source?

 

May not required everywhere and the link is hard to find. It is currently required for all ne gun purchases in NY and MD. On a federal level only guns involved ina crime are entered in an ATF ballistsic database. I bought 3 new guns this year and each came with two spent casings of which one was sent with my application to the LEOs. Cannot find a link of course anywhere in the MD government sites.

Here is a place to start the google search.
Ballistic DB

 

To a point. Swap out the barrel, firing pin, and if you're really paranoid extractor, and Mr. Finger Print goes away.

That's something you'd think would be entirely obvious to anyone with half a brain, but hey, no sense in not wasting perfectly good taxpayer money.

 

The firing pin doesnt make sense, metal on metal wears away. So wouldnt the "unique print" be mashed out of recognition after a while?

 

The pin is considerably harder than the primer. It's not going to change THAT much even with several thousand rounds. 'course, you could also just run a file over the end gently and completely change the "signature" of the pin.