and ejection conditions.

Another object is to form explosive pressure cartridges having improved dimensional stability and performance particularly at the head in the region of the igniter.

Still another object is to economically provide a new and improved shotshell having a plastic side wall tubular portion, preferably of a rigid polyolefin and a metallic rim portion.

Other objects and advantages will be understood from this description of various preferred embodiments contemplated and the accompanying drawing wherein:

FIGURE 1 is an elevational side view in cross section showing the rear portion of a partially completed shotshell case in an early stage of fabrication in suitable apparatus part of which is shown in section.

FIGURE 2 is a comparable view of the whole shell of FIGURE 1 more nearly completed and in part of the apparatus of FIGURE 1 in an intermediate stage of manufacture.

FIGURE 3 is a perspective View including an elevation cross section of part of another apparatus and the shell in a still further and final stage of making of the head portion of the cartridge case or shell.

FIGURE 4 is an elevational view in longitudinal cross section showing another embodiment of the shell of this invention completely fabricated and fully loaded.

Shells having at least a plastic tubular wall, or having both the base part at the head and also the tubular wall formed integrally of plastic, particularly of high density, high crystallinity polyolefin such as the high density polyethylenes, are improved by putting the plastic in constraint at a novel metal base secured by the plastic itself over the rim in a novel way.

This is done by including a metal piece locked immediately ahead of the rim and includes displaced plastic both back of and ahead of the inwardly turned edge of the metal piece forming the base, and effecting an improved mounting at least of the base as a cap or ring for the head and even a better mounting of the primer in the head. The base is a cap or ring over the rim and over part or all of the back of the head.

In accordance with this invention the case is formed with a primer pocket in an enlarged head section of the shell either by molding or preferably by compression from a crystallizable thermoplastic such as a suitable polyolefin so that a primer cup may be inserted in the pocket forcefully after a metal base in the form of a skirted disc or washer with a short skirt forming a shallow cavity is forced back over the head until abutted and positively retained against the head in the region of the primer by locking of the edge of the skirt rolled inwardly contiguous with the front of the rim flange. A rolling-in to embed the edge into the sidewall a few thousandths of an inch is deemed adequate for the purpose in a shot shell of 12 gauge, for example. The shell head squeeze and the metal base size are selected so that the resulting exterior lateral dimensions at the head is of the correct predetermined shell heads of linear high density polyethylene, for example.

The disc is either perforated and drawn in the center to make a primer socket or is centrally cut away leaving only a ring at the shell rim.

The plastic cartridge case is shaped of a relatively rigid polyolefin, such as polypropylene of high isotacticity and preferably of polyethylene characterized by a high degree of linearity and crystallinity and by a high molecular weight above about 100,000 and preferably as high as from about 350,000 to above about 1,000,000. The polyethylene used in the tubular sidewall and base of the shell of FIGURES 13 and in the sidewall and integral base of the shell of FIGURE 4 are those produced by any one of various processes under relatively low temperatures and. low pressures of polymerization using suitable catalysts, in admixture. These contemplated have very high density and molecular weights and a high degree of linearity of the polymer chains. ,These polyethylenes, as compared to high pressure polyethylenes, have high softening or melting points and are characterized by such anihcrease in tear, tensile and yield strengths as to be classified as rigid polyethylenes.

The whole shell of FIGURE 4 or only the tube part of the case of FIGURE 2, for example, may be simply molded of such linear polyethylenes and then forced over a base wad. Tubes of shells of linear polyethylene of the low pressure type may be further treated by stretching to obtain orientation for development of addedstrength. The whole shell case of FIGURE 2 is preferably formed by compression according to copending patent application Serial No. 135,569 filed September 1, 1961.

Other plastics of equivalent character are contemplated for the tubular wall portion, either molded or compressively deformed to shape.

The shotshell bodies are formed at least in part by compression from plastic materials such as polyethylene. polypropylene and the like polymers, and/or co-polymers of the same, all finally shaped in the solid crystalline state. High density linear polyolefins specifically are contemplated for forming by compression as distinguished from forming by stretching. By confining the plastic between at least two juxtaposed surfaces exer ing pressure on the plastic and by driving plastic with plastic, final shaping to a thin-walled body is achieved advantageously from a relatively thick slug or blank of the linear polymer to attain a densification and very high increase in strength of the body, preferably so as to increase the tensile strength while decreasing the thickness gradually from the base toward the mouth of the shell.

