Gunshot residue

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), and vaporized lead. The act of firing a bullet incites a very violent explosive reaction that is contained within the barrel of the gun, which can cause the bullet, the barrel, or the cartridge to become chipped. Meaning gunshot residue may also included metal fragments from the cartridge casing, the bullets jacket, as well as any other dirt or residue contained within the barrel that could have become dislodged. Law enforcement investigators will swab people's hands 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 discharge. In order to figure out if GSR is present in an area, chemical tests, such as the Modified Griess test and the sodium rhodizonate test are performed. Any GSR samples are collected by swabbing with 5% nitric acid solution and onto a SEM disk for a confirmatory test with scanning electron microscopy. Scanning electron microscopy dispersive X-ray spectrometry (SEM-EDX) is used to determine the presence of gunshot residue as a confirmatory test. There are both inorganic and organic components in GSR. Organic GSR primarily consists of compounds classified as explosives or additives based on their chemical composition and they are analyzed by analytical techniques. Before the use of the scanning electron microscope, hot paraffin wax was used to take a cast of the suspect’s hand. The cast was then sprayed with a reagent giving a coloration with nitro-compounds from the partially burnt and unburnt propellant particles. This approach, introduced in 1933 by Teodoro Gonzalez of the Mexico City Police Laboratory, is called dermal nitrate or paraffin test and is no longer used in casework.