tracing bullets

[bonsaimaster]

how can the police trace your gun to a crime with just the bullets, i heard its some scrachings that are different for every gun but how do they do it?

[Big Al1st]

They cannot trace the bullets to the gun unless they have had the gun at some time.

There are slight imperfections inside the gun barrel that leaves scratch marks on the bullet, also the rifling in the barrel leaves marks.This makes the bullet rotate. Like finger prints they vary from one gun to another but remain unique for that particular gun.
By firing a bullet out of the gun and comparing that bullet with the one used in a crime they can match the scratches. This is done with a special microscope where they can lay one bullet ontop of the second and thereby see the match.

It is quite a common procedure

[Mortartube]

Once the police have the suspect gun, they will fire a bullet out of it into a tank of water. This slows the bullet down so that it is undamaged and then any rifling marks etc can be compared with a bullet recovered from a crime scene.

[Grunty]

The tests are not done by the police, but by the Forensic Science Laboratories. They are completely independent of the police, and will not hesitate to give results opposite to the wishes of the police.

[stevie21]

Does nobody watch CSI?