Plastic Shot Shell And Base Wad

Abstract

A shot shell having a tubular casing made of hard polycarbonate plastic and terminating at its lower end at an integral base wall formed to provide an inwardly and axially projecting primer pocket is provided with a soft, yieldable polyethylene base wad having an axially extending central passage within which said primer pocket is received. The concave top surface of the base wad has a central aperture of smaller diameter than said axially extending passage, thereby defining an annular shoulder which abuts against the top of said primer pocket in sealing contact therewith. The aforesaid central aperture in the top of the base wad has a diameter at least equal to that of the inside of the primer pocket to thereby provide an unrestricted flash passage above a primer cap inserted into the primer pocket. An annular clearance space between the axial passage in the base wad and the tubular primer pocket in combination with a plurality of longitudinally spaced peripheral teeth on the base wad provide expansion room into which the resilient base wad may be compressed downwardly to provide a cushioning and shock absorbing effect that protects the lower end and base wall of the hard plastic casing from the pressures generated by the exploding propellant charge within the casing.

Description

BACKGROUND OF THE INVENTION

Numerous attempts have been made to manufacture a plastic shot shell casing which will not be ruptured or deformed by the pressures generated by the expanding gases of a propellant charge detonated within the casing. The problem becomes particularly acute when the shell casing is manufactured from hard and unyielding polycarbonate plastic. In order to avoid damage to the head or base end of the shell casing, pressure-absorbing base wads of various designs have been installed within the lower end of the casing adjacent the base wall. Prior art base wad designs have been deficient to the extent that they provide neither an adequate cushioning effect nor a proper seal around the primer cap. If the base wad does not seal tightly around the primer, expanding gases from the detonated powder charge will escape rearwardly with a resultant wasteful dissipation of energy and possible damage to the base of the shell casing. The problem of distorting or splitting the shell casing at its base end becomes particularly acute where the entire casing, including its base or head, is formed as an integral unit from hard polycarbonate, and no reinforcing metal head is place over the base of the casing. Unlike linear polyethylene, polycarbonate is very hard and unyielding, and thus is quite susceptible to failure under the pressures generated by an exploding charge within the shell casing. The novel polycarbonate casing and base wad design of this invention has been designed to overcome the aforesaid difficulties.

BRIEF SUMMARY OF THE INVENTION

Having in mind the aforesaid problems associated with the manufacture and use of shot shells having hard plastic casings, I have designed a polycarbonate shell casing and plastic base wad which cooperate in such a way as to prevent the transmission of excessive gas pressure to the lower end of the casing and to tightly contain the detonated gases within the desired space above the primer cap.

These basic objectives are realized by utilizing a soft, yieldable polyethylene base wad of annular shape which seats snugly around a tubular primer pocket which is formed integrally with the casing base wall and projects from the center thereof upwardly into the casing. The polyethylene material of the base wad is sufficiently yieldable and resilient that it will compress and deform under the pressures generated by an exploding charge so as to cushion the hard plastic casing and distribute the shock waves evenly thereto.

As a particularly beneficial feature of my invention, I enhance the cushioning effect of the polyethylene base wad by providing an annular clearance space between the inside, tubular wall of the base wad and the primer pocket into which the polyethylene material may flow as it is subjected to detonation pressures. Also, axially spaced, peripheral teeth on the base wad lend it additional compressability and shock absorbing capacity.

A further beneficial aspect of my invention resides in the provision of an annular shoulder in the top wall of the base wad which abuts against the top of the primer pocket in sealing contact therewith to prevent the rearward flow of detonated gases around the primer cap. This sealing shoulder, in combination with the sealing effect obtained from tight engagement of the aforesaid peripheral teeth of the base wad with the inside surface of the plastic casing insures that no gases will leak rearwardly to the base wall.

These and other objects and advantages of my invention will become readily apparent as the following description is read in conjunction with the accompanying drawings wherein like reference numerals have been used to designate like elements throughout the several views.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevation view, partially in section, showing the improved plastic shot shell and base wad of my invention;

FIG. 2 is a bottom perspective view of my improved base wad;

FIG. 3 is a horizontal section view of the lower end of the shot shell taken along lines 3-3 of FIG. 1; and

FIG. 4 is a fragmentary section view of the lower end of the shot shell showing on an enlarged scale the form which the yieldable base wad will assume upon detonation of the propellant charge.

In FIG. 1 of the drawings I have shown a shot shell having an all plastic outer casing 1 with an integral base wall 2. An annular flange 3 on the periphery of base wall 2 serves as a contact element for an ejection mechanism in a shotgun. Casing 1 may be rolled over at its upper end 4 and provided with a top closure member, not shown. Projecting axially into casing 1 from the center of base wall 2 and formed integrally therewith is a tubular projection 6 which serves as a primer pocket within which primer cap 8 is inserted. Tubular casing 1 is preferably molded from hard, impact-resistant polycarbonate, with base wall 2 and primer pocket 6 being formed integrally therewith.

Disposed within casing 1 is a shot cup 10 which contains a shot charge 12 and is shown, for illustrative purpose only, as being part of a unitary overpowder wad, spacer, and shot cup device generally indicated by reference numeral 14. Device 14 is also preferably formed from a molded plastic such as polyethylene and includes a downwardly depending overpowder wad 16. Cooperating with overpowder wad 16 to confine a powder charge 18 therebetween is a base wad 20.

