The Sources of Lead in Gunshot Residue
 

By: Lucien C. Haag, Forensic Science Services, Carefree AZ

Key Words: lead, gunshot residue, bullet wipe, ‘pick-up”, “gas-cutting”, firearms discharge products, persistence

ABSTRACT

The presence of lead in gunshot residues is typically and easily detected with the sodium rhodizonate reagent either applied directly to certain evidence items or through transfer techniques. Lead is also one of the three elements sought and associated with gunshot residue in atomic absorption and SEM techniques. A number of sources of lead are present in contemporary small arms ammunition but this is in a state of rapid change with the increasing appearance of lead and heavy metal-free primer compositions. Traditional primer mixes have contained the impact sensitive explosive lead styphnate. This continues to be the case with most common centerfire ammunition. Some of the lead from this source emerges from the muzzle of the gun upon discharge, some is deposited in the bore of the firearm and some is frequently deposited on the exterior surface of the bullet during its journey through the gun barrel. Lead bullets and the lead rubbed and eroded from them during the discharge process are obvious sources of lead residues. These residues may emerge from a firearm at the moment of discharge in the form of particulates or vaporous material- both of which respond to the sodium rhodizonate reagent and can be recognized as such by the appearance of the resultant color complex with this reagent. Thermal erosion is also a source of lead when open-based, full metal jacketed bullets with lead cores are discharged from a firearm. Total metal jacketed bullets or otherwise lead-free bullets may acquire lead on their bearing surface from direct contact with lead residues in the bore of the firearm or from lead-containing primer mixes. This lead will be detectable in the “bullet wipe” around the margins of bullet holes. The isolation and independent study of these sources and their persistence with the advent of new, lead-free ammunition can provide considerable insight and understanding as to the source(s) of lead in gunshot residue testing in actual casework.