Triboelectric charge variability in firearm particulates and projectiles

In this paper, we investigate the variability of dynamic triboelectric charging of both particulate emissions (smoke, unburned propellant and other debris) and projectiles launched from a 9 mm Beretta pistol. We measured charge transients both at the weapon muzzle and at a location 10 m downrange using cylindrical charge sensors to characterize the charge associated with the muzzle blast and that of the projectile. We derive an analytical expression for the time-domain voltage response of cylindrical charge sensors, and use it to quantify the charge present on the projectiles. Our results indicate that the magnitude and polarity of charge present on a given projectile depends strongly on the ammunition type, even if the primer and propellant chemistries are identical. Projectiles, on average, carry a charge opposite in polarity to that of the particulates present in the muzzle blast. We hypothesize that the relative motion of the gas-solids flow in the annulus between the barrel and the projectile leads to charge transfer between the particulates and the projectile, resulting in the case of oppositely charged projectiles and particulates.