Issue

Production methods for ammunition intended for military use (particularly for small-caliber weapons) have not evolved significantly since the standardization of 5.56 x 45 mm ammunition in the mid-1960s.
This is due to the close relationship between the case production method and the performance obtained, such as maximum admissible pressure, or the mechanical strength of the case during the extraction of the fired case from the chamber.
However, production methods in other industries have evolved considerably, so much so that the processes used to manufacture ammunition with monolithic metal casings have been replaced by others that consume fewer resources, energy and, above all, manpower. As a result, the industries needed to produce ammunition using these processes and located in Western countries have lost a lot in competitiveness, leading to relocation and a loss of sovereignty over ammunition supply chains.

State of the Art

The production of ammunition case for small arms (5.56 mm and 7.62 mm calibers, but also .50) has remained static since the late 1960s, and is itself the result of particularly conservative approaches in technological terms. Indeed, the manufacturing process involves the use of mechanical presses to produce the case (as well as the projectile jacket) by cold-forging, interspersed with cleaning operations and heat treatments to avoid the creation of stresses that would cause tearing, either during manufacture, or when the ammunition is used.
As demonstrated by developments in the field of medium and large-caliber weapons, the non-reversible modernization of weapons and ammunition systems, when it involves a change of caliber, is the ideal circumstance for drastic update in the ammunition production methods.
In this respect, the implementation of the innovation protected by patent FR 22 04909 of separation between the chamber and the barrel can be considered sufficiently complex on an industrial scale to justify a complete overhaul of ammunition production methods. This is all the more true since, in order to maximize the duration of secondary thrust, it is necessary to maximize propellant retention in the chamber during firing, by using powder grains with dimensions greater than the cross-section of the neck.

Proposed Solution

To enable propellant filling of the combustion chamber of a munition implementing the innovation protected by patent FR 22 04909, it is useful to make the case in several parts, which are assembled after loading with propellant powder. In order to guarantee the solidity of the case body assembly, particularly when it is removed after firing, a third part can be used to lock the assembly together, preventing the base and insert, in which the nozzle separating the combustion chamber from the barrel, from being disassembled.

The ideal material for the base of the cartridge case is lacquered steel, to take advantage of its increased strength compared with that of the brass usually used in older cartridges, in order to maximize chamber pressure in complete safety. The insert in which the nozzle is formed, enabling propulsion gases to pass through the gun at supersonic velocity, can be made from substantially lighter materials, such as certain plastics, provided they are resistant to thermal stress. For this purpose, a material such as ceramic can be used, either in the form of a composite with ceramic in the form of glass microspheres embedded in a polymer matrix, or in the form of a surface treatment on the surfaces exposed to the propulsion gases.

Two architectures are preferred:
An architecture with a long base and a short insert, where the combustion chamber is formed in the base. In this configuration, the chamber is closed by crimping the base onto the insert. An external locking device can be fitted.
An architecture with a long insert and a short base, where the combustion chamber is formed in the insert. In this configuration, it is preferable to internally lock the assembly by means of a spacer
passing through the channel between the insert and the combustion chamber.