How do they use ballistics tests to match the bullets to the criminal's gun?

Question

We see this all the time in movies and TV, but how does it really work?

And how do they know that it is exactly the criminal's gun? There are many copies of every single gun out there. Is every single gun, no matter if it's the same model or whatever, unique in some way?

Answer 1

The inside of a barrel of a gun has individual markings that are unique to it. Those markings are transferred to the bullet as it passes through. A person only needs to match the markings do determine if the gun was the same.

Every single gun is different, no matter if they are the same model or not.

Once they have a weapon in custody, they test fire the weapon and use the test round to match to the original casing recovered.

Answer 2

If the round is recovered, they view it under a microscope and record the "striations" they find on it... or a unique pattern of markings from the inside of the barrel. When they have a suspect and a gun, they shoot a "comparison" round from the suspect gun and compare the markings. If they match, that's the gun.

Answer 3

If my understanding is correct the barrel of the gun has a finger print and every time a bullet is fired from that gun it ingrains its foot print on the bullet. So all they have to do is match it up.

Answer 4

Each barrel of a gun has its own markings , like fingerprints, yeah, there must be thousands of similar guns, but the markings are each different. Except with shotguns of course.

Answer 5

one way is to match the spent round up with a round fired out of the suspect weapon, they can match up the rifelings, because they all are slightly different, and also they can match up the mark of the firing pin makes on the casing.

Answer 6

They look at the marks the firing pin leaves on the casing.