also you have to remember most of the "forensic" tools leo has are after the fact after you've been captured when they're trying to make a legal burden. when you're halfway across the country and they have no leads no amount of residue or rifling analysis is going to get them any closer to you. they have stuff like the stingray for actually tracking you but that's another topic for another time. it's not going to be residue or casings or rifling that do you in unless you're already in custody, all the bluster about that stuff is only to dissuade people from even trying anything.
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