Analysis of Polymer-Coated Bullets Using Spectroscopic Methods

Polymer-coated bullets have gained popularity because they can reduce the user’s exposure to heavy metals in the ammunition. The synthetic jacket, which surrounds the lead core, is advantageous because it prevents metal-on-metal contact between the bullet and the bore. A challenge for firearms identification is that polymer-coated bullets do not retain unique markings that can be used to identify the gun, the way standard metal-coated bullets do. However, metal-coated bullets will result in a similar challenge if the bullet is too deformed once it is recovered. Another issue is that the composition of the polymer coating was never disclosed by the manufacturer, so we do not know if it is harmful to the user. The goal of this research was to determine the composition of 9mm Luger Federal Syntech Total Synthetic Jacketed (TSJ) and 9mm Luger Federal Syntech Defense bullets by studying the solubility, melting point, and molecular vibrations of the polymer coating. Additionally, impact marks on wood and steel were examined for traces of polymer residues. Infrared spectroscopy indicated that the polymer on the of 9mm Luger TSJ ammunition was most consistent with polyethylene glycol terephthalate. The polymer on the 9mm Luger Federal Syntech Defense was most consistent with dimethyl iso phthalate. Furthermore, the polymer on the 9mm TSJ bullets had a much higher melting point than the polymer on the 9mm Syntech Defense bullets. Finally, 15 of the 22 wood samples had visible polymer residues, while all 4 of the steel samples had no visible polymer residues