: Microscopic flaws in the manufacturing process or wear and tear from use create a "signature" unique to that specific barrel. 2. Impression Marks (on the casing)
: When the gun fires, the casing is forced backward against the breech face, transferring its texture to the metal. bullet fingerprinting
As a bullet travels through a gun barrel, it is gripped by —spiral grooves machined into the metal to make the projectile spin for stability. : Microscopic flaws in the manufacturing process or
: The pin strikes the primer at the back of the casing, leaving a unique indentation. bullet fingerprinting
: The hooks and pins that pull the spent casing out and toss it away leave distinct scratches on the rim. The Technology of Tracking