Originally Posted by joshua99ta
this just kind of bumfuzzles me how supposedly they can prove that a bullet came from a certain barrel when there are thousands a day produced.
I mean I know the chances of somebody else could have a rifle with the same tooling and it be in the same place arent likely but I doubt mass produced barrels have different toolings for every barrel.
They certainly look different, even to the eye in a borescope. Also, the usage histories of the rifles will be different probably beginning with the first shot. Different break in, different cleaning, different bullets, plus the initial differences just in chambering tolerances (which are pretty wide in factory guns) and there is essentially zero chance the scratches on the bullets or cases will be identical.
Trust me on this, based on years of looking for root cause failures in silicon chips it is really hard to make things as gross as a barrel identical at a microscopic level on purpose, never mind by accident.