This is done at a wide range of working temperatures below the crystalline melt temperature of the material and at speeds of compressive deformation limited to prevent an excessive rise in temperature, which is maintained preferably at an elevated temperature range less than the crystalline melt temperature. For polyethylene the working temperatures are held Well below the range from about 257 F. to about 265 F. and working occurs preferably from about 200 F. to slightly below 265 F. for available grades and makes of the thermoplastic working at about 240 F. being found suitable for most materials of this type. For polypropylene, the limiting temperature is somewhat higher and forming occurs below the much wider range from about 275 F. to about 330335 F. Somewhat higher working temperatures from about 200 F. up to slightly less than 335 F. are contemplated. By compression forming according to this procedure, stable shaping of an article by deformation can occur over a broad range of temperatures below the crystalline melt temperature rather than ina sharply limited narrow range of temperature hovering extremely closely to such crystalline melt temperature, and difficult to maintain.

The crystalline melt temperature of thermoplastic materials such as these is the elevated temperature at which all crystallinity of the polymer structure disappears and it appears clear when viewed through crossed Nichol prisms in a hot-stage microscope. The degree of crystallinity, as determined by various methods such as the X-ray diffraction method, is preferably as high as possible for each material; for polypropylene a high degree of isotacticity is also preferred along with maximum possible crystallinity.

By compressive deformation instead of stretching, necking of the thermoplastic is avoided and very high tensile strength is obtained where needed. Compression forming also allows the various parts of the finished article also to be made to different finished dimensions, an advantage which is not secured when material must be stretched out of one part depleting it to supply another as the finished product. It will be appreciated that while the super'added capping of the shell rim by a metal base gives improvement in the plastic head, this invention is especially of advantage in making in one piece the main plastic body of the shell having at least two portions differing in shape and function, at least one of which must be stronger than another or which must be thicker than other parts which nevertheless must be nearly as strong or stronger. By this invention at least a superior shell tube is formed, the head and rim stabilized dimensionally to improve the rim structure and iron out variations, and there is produced preferably a superior whole plastic shell case, sized, sealed and further rigidified at the head by the securement in the cap.

The metallic'base caps at 'least the rim of the head and is formed from a shallow cup-shaped member having a'flange on one side forming a skirt turned in and rolled over until it bites into the plastic pinching it at the head. The compressed plastic presses the embedded metal flange edge from the front as well as the rear; this leaves no edge for the extractor to catch the metal cap to tear it back off the rim. Upon firing of the shell, the plastic part in front of the rolled skirt is additionally compressed along with the plastic of the rim back of the skirt so that metal uncurling is avoided by back pressure at the front.

Where gun action permits some primer leakage safely, it is of advantage, especially with reloaded shells, to leave part of the back of the shell head uncapped. For this purpose the metal base may be perforated between the primer and rim or may be a ring as in FIGURE 4 so the shells may be reloaded and reused many times.

A one-piece body 1, having a head 2 rimmed at 3 and orificed at 4 and also having a tubular sidewall 6 shown in FIGURES 1 and 2, is shaped preferably of suitable high density'polyethylene polymerized at relatively low pressure with any one of various suitable catalysts by known processes such as the Ziegler process, and this body is put with the tube part 6 first into die bore 35 of and a flare at 36 for clearance. The diameter of bore 35 is somewhat smaller than the external diameter of the shell adjacent the base to compress the plastic of the body. A cup-shaped piece 10 of sheet metal such as brass, aluminum or steel having a thickness of about 0.010 inch, 0.013 inch, and 0.008 inch, respectively, and having a short skirt or flange 11 is placed over the head 2 and seated in cavity 33 having the round bottomed channel 34 extending all around the lip forming the entering edge of the bore 35. This piece forms a base which is then press-fitted about head 3 and its rim 4 by crimping hunter 32 coacting with the die shape 34 as bore 35 compresses the body 1l. Base 1'0 is centrally orificed at 12 preparatory to forming a primer opening at orifice 4 counterbored at 5 for the primer rim.

After this operation, body 1, as shown in FIGURE 2, is provided with the metal back 13 still orificed centrally at 14 and with rolled-in metal skirt 15 covering the front 8 of the plastic shell rim. This partially com-- pleted article is pushed out of the die 31 by support punch 38 whereupon the head again can bulge out at 9 uncompressed by the die and to tend to overlap the rolled skirt 15 and rim 8.

While supported on a punch such as 38, this partial assembly is placed in a finishing die 41 and the head is finished by sizing hunter 42, as shown in FIGURE 3.

As hunter 42 is received in the guiding counter bore 44 of the die, backing 13 is reformed in intermediate bore 45 to make the metallic base 16. This operation effects capping the shell head and beveling the flange at 17 while further extending the skirt periphery at 18 to protectively submerge the metallic edge into the body, thereby compressively surrounding the edge 18 both at 23 and 25. In the same operation, drift pin 47 and shoulder 43 re form the metal of the base 16 at the stepped primer orifice 24 to provide metal lining 19.

