Associating gunpowder and residues from commercial ammunition using compositional analysis

Area of Science:

• Forensic Science
• Analytical Chemistry
• Ballistics

Background:

• Traditional methods for associating gunshot residue (GSR) with ammunition have limitations.
• A novel approach involves analyzing the chemical composition of smokeless gunpowder additives.
• The propellant to stabilizer (P/S) ratio offers a quantitative measure for gunpowder characterization.

Purpose of the Study:

• To evaluate the efficacy of the P/S ratio and additive identity in associating handgun-fired organic gunshot residues (OGSR) with unfired gunpowder.
• To determine if this method can differentiate ammunition sources and link residues to specific cartridges.
• To assess the value of analyzing individual gunpowder and OGSR particles.

Main Methods:

• Qualitative identification and quantitative determination of additives in smokeless gunpowder.
• Calculation of the propellant to stabilizer (P/S) ratio for gunpowder and OGSR samples.
• Comparison of P/S values and additive profiles from commercial 38 caliber ammunition and test-fired residues.

Main Results:

• Gunpowder from four out of seven ammunition boxes was differentiated based on P/S ratio and additive composition.
• Visual inspection combined with chemical analysis allowed reliable differentiation of all seven ammunition boxes.
• Individual OGSR particles provided valuable data, and P/S measurement dispersity aided in associations and exclusions.

Conclusions:

• The P/S ratio, alongside qualitative additive analysis, is a robust method for associating OGSR with unfired gunpowder.
• Analyzing individual particles enhances the discriminatory power of this technique.
• Matching residue particle measurements to test-fired samples effectively accounts for compositional changes during firing.