Issue

One of the ammunition design constraints limiting the overall performance level of firearms is its barrel overheating, particularly for weapons firing high-energy ammunition at the muzzle at high firing rates.
Indeed, the operating principle of a firearm consists in propelling a projectile by the pressure of hot gases generated by the combustion of a propellant charge. This means that some of the thermal energy present in the propellant gases is lost through the heat transferred to the barrel’s inner wall, causing it to heat up significantly.Any shortcomings in the thermal management of a weapon result, at best, in a deterioration of the barrel’s service life (loss of accuracy due to the advance of the rifling in the barrel), and at worst, in a deterioration of the weapon’s safety (risk of cook-off, explosion of the barrel under mechanical stress during firing).

State of the Art

To compensate for the degradation of the barrel’s mechanical performance as it rises in temperature, a weapon designer must integrate passive or active cooling solutions (rapidly replaceable heavy barrel, cooling fins, heat sink, liquid cooling, etc.), or failing that, limit the power of usable ammunition or the acceptable firing rate.

Proposed solution

To reduce the thermal load on the barrel directly, without reducing the performance of the ammunition, the solution is based on the formation of a protective film on the inner wall of the barrel, as the projectile passes through, eliminated by the propellant gases. In this way, direct contact between the propellant gases and the barrel is delayed at least as long as it takes for the film to degrade, which means that the inner wall of the barrel is only subjected to significant heat transfer after a period of time that allows the temperature of the gases to fall as they expand in the barrel.

This protective film is formed by the transfer of material from a sabot surrounding the projectile, deposited on the barrel wall by erosion as the projectile passes through the barrel. To force and control the rate of degradation of the sabot, and thus control the thickness of the protective film, the barrel is tapered to reduce its internal diameter as the projectile progresses through the barrel, to a minimum determined by the diameter of the projectile.

To avoid excessive clogging of the barrel and facilitate evacuation of the protective film during each shot, the material used to manufacture the sabot must have at least one of the following properties:

A melting or sublimation temperature lower than the temperature reached by the combustion gases present in the conical section of the gun during firing.
A chemical composition complementary to that of the propellant gases, so that contact between the two is conducive to a chemical reaction whose products are in the gaseous state.
Contain a high proportion of propellant with a low combustion rate and relatively low combustion temperature.

Calculated performance

The implementation of this innovation makes it possible to achieve a level of performance in terms of projectile velocity at the muzzle of the barrel substantially higher than that obtained by a standard barrel of the same length, and potentially of the same order as that of an under-calibrated projectile using an aluminum sabot in a straight barrel with the initial diameter of the tapered barrel.