FIGURE 4 illustrates how any other type of base 56 is contemplated. This arrangement leaves the head of the plastic body base at 60 so that the primer 59 is directly received in plastic in receptacle 54 with frictional or adhesive retention enhanced by such radial compression effected by ring 56. As in the other embodiment, base 56 has a front beveled flange 57 with embedded edge 58.

FIGURE 4 also shows a preferred form of a completely loaded shotshell round in a plastic case 50 having the relatively thin tubular Wall 51 and the relatively massive head 52 integral therewith. Capping the head is base 56 locked both fore and aft between plastic portions 53 and 55. The shell is loaded with a suitable powder charge 66, a suitable Wad means including the flanged expansible wad 67 and filler 68 and a column of shot 69. The other end of the shell at the mouth has an evanescent type of closure '70 formed of pie-cut segments 71 between re-entrant folds all integral with the plastic body 50 and folded inwardly at 72. The arrangement pre ferred is according to US. Patent No. 2,582,124 granted to R. S. Holmes.

Capping of the head by the metallic base may be done while the metallic backing is heated so that upon cooling a shrink-fit is effected to enhance the locking and compressive action obtained.

The resulting head structure gives superior performance with the types of extractor and ejector actions encountered in shotguns.

Although the foregoing is a description of what is now believed preferred, it is to be understood that those skilled in the art may make changes all in the spirit and scope of this invention as set forth in the appended claims.

What is claimed is:

1. The method of fixing a metallic base to an ammunition cartridge case, said case comprising a tubular side wall extending from a plastic head and a plastic rim extending outwardly from said head, said base comprising a cup-shaped metallic member having a peripheral skirt terminating in an edge and adapted to be placed over said case at said rim, said method comprising forcing said case with said member into a die so that a radial compressive force is applied to the case in the region of said head, deforming said skirt inwardly around said rim so that said edge extends toward said head, releasing said force so that said case expands outwardly against said edge and said edge is partially imbedded in said case, and driving said edge further into said case While simultaneously shaping and sizing said metallic member about said rim so that said plastic at the head outwardly overlaps and completely surrounds said edge to prevent cutting and peeling of said base from said case.

2. The method of claim 1 wherein the side Wall, head, and rim are integrally formed of a crystalline polyolefin such as linear high density polyethylene.

3. The method of claim 1 wherein the head has a primer-receiving opening and the metallic member extends to said opening, and including deforming said member to line at least the rear of said opening with metal.

References Cited in the file of this patent UNITED STATES PATENTS 313,187 Dickerman Mar. 3, 1885 3,026,802 Barnet et al. Mar. 27, 1962 FOREIGN PATENTS 1,093,151 France Nov. 17, 1954 626,359 Canada Aug. 29, 1961

Claims (1)

1. THE METHOD OF FIXING A METALLIC BASE TO AN AMMUNITION CARTRIDGE CASE, SAID CASE COMPRISING A TUBULAR SIDE WALL EXTENDING FROM A PLASTIC HEAD AND A PLASTIC RIM EXTENDING OUTWARDLY FROM SAID HEAD, SAID BASE COMPRISING A CUP-SHAPED METALLIC HAVING A PERIPHERAL SKIRT TERMINATING IN AN EDGE AND ADAPTED TO BE PLACED OVER SAID CASE AT SAID RIM, SAID METHOD COMPRISING FORCING SAID CASE WITH SAID MEMBER INTO A DIE SO THAT A RADIAL COMPRESSIVE FORCE IS APPLIED TO THE CASE IN THE REGION OF SAID HEAD, DEFORMING SAID SKIRT INWARDLY AROUND SAID RIM SO THAT SAID EDGE EXTENDS TOWARD SAID HEAD, RELEASING SAID FORCE SO THAT SAID CASE EXPANDS OUTWARDLY AGAINST SAID EDGE AND SAID EDGE IS PARTIALLY IMBEDDED IN SAID CASE, AND DRIVING SAID EDGE FURTHER INTO SAID CASE WHILE SIMULTANEOUSLY SHAPING AND SIZING SAID METALLIC MEMBER ABOUT SAID RIM SO THAT SAID PLASTIC AT THE HEAD OUTWARDLY OVERLAPS AND COMPLETELY SURROUNDS SAID EDGE TO PREVENT CUTTING AND PEELING OF SAID BASE FROM SAID CASE.

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