The Technique
Rifling marks, down the barrel of a gun.
The theory behind ballistics analysis is that the manufacture and use of a firearm produces unique tool marks inside the barrel, which are then transferred to each bullet fired from that gun. Forensic examiners measure bullet size to determine caliber, then check the direction of rifling marks and the degree of twist to narrow down the gun's manufacturer. To match a specific firearm to a bullet, investigators test-fire the weapon with a new slug and compare both bullets under a microscope, looking for identical striations. Also they check flight trajectory and the angle thta the projectile went in to the body. Investigators can also check computer databases that suggest potential matches.