BARREL HEATING IN HYPERVELOCITY POWDER GUNS

Abstract

When a gun fires, hot propellant grains and gas heat the barrel. The first phase of heating is the in–bore period (i.e., action time). During this period, the projectile travels down the barrel to the exit plane of the muzzle. The second phase of barrel heating is “blowdown.” When the projectile leaves, the hot high–velocity gas expands and accelerates, rushes out of the barrel, and sweeps forward over the projectile. The blowdown time is not a definite measurable quantity like the action time. The gas vents out of the barrel according to exponential decay formulas of gas dynamics. Mathematical models and results are provided for both phases of heating. For velocities over 1,000 m/s, radiation is the dominant mechanism. Conduction during blowdown is a large contributor.