>>8785097even if the bullet is intact, they can often only narrow it down enough to get a make and model
for example, they know it's a 9mm bullet, and that the gun had polygonal rifling, so they can narrow it down to a 9mm glock.
of course there are other 9mm handguns with polygonal rifling. Usually there are slight differences between the rifling patterns between brands though.
anyway, it's very rare that they can actually match to a particular gun. and all you would need to do is put a scratch or two on the inside of the barrel and it would ruin any attempt at a match.