Cartridge Case and Cartridge Arrangement and Method

Still other objects and attendant advantages will become apparent from a reading of the following detailed description of a preferred physical embodiment constructed according to the invention, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a longitudinal section view of a preferred embodiment of a cartridge case and cartridge employing a metal base and glass-fiber reinforced plastic sleeve according to the invention, showing such in a cartridge chamber preparatory to firing.

FIG. 2 is a fragmentary view of the cartridge and chamber, illustrating schematically the action of the various parts during firing and resultant propellant gas pressurization.

FIG. 3 is a cross-sectional view of the cartridge case during the ignition phase of the propellant. This cross-sectional view illustrates the effect of the longitudinal forces on the chevron-type mating surfaces between the metal case base and the plastic case shell wall.

FIG. 4 is an enlarged fragmentary section view of the chevron joint, schematically illustrating the venting and friction relieving action of the vent holes along a portion of the joint during firing.

FIG. 5 is an enlarged fragmentary section view of the plastic sleeve portion of the chevron joint showing the zone of interface frictional loading and sealing during firing and the friction-relieving action effected by gases passing through the friction-reducing vent holes.

FIG. 6 is a fragmentary section view of a substantially less desirable modification according to another aspect of the invention in which the sleeve overlaps the metal base, in which the vent holes are formed.

Referring now in detail to the Figures of the drawings, in the illustrative embodiment cartridge 11 has a metal-plastic cartridge case formed of a metal base 13, a suitable metal being steel, brass, nickel, etc. and a plastic sleeve, suitable plastic materials being glass-reinforced or other fiber-reinforced nylon, polycarbonate, acetal resin or the like.

A projectile 21 of suitable desired configuration is suitably secured in the cartridge, and a conventional or other desired main propellant charge 18 is ignitable by a conventional percussive or other desired primer 14 which is provided for igniting the main propellant charge, the illustrative example including an intermediate black power charge which may have a frangible cover 16a thereon.

In the illustrative embodiment the nose end of the projectile 21 is carried in a steel sleeve 27 within the bore 27b of which it rides during exit from the case 13, 15. Sleeve 27 has a radially extending end flange 27f which is pressed forwardly against the rear face of the weapon barrel 45 upon firing of the cartridge 11, and an annular obturating case seal 29 is provided to seal the propellant gases during the firing action. The nose end of the illustrative projectile is provided with a bore-riding nylon sleeve 25 and a multiple ring seal 23 which wedges along the tapered projectile surface to effect a seal with the bore 27b initially and subsequently with the barrel bore 45b.

The cartridge 11 is shown a chambered in a firing chamber 43c formed in a firing chamber block 43, and removably secured in place by a pawl 31, with a breech block 41 through which a suitable firing pin 51 moves to percussively engage and fire the primer 14 and the propellant powder charges 16, 18.

The cartridge 11 as seated in the firing chamber 43c may or may not have an initial head space gap of significant size at the front and/or rear end of the cartridge 11 between the cartridge and either or both of the barrel rear shoulder 45s and the breech block 41, and/or the breech block structure may itself permit a significantly large head space charge to be effected, and thereby effectively elongating the firing chamber, during firing and under the pressures of the propellant gases acting on the opposite end sections 13 and 15, 27 of the projectile. As a result the metal base 13 and plastic sleeve 15 are moved in opposite directions by the combined amount of any initial head space and the increase in head space through elongation of the firing chamber 43c under the pressure exerted during firing of the propellant charges 16, 18 to propel the projectile from the cartridge case and along the barrel bore 45b.

To this end it is desirable to provide a joint between the metal base 13 and the plastic sleeve which will not only withstand handling loads and acceleration loads during firing, but also will enable the relative longitudinal expansion movement between the metal base 13 and nylon sleeve 15 during firing without rupture or separation, while still effecting a sealed joint both prior to and during firing.

As an illustration of the overall head space which may be required to be accommodated, in one chamber of approximately 13.25 inches length a head space change of approximately 0.120 inch has been encountered.

To this end, it is important to minimize the incidence of failure at the metal/plastic sleeve joint under these practical operating conditions where such may occur, and the present invention is directed to accomplish this object and purpose.

The metal base 13 is joined to the plastic sleeve 15 through an annular chevron joint which provides both good handling and acceleration load strength while providing an effective obturating gas seal during firing. In addition the joint enables frictional relief or reduction along a substantial extent of its length during firing to thereby enable the joint to accommodate the relative frictional sliding movement between the base 13 and sleeve 15 for head space accommodation and thereby minimizing the otherwise substantial likelihood of separation failure at the joint.

