[nightdriver]

"When a bullet is fired, it is scratched with unique markings, or "fingerprints," as it passes through the gun's barrel. The law requires gun manufacturers to test-fire handguns and send a spent shell casing from each gun sold in Maryland to the state police."

So what do they catalog, the bullet or the shell casing?

[neverdem]

So what do they catalog, the bullet or the shell casing?

I could be wrong, but I think they do both. I'm pretty sure the ATF's IBIS system does both. Here's a link.

[Cobra64]

So what do they catalog, the bullet or the shell casing?

That is what I was wondering. Then I realized these jerks do not know the difference.

I'd send 'em a spent primer.

[Yo-Yo]

The bullet rifling marks are cataloged, and the shell casing firing pin and extraction marks are cataloged.

Sometimes at a shooting all one has to go on are spent shell casings, and extractor marks and/or firing pin marks have been enough to provide a match to a particular weapon.

But again, the marks left when new are almost never close to the marks left after years of use. Ballistics matching are usually only effective when there are few rounds between the test round and the crime scene round.