AIRFORCE
I spoke to a guy back in my younger days in Miami. He was someone who went from town to town "correcting problems and mis understandings among the Sicilian population" He quipped "kinda of like a councilor of last resorts".
He was staying with a friends mother for a bit while he was in Miami. I met him sitting in his bathing suit at the kitchen table with 4 or 5 pistols disassembled. I asked what he was doing? His answer was "I