Firearms examiners identify gun shot residue (GSR) by detecting primer residue particles. Most residue expelled from a gun consists of burned, unburned, or partially burned propellant which contains metal particulates such as lead, copper, brass, or nickel from the jacketing material. The firing pin of a gun contacts the back of the cartridge, initiating the primer, which ignites the propellant, forcing the bullet down the barrel. Heat and pressure vaporize the metals from the primer which escape from the weapon. The vaporized metals cool and condense forming tiny metal containing particles. GSR particles are easily removed from surfaces and are typically collected with adhesive lifts. Analysis is performed with a scanning electron microscope and energy dispersive spectrometer (SEM-EDS). Characteristics of GSR are the identification of lead styphnate (initiating explosive), barium nitrate (oxidizer), and antimony sulfide (fuel). The morphology of the condensed GSR is spheroid indicating it was molten. The particle must relate to other particles in the sample in order to determine it comes from GSR.
Reference: The Current Status of GSR Examinations, Michael Trimpe, FBI Law Enforcement Bulletin, May 2011, p24 -32.
NCFS Research:
- Source identification of metals in GSR and priming cup post-fire.
- Determine if there is a correlation between post-fire GSR, the metal plating, and cartridge case for both traditional and lead-free bullets.
- Developing a single devise for field detection of organic and inorganic GSR.
For more information contact Dr. Candice Bridge.