Experiments using a light gas gun to investigate the impact melting of gunshot residue analogues

In this set of experiments, the versatility of the University of Kent's light gas gun was utilised to obtain a selection of corroborative data regarding the formation and impact of metallic gunshot residues onto high purity silicon wafers. The results from the two experiments are presented. The first experiment investigated how the formation of metallic residues varied as gunshot residue analogues traversed through air under a range of pressures from 0.056 millibar (5.6 Pa) to 1 bar (100 kPa), using solely the energy released during primer ignition; the second involved firing a metallic powder mix of pre-determined composition (via a split-sabot) under vacuum at two velocities- 500 ms-1 and 2000 ms-1. This ensured that there was no ignition or heating of the powders, unlike the first experiment, and so the morphology of the particles collected would be solely due to impact. The residues on the substrates were then analysed using a cold Field Emission Gun Scanning Electron Microscope (FEG) and Energy Dispersive X-ray (EDX) detector. By separating the ignition process of the primers from the residue impacts, it allows for a closer look into the formation of these particles and helps determine whether their varied morphologies are due to the heating caused during the activation and combustion of the primer or whether its due to impact melting. This information can aid in the understanding of metallic particle formation in different pressure environments and give insight into the physical state of firearm residues when they impact a surface. Hydrocode modelling was also incorporated to corroborate the results observed during these experiments and gave results which mimicked the experimental data.