Firearms examination is a discipline of forensic science which has as its primary concern to determine if a cartridge case, bullet or other ammunition component was fired in a specific firearm. This is actually a form of toolmark examination where the firearm, because it is made of material harder than the ammunition components, acts as a tool to leave impressed or striated marks on the various ammunition components that come into contact with the firearm.
To complete this, examiners test firearms to determine if they are functioning properly and obtain test fires by discharging the weapon into a large water tank. This provides exemplars from the firearm that may be compared to evidence from the scene. The examination is carried out using a specialized comparison microscope.
The same concept is used when performing toolmark examinations, where a toolmark is left at the scene and a suspected tool is collected. Test toolmarks are produced using softer metals (lead, copper, aluminum) and compared to toolmarks collected at the scene.
Serial number restorations can be attempted because when a serial number is stamped into a piece of metal, the molecular structure of the metal changes forever. Even if the surface is ground away or filed down, the structure of the metal molecules that remain may have a “memory” of the original stamp. By applying different restoration methods, including acid etching and magnetic techniques, the original stamp can often times be at least partially restored.
The section has a firearms reference library of around 1700 firearms that were scheduled for destruction. These guns provide the section with the opportunity to obtain parts for submitted guns that are broken or otherwise inoperative. It also provides the examiner a way to study the workings of a gun prior to handling a gun submitted as evidence, or serve as serial number structure reference and location if an evidence weapon’s number has been obliterated.
Gunshot residue and distance determination is the examination of clothing and other items for the presence of gunshot residue or shot patterns in an attempt to determine muzzle-to-object distance.