Comperatative analysis of primer and gunshot residues using scanning electron microscopy

Gunshot residues (GSR) are the particles that arise during the firing of a firearm. When a bullet is discharged, both the primer and propellant ignite, resulting in the simultaneous release of combustion byproducts. These residues encompass various components, including unburned and partially burned propellant powder, particles from the ammunition primer, smoke, lubricants, grease, and metals from the cartridge and gun itself. The organic compounds found in GSR primarily originate from unburned and partially burned gunpowder particles, as well as propellants and firearm lubricants, manifesting as hydrocarbons. Inorganic residues such as nitrates, nitrites, and metallic particles mainly come from the primers, propellant, shell or core, and the gun barrel. It is important to note that primary GSR particles are formed from the primer before the propellant is ignited, while secondary GSR particles are produced as the propellant burns and the bullet is propelled out of the firearm. Analyzing GSR can aid forensic investigations by determining whether a firearm has been discharged and providing evidence to link a suspect to a shooting incident. Although GSR analysis using scanning electron microscopy/energy dispersive X-ray spectrometry (SEM/EDS) has been extensively studied, no literature has been reported on SEM/EDS GSR analysis of 7 different brands of bullets and capsules alone. In the current study, three different brands of bullets were close shot to the paper and the acetate paper directly and by removing the bullet core. GSR particles were collected on a stub containing adhesive/conductive tape. EDS images were collected along with SEM secondary electron (SE) and backscattered electron (BSE) images. SEM/SE images were used to determine the morphology of the GSR particles, SEM/BSE images were used to determine the composition of the GSR particles containing heavy metals, and the compositions of the particles were determined by SEM/EDS maps and analysis results. More particles were collected from primer firings. It was observed that particles of primer firings did not have a certain morphology. However the GSR particles of bullets were smaller and spherical due to the gunpowder effect. Inorganic analysis and morphological evaluations of GSR samples with SEM/SE, SEM/BSE and SEM/EDS can be considered as a more ideal approach for GSR analysis.