According to Dr. Martin Fackler, a pioneer, essentially, in the field of ballistics, in reference to what forensic experts do on a daily basis, the term ballistics "refers to the science of the travel of a projectile in flight." The flight path of, say, a bullet, includes its "travel down the barrel, path through the air, and path through a target."
What seems to be an action that is rather quite simple—the firing of a gun—is, in fact, a complex set of circumstances that, when studied properly, can lead detectives down a road to finding, at the least, where a weapon was purchased and, at best, who purchased that said weapon. Each gun barrel leaves its signature mark on the bullets it fires—metal fingerprints, if you will.
Finding a bullet and matching it to a weapon can make and/or break a case.
What detectives investigating the brutal Ewell murders had found some solace in—if there was indeed any to be had within such a horrific murder scene—was the fact that they knew seven rounds had been fired inside the Ewell home, six of which they could account for. When—and if—they found the murder weapon, at least they had six metal fingerprints to work with.
A starting point.