Energy dispersive X-ray analysis of bullets commonly encountered in Taiwan

The detection and identification of gunshot residues (GSR) may provide valuable investigative and forensic information to crimes involved with firearms discharge. These residues are composed of propellant residues, as well as metal components derived from primer mixtures, bullet, and barrel. During firing, GSR is mainly deposited on the shooter and the target. If the range of shot is sufficiently close, residues called GSR I will directly deposit on the target around the bullet hole. A small amount of residues called GSR II carried by the bullet will deposit on the abrasion ring of the entrance. Bullets contribute a substantial amount of metal ingredients to the target GSR. Better understanding of bullet structure and major elemental composition would be valuable to forensic scientists for their analysis work and interpretation of results. Bullets extracted from 35 kinds of commonly encountered cartridges were subjected to elemental analysis using scanning electron microscopy/ energy dispersive X-ray analysis (SEM/EDX). The results indicate that lead bullets and cores of full metal jacketed (FMJ) bullets are usually composed of Pb-Sb alloy. Pure lead is often used for bullets and lead cores as well. The other projectile materials found in this work are Pb-Sb-Sn alloy and steel. A coating of different elemental composition was detected on some bullets. The coating elements detected on the external surface of lead bullets include Al, Ca, Cu, F, P, Sn, and Zn. Bullet jackets are usually made of Cu-Zn alloy or pure copper with an exception of steel jacket. The jackets are sometimes plated with nickel. The data concerning the elemental composition of bullets can be used to decide the methods to be employed for the identification of bullet hole and the determination of firing distance.