Gunshot Residue (GSR) Analysis

Contributed by Faye Springer

Gunshot residue analysis refers to the chemical analysis of particulate materials resulting from the discharge of a cartridge in a firearm. In its broadest definition, the analysis of GSR includes the identification or characterization of gunpowder, products of gunpowder combustion, primer mixture components, metallic residues from the projectile and cartridge case, and possibly chemical residues from the firearm itself. However, more commonly, gunshot residue (GSR) analysis refers to the analysis of residue on the hands of a shooter or other surfaces in the vicinity of a discharging firearm. Most of these analyses specifically target residues resulting from the detonation of the primer mixture inside the primer cup of a round of ammunition, or cartridge.

GSR is typically collected from the hands of a suspected shooter, or from other objects, on adhesive lifts intended for examination by a scanning electron microscope with an energy dispersive spectrometer (SEM/EDS). Gunshot residue using SEM/EDS is based on original research published by G. M. Wolton of Aerospace Corporation in 1977. 1, 2, 3

Subsequently, forensic laboratories started applying this technology to case work. In 1994, a standardized method for the analysis of GSR by SEM/EDS was published by the American Society for Testing and Materials (ASTM) as Standard E1588 4.

In 2005, a scientific working group on gunshot residue (SWGGSR) was formed with representatives from the international forensic GSR community. The goal of this group was to the develop guidelines for forensic GSR analyses and guidelines for reporting practices. It also provides a platform for exchanging information concerning current issues in GSR. This group’s publications can be found on their website at www.swggsr.org/‎.

GSR particles are most commonly characterized by their shape and chemical composition. Because the particles are formed by the cooling of the molten particles created during the discharge of a cartridge, they tend to be micron or submicron sized particles and somewhat spherical or rounded in appearance. The most common primer mixture consists of lead styphnate as an initiating explosive, barium nitrate as an oxidizer, and antimony sulfide as a fuel. Therefore, the presence of these elements in a spherical or somewhat rounded particle is defined as a characteristic gunshot residue particle.

With lead free primers or ammunition becoming more popular, other chemical components may be present in primer mixtures. The Guide for Primer Gunshot Residue Analysis by Scanning Electron Microscopy/Energy Dispersive X-Ray Spectrometry 11-29-114 published on the SWGGSR website has more information on residue from these types of ammunition.

The presence of characteristic GSR particles on a subject’s hand typically leads to the conclusion that this person:

  • discharged a firearm,
  • was near a firearm when it was discharged,
  • or handled a firearm or another object contaminated with gunshot primer residue.

    • The lack of GSR particles on the hands of a subject typically means that:

  • the subject did not discharge a firearm,
  • the weapon or ammunition used in this case does not deposit detectable GSR based on current technology,
  • or previously existing GSR deposits on the person’s hands were removed by washing or other mechanical means over time.

    • Gunshot residue analysis can be expected to change as materials used in the manufacture of ammunition and firearms changes. In addition, newer generation instrumentation that offers increased sensitivity, specificity, and speed can be expected to influence current procedures and techniques used in the detection of GSR.

    References:

    1. Wolten, G. M., Nesbitt, R. S., Calloway, A. R. Loper, G. L., and Jones, P. F., Particle Analysis for the Detection of Gunshot Residue, I: Scanning Electron Microscopy/Energy Dispersive X-ray Characterization of Hand Deposits from Firing. Journal of Forensic Sciences (1979): 409-422.

    2. Wolten, G. M., Nesbitt, R. S., Calloway, A. R. Loper, G. L., and Jones, P. F., Particle Analysis for the Detection of Gunshot Residue II: Occupational and Environmental Particles. Journal of Forensic Sciences (1979): 423-430.

    3. Wolten, G. M., Nesbitt, R. S., Calloway, A. R. Loper, G. L., and Jones, P. F., Particle Analysis for the Detection of Gunshot Residue III: Case Record. Journal of Forensic Sciences (1979): 864-869.

    4. ASTM Standard E1588-10e1, Standard Guide for Gunshot Residue Analysis by Scanning Electron Microscopy/ Energy Dispersive X-ray Spectrometry.

    5. Guide for Primer Gunshot Residue Analysis by Scanning Electron Microscopy/Energy Dispersive X-Ray Spectrometry 11-29-11, www.swggsr.org/‎.