Ballistics is the study of projectiles in motion.  In the world of forensic science bullets are matched to the gun they were fired from by both class and individual characteristics.  The groves, lands and striations left from the barrel are the marks used to compare a suspect bullet to a test bullet.  Casings are matched by the mark left from the firing pin as well as scratches known as breech block marks.  Below are some examples we use in class.