Determination of the Muzzle-to-Target Distance in Shooting Cases Using Inductively Coupled Plasma – Optical Emission Analysis of Barium, Lead, and Antimony

Between 2015 and 2023 firearm-related deaths almost doubled in the U.S., increasing discussions concerning gun control measurements. Gun regulations vary between states. States like Mississippi have not only relaxed gun control laws but also the highest firearm-related deaths. Research involving inorganic gunshot residue (IGSR) typically focuses on the shooter end rather than the target material. This work aimed to create a mathematical relationship between the concentration of metals on target materials and the muzzle-to-target distance for the estimation of shooting distance. Cloth samples containing IGSRs were obtained by shooting a Remington UMC 9mm Luger ammunition from a Smith & Wesson M&P9 Shield semi-automatic pistol in a controlled indoor environment at varying distances. The IGSR was extracted from samples using an acid digestion procedure and analyzed using Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) to quantify barium, lead, and antimony. A mathematical model was developed for the interpretation of barium, lead, and antimony in both ammunitions analyzed. Polynomial regression was employed as an exploratory tool to visualize the non-linear relationship between IGSR concentration and shooting distance within the experimental range studied. This research provides evidence that the relationship between muzzle-to-target distance and the concentration of metal on the target material not only exists but is polynomial. The results demonstrate a measurable non-linear relationship between inorganic gunshot residue deposition and shooting distance. While additional validation across different firearms, ammunition types, and target materials is required, these findings provide evidence supporting the future development of quantitative approaches for shooting distance estimation.