Associating gunpowder and residues from commercial ammunition using compositional analysis

Qualitatively identifying and quantitatively determining the additives in smokeless gunpowder to calculate a numerical propellant to stabilizer (P/S) ratio is a new approach to associate handgun-fired organic gunshot residues (OGSR) with unfired powder. In past work, the P/S values of handgun OGSR and cartridges loaded with known gunpowders were evaluated. In this study, gunpowder and residue samples were obtained from seven boxes of commercial 38 caliber ammunition with the goals of associating cartridges within a box and matching residues to unfired powders, based on the P/S value and the qualitative identity of the additives. Gunpowder samples from four of the seven boxes of ammunition could be easily differentiated. When visual comparisons of the cartridge powders were considered in addition to composition, powder samples from all seven boxes of ammunition could be reliably differentiated. Handgun OGSR was also collected and evaluated in bulk as well as for individual particles. In some cases, residues could be reliably differentiated based on P/S and additive identity. It was instructive to evaluate the composition of individual unfired gunpowder and OGSR particles. We determined that both the numerical centroid and dispersity of the P/S measurements provide information for associations and exclusions. Associating measurements from residue particles with those of residue samples collected from a test firing of the same weapon and ammunition appears to be a useful approach to account for any changes in composition that occur during the firing process.