The Effects of :Lacquered Ammunition on the Toolmark Transfer Process
thesisposted on 01.05.2020, 00:00 by Nicole Groshon
When a firearm is discharged, the bullet and cartridge case acquire unique microscopic markings called ‘toolmarks’. Firearm forensics involves comparing two objects with similar toolmarks. These comparisons typically involve the bullets or cartridge cases found at a crime scene to ammunition that was test-fired with the suspected weapon. Historically, the primer faces of fired cartridge cases have been examined using a comparison light microscope and entered into a database. In recent years, agencies and laboratories have been transitioning to two and three-dimensional imaging to aid in faster comparisons with the help of automated search software programs. The database assigns a match score for the cases and the examiner makes a final comparison of the evidence and test fired ammunition to determine if there is a true match. One troublesome feature firearms examiners may encounter is the lacquer that is commonly used to seal the primer of cartridges. The purpose of the sealant is to prevent moisture from making contact with the gunpowder inside the cartridge, which would render it useless. So far, little research has been done to test the effects of lacquer on the transfer toolmark process on fired ammunition. Whether an examiner prefers using the comparison light microscope or virtual imaging, the lacquer may need to be removed at some point during the examination as it tends to chip and flake off in patches thus completely changing the topography of the surfaces compared. There has been concern, however, that the cleaning process may destroy some of the individual characteristics that are also necessary for comparison. In this study we aim to examine several different firearms to determine if lacquer affects the toolmark transfer process.