Serial Number Restoration: Firearm

Serial numbers are placed on firearms during the manufacturing process and generally consist of a combination of letters and numbers or numbers alone. They are unique to an individual firearm, although there are instances where firearms from different manufacturers can have the same serial number. They provide a means by which law enforcement agencies can trace the origin and registered owner (if applicable) of a firearm. For this reason, they are often obliterated by criminals using methods such as filing, grinding, center-punching, over-stamping, drilling, or welding. There are a number of techniques that forensic firearms examiners use to restore obliterated markings and they fall into two broad categories, namely, nondestructive and destructive. The choice of restoration technique is determined by the type of metal involved, the process by which the serial number was marked on the firearms barrel or receiver, i.e., etching, casting, engraving, or stamping, and the method used to obliterate the serial number. Nondestructive restoration techniques include visual examination, often with the aid of a low-powered microscope, to establish whether sufficient detail exists to identify individual digits from the remaining portion of the serial number. Chalk or filtered light source examination can assist in enhancing these remaining digits. Destructive techniques include the use of magnetic particle and acid etching techniques. Chemical acid etching is the most common and successful technique currently in widespread use and can be used with or without heat. The techniques presented here can also be applied to the restoration of serial numbers in other situations such as on car chassis or engine blocks. Keywords: etching; electrical discharge machining; stamping; casting; engraving; filing; grinding; center-punching; over-stamping; milling; drilling; welding; nondestructive; destructive; magnetic particle; acid etching