I am not sure that no other state has this policy; I thought CA did have this law. I know every Smith and Wesson gun comes with a fired casing for just such a purpose. I throw it in the trash.
Every time I run into one of these “ballistic fingerprinting” types (mostly educators), I suggest that why wouldn’t “automotive fingerprinting” also be a useful tool (computerize a copy of the tire treads on every new car)? A lot of times they get half way through the “but wear and tear . . .” when the light comes on and they shut up. Most of the others get a deer-in-the-headlights look at the utter stupidity of the proposal but can’t seem to make the correlation.