The chevron joint is formed by two annular interfacing intermating complementary annular step-like chevron surfaces 13ac and 15ac formed respectively on the forwardly facing rim lip 13a of the metal base 13 and the rear end surface 15a of the plastic sleeve 15. The chevron surfaces 13ac and 15ac are also generally tapered, and the plastic chevron section 15ac is the radially inboard one of the two sections, thereby enabling the plastic section to be obturated and into sealing relation with the stronger less yielding metal band therearound as formed by the inwardly facing chevron section 13ac of the metal base rim. In the assembled condition prior to firing the joint is mechanically stable and forms a secure mechanical interlocking connection. In addition, as above noted, the tapered inner chevron section 15ac will be obturated radially outwardly into continuing sealing contact with the metal base chevron section 13ac under the forces of the propellant gas pressures during firing of the cartridge 11 and propulsion of the projectile 21.

However, due to the problem of the requirements for accommodating initial and/or increase of head space in the firing chamber upon firing of the cartridge, the chevron joint has very substantial longitudinal tensile stresses exerted thereon, which desirably are accommodated by permitting longitudinal slippage along the chevron joint intermating surfaces. With the chevron joint as simply above-described the interface friction along the entirety of the length of the chevron surfaces 13ac and 15ac is so great as to seriously approach or exceed the strength of plastic materials, including those reinforced with glass or other suitable fibers. This problem is minimized by providing a plurality of radial vent holes 17 in the zone of the chevron surface 15ac spaced sufficiently away from the chevron zone 15ac3 as to enable it to maintain an obturating seal with the corresponding chevron surface 13ac3 of the metal base chevron section 13ac, while enabling pressure-equalizing passage of the pressurized propellant gases through the vent holes 17 to thereby relieve the friction forces along the adjoining chevron surface sections 13ac1, 13ac2 and 15ac1, 15ac2. The total effect is to materially reduce the friction and mechanical surface area, and thereby reduce the resistive forces opposing a sliding expansion of the chevron joint during firing, and to thus enable a substantially greater assurance of maintaining not only an effective gas seal at the joint but also to maintain the structural integrity and reduce the likelihood of failure of the case at this zone.

The action of the vented chevron joint 13ac, 15ac is shown schematically in enlarged form in FIG. 4, the venting separation action being exaggerated for clarity of illustration. FIG. 5 illustrates the zone of resultant obturating seating 15ac1 and 15ac2. The illustration in FIG. 4 shows schematically the radial deformation at 15ad of the plastic sleeve 15 which results from obturating deformation of the sleeve 15 outwardly against the metal base in the zone of sealing chevron zones 13ac3, 15ac3, 15ac3. Likewise, FIG. 4 schematically shows the resultant elongation movement positioning of the base 13 and sleeve 15 joint sections 13ac, 15ac, resulting in a gap into which a small radial obturating convex deformation of the sleeve 15 may occur, as shown.

It will thus be appreciated that a metal/plastic cartridge case and cartridge construction is provided which not only provides a good interface joint seal which has strength for withstanding handling and acceleration loads, but also has provision for automatically reducing the joint interlock resistive action during firing, and this minimizes and materially reduces the likelihood of joint failure during firing, where large head space expansion is involved.

FIG. 6 illustrates a modification of the invention which, while technically feasible, is substantially less desirable than the previously illustrated and described embodiment of FIGS. 1-5. In FIG. 6, the base 113 and sleeve 115 are joined together with the sleeve outside and the base inside at the chevron slip-vented interface joint, formed respectively by base chevron section 113a and sleeve chevron section 115a. Radially extending holes 117 are formed in base 113, which together with chevron surfaces 113ac and 115ac serve to enable automatic reduction of joint interlock resistive action during firing, in a manner similar to the reduction of joint interlock resistive action, at the vented chevron interlocking joint of the preferred embodiment of FIGS. 1-5.

While the invention has been specifically illustrated and described with reference to both an illustrative and preferred embodiment and a modification embodiment, it will be apparent that various modifications and improvements may be made without departing from the scope or spirit of the invention. Such modifications, although substantially less desirable, include reversal of the slip-vented interface joint such as in the modification of FIG. 6, reversal of the materials, and use of other materials. These mentioned alternative modifications offer substantially less advantages and, to a varying extent (varying with the individual modification) less reliability than is provided by the preferred embodiment. Accordingly, it is to be understood that the invention is not to be limited by the particular illustrative embodiment, but only by the scope of the particular illustrative embodiment, but only by the scope of the appended claims.