Electrical Pulse Generated Upon Discharging a Firearm and Its Implication for Gunshot Residue Analysis

Ammunition primers consisting of a mixture of lead styphnate, barium nitrate, and antimony (III) sulfide, upon deflagration, lead to the formation of inorganic gunshot residue (GSR). The cations, from their predeflagration form, undergo reduction reactions during burning to form the classic spheroidal, micron-sized particles indicative of GSR. However, the rapidly changing pressure and temperature of the reaction zone implies that the reactions cannot go to completion. In this study, we use a conductivity detector to show that GSR produces an electrical pulse which corroborates the incomplete redox chemistry. We find that the shape of some GSR formed in an electric field also suggests its nonneutral character. Tantalizingly, the formation of GSR might be a result of Coulombic repulsion shattering the molten droplets in to smaller spheroids. Lastly, we suggest that deposition or transfer of GSR could be influenced by static electricity, an area which should be further studied.