The Transfer and Persistence of Propellant Residue Originating from the Discharge of a Firearm

Abstract

Firearms examiners are frequently asked to provide an estimate on the distance between the muzzle of the firearm and the target, at the time the shot was fired. To achieve this, the firearm residue pattern around the bullet entry hole is examined and compared with examples prepared at various distances, using the same firearm and ammunition combination. Difficulties can arise in this distance estimation if certain circumstances have caused a possible change to the residue pattern, between the time of the shot being fired and the laboratory examination taking place. Changes in the residue pattern might be expected if the victim has moved, bled significantly, or if they had died outside and a significant rainfall occurred before the scene environment could be protected. Currently, uncertainties exist around the amount of change that might be expected and there is a limited amount of research to provide information, supporting the examiner’s interpretation. This research project is aimed at filling the knowledge gap around the persistence of propellant particles on different surfaces after being subjected to different influencing factors. Two different commonly encountered calibres were chosen (.22LR and 9 mm Luger) to provide caseworkers with research examples from which to draw upon. Different propellant types within each calibre were also selected to study the influence of different morphologies on the persistence. Overall results show differences in propellant shape, barrel length and distance affecting the level of transfer to the surface. Propellant shape and fabric type influenced the degree of propellant loss during the persistence experiment. Blood significantly reduced the quantities of residues seen, while rain and movement slightly reduced the quantities. The speed of the movement and the length of time also influenced the degree of propellant loss. Future research is recommended to confirm the theories established in this study and to further investigate the effects.