As may be noted with reference to FIGS. 2 and 3 as well as FIG. 1 base wad 20 is of annular shape and has an elongated central passage 22 extending axially thereof. As is indicated in FIG. 2, the annular bottom 24 of base wad 20 is substantially planar, this shape being given to bottom wall 24 n order to permit it to conform to and seat against planar base wall 2 of casing 1 in the manner shown in FIG. 1. With base wad 20 seated in the bottom of tubular casing 1, tubular primer pocket projection 6 will be received within axial passage 22. As may be noted with respect to FIG. 1, the tubular wall forming axial passage 22 of base wad 20 is of slightly greater diameter than the outside of tubular projection 6, thereby providing an annular clearance space therebetween. This clearance space operates to improve the compressability of base wad 20 as will be understood from the description of the operation of base wad 20 hereinafter set forth. Upper wall 26 of base wad 20 has a concave shape shown most clearly in FIGS. 1 and 3. At the center of concave wall 26 is a circular aperture 28 which is of somewhat smaller diameter than axial passage 22. By virtue of this construction an annular shoulder 30 is formed at the upper end of base wad 20. Shoulder 30, which appears most clearly in FIG. 2, abuts against the top of tubular primer pocket 6 and assists in sealing gases within propellant chamber 18 in a manner hereinafter explained. Circular aperture 28 has a diameter at least as great as the inside diameter of primer pocket 6 so as to thereby insure an unrestricted flash passage through which flames from detonated primer cap 8 may pass upwardly into propellant chamber 18. To further improve the compressability and sealing function of base wad 20, it is formed with a plurality of axially spaced sealing rings 32 extending around its periphery. Sealing teeth or rings 32 fit snugly against the inside wall of casing 1, and being flexible and yieldable may be forced into tight engagement with casing 1 under the influence of the exploding propellant charge.

The gas pressure generated by the detonation of propellant charge 18 will compress and deform polyethylene base wad 20 from the shape shown in FIG. 1 to that illustrated on an enlarged scale in FIG. 4. Teethlike sealing rings 32 will be forced downwardly and pressed together to thereby provide a cushioning and shock absorbing effect as top, concave wall 26 of base wad 20 is urged downwardly to the position shown in FIG. 4. Due to its concave shape, top wall 26 will also receive and transmit force radially outwardly with the result that sealing rings 32 will be forced into tight contact with the inside surface of casing 1. An effective seal will thus be provided along the lower, inside surface of casing 1 to prevent expanding gases from flowing downwardly between base wad 20 and casing 1 towards base wall 2. The downward pressure exerted by the expanding gases on detonation will also force annular shoulder 30 into tight, sealing engagement with the top end of tubular primer pocket 6. The tight seal thereby provided between shoulder 30 and primer pocket 6 prevents the downward leakage of combustion gases along the outside wall of primer pocket 6. Because relatively soft and deformable polyethylene shoulder 30 is seating against plastic primer pocket 6, a particularly effective and improved seal is obtained at this point as compared to that which would be achieved if shoulder 30 were abutting against the top of metallic primer cap 8. The cushioning and shock absorbing capability of polyethylene base wad 20 is further enchanced by providing the annular clearance space shown in FIG. 1 between tubular wall 22 and the outside surface of primer pocket 6. The downward pressure acting on base wad 20 at the time of detonation will not only force sealing rings 32 downwardly but will also compress the annular body of base wad 20 to such an extent that the polyethylene material thereof will flow into the annular clearance space around primer pocket 6. Since bottom wall 24 of base wad 20 is normally seated against the inside surface of casing base wall 2, the compression of annular base wad 20 in a downward direction is limited and it is thus forced to deform radially inwardly, thus filling the annular clearance space around primer pocket 6 in the manner shown in FIG. 4. The plastic-to-plastic contact of base wad inner wall 22 along the whole length of the outside wall of primer pocket 6 provides a very good seal to further insure against the downward leakage of exploding gases. Polyethylene base wad 20, being resilient as well as yieldable and deformable, will return to its normal shape after the shot shell in which it is used has been fired.

It will thus be seen that yieldable, polyethylene base wad 20 of the particular configuration shown and described cooperates with the lower end of polycarbonate casing 1 and plastic primer pocket 6 in a unique way to very effectively shield the lower end of casing 1 and its integral base wall 2 from the potentially damaging effects of the exploding propellant charge. The sealing and shock absorbing functions of polyethylene base wad 20 in cooperation with plastic primer pocket 6 are especially important and critical when using a hard, unyielding polycarbonate casing 1 which is particularly susceptible to deformation and rupture and which is not protected by a tubular metal head over its base end.

Claims

I claim:

1. A shot shell comprising:

a tubular casing made entirely of hard, polycarbonate plastic, said casing terminating at its lower end at an integral base wall having a peripheral flange of larger diameter than said casing;

a tubular primer pocket extending axially into said casing from the center of said base wall, said primer pocket being formed integrally with said base wall;

an annular base wad having an elongated central passage within which said tubular primer pocket is received and a bottom surface conforming to the inside surface of said base wall and seated there against in surrounding relation to said primer pocket, said base wad being made from relatively soft, yieldable and resilient plastic an having an annular shoulder at the center thereof resting upon the top of said tubular pocket in sealing contact therewith, and the inside diameter of said shoulder being at least as great as the inside diameter of said tubular pocket;

a powder charge within said casing on top of said base wad; and

a plurality of continuous resilient teeth closely spaced longitudinally along said base wad and extending circumferentially about its periphery, said teeth being arranged in sealing contact with the inside surface of said casing.

2. A shot shell as defined in claim 1 wherein:

the inside wall surface of said elongated central passage of said base wad is disposed radially outwardly from the outside surface of said tubular primer pocket for a substantial portion of the length thereof so as to define an elongated, annular clearance space therebetween into which the plastic material of said base wad may flow as it is compressed by the pressure generated by said powder charge exploding within said casing.