Current trends in firearms and ammunition are toward lighter and easier to carry firearms and ammunition. These include the use of various plastics in the manufacture of firearms and some large, well-known manufacturers are experimenting with the development of caseless ammunition (combustible cartridge cases and primers) which, if viable, will involve major design changes in the mechanism of firearms.
The disadvantages of caseless ammunition include the very high cost of totally new weapons and ammunition manufacturing systems, relative fragility and sensitivity of the ammunition, and difficulties with weapon maintenance and repair in the field.
Advantages of caseless ammunition include space and weight saving, a cost saving over brass-cased ammunition, a material saving (copper is a critical material during wartime), and a higher cyclic rate of fire made possible because the extraction and ejection cycle of conventional firearms is no longer necessary (about 2,200 rounds per minute is possible). The higher rate of fire improves the chance of hitting the target on firing a three-round burst.
The concept of caseless ammunition is not a recent one as such ammunition, for use in breech-loading firearms, has been in circulation for well over 100 years. The concept was experimented with by different countries at various times, but with only limited success. Typical compositions consisted of nitrocellulose (12.6% nitrogen) 65%, kraft paper 15%, resin 20%, and diphenyl-amine (added) 1%. The German firm of Heckler & Koch has relatively recently solved many of the problems associated with caseless ammunition and produced a rifle, the HKGH, to fire 4.73 x 33 mm caliber caseless ammunition.
Caseless ammunition has no cartridge case to serve as a heat sink and barrier between the propellant and the hot chamber walls. The problem of "cook-off," that is, the heat rather than the firing pin causing the cartridge to discharge, has always been a major disadvantage with caseless ammunition. Heckler & Koch has solved this problem by the use of a propellant that contains no nitrocellulose but is based on materials more commonly associated with explosives than with propellants. The composition is a commercial secret but the new propellant has an ignition temperature about 100 K greater than nitrocellulose-based propellants.98,99
Figure 13.1 illustrates a cross-sectional view of the 4.73 x 33 mm H&K caseless ammunition. It is rumored that Heckler & Koch have since abandoned the project.
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