Gunshot residue

Gunshot residue from a pistol shot

Gunshot residue (GSR), also known as cartridge discharge residue (CDR), gunfire residue (GFR), or firearm discharge residue (FDR), consists of all of the particles that are expelled from the muzzle of a gun following the discharge of a bullet. It is principally composed of burnt and unburnt particles from the explosive primer, the propellant (gunpowder), stabilisers and other additives.[1] The act of firing a bullet incites a highly pressurised, explosive reaction that is contained within the barrel of the firearm, which expels the bullet.[1] This can cause the bullet, the barrel, or the cartridge to become damaged, meaning gunshot residue may also include metallic particles from the cartridge casing, the bullet jacket, as well as any other dirt or residue contained within the barrel that could have become dislodged.

Law enforcement commonly use swabbing, adhesives and vacuums with very fine filters to collect GSR.[2] They commonly swab the web of the non-firing hand to look for gunshot residue if they are suspected to have discharged a firearm themselves or were in close contact with one at the time of discharge. Hair and clothing also accumulate GSR; typically a double-sided adhesive is used to sample areas that may have been exposed to such residue. It is also possible to use a swab moistened with 5% Nitric acid for collection.[2]

To determine if GSR is present in an area, presumptive tests, such as the modified Griess test and the sodium rhodizonate test, are performed. Any presumptive GSR samples are collected for confirmatory testing using instruments such as Scanning electron microscopy dispersive X-ray spectrometry (SEM-EDX) Flame or Graphite Furnace Atomic Absorption Spectrometry.[3] There are both inorganic and organic components in GSR. Organic GSR (OGSR) consists of organic compounds such as nitroglycerine.[2] Organic compounds can originate from the primer, propellants, lubricants or other additives used by manufacturers.[3] Analysis of OGSR is not done with the same instrumentation as stated above, instead techniques like Gas Chromatography-Mass Spectrometry are used.[3]

A graphic representation of the GSR left on a target when fired upon from varying ranges.
  1. ^ a b Warlow, Tom A. (2012). Firearms, the law, and forensic ballistics. International forensic science and investigation series (3rd ed.). United States of America: CRC Press. pp. 116–150, 248–368. ISBN 978-1-4398-1827-5.
  2. ^ a b c Bell, Suzanne (2006). Forensic chemistry (1st ed.). Upper Saddle River, N.J: Pearson Prentice Hall. pp. 441–457. ISBN 978-0-13-147835-0. OCLC 59756158.
  3. ^ a b c Wallace, James Smyth (2008). Chemical analysis of firearms, ammunition, and gunshot residue. International forensic science and investigation series. Boca Raton: CRC Press. ISBN 978-1-4200-6966-2. OCLC 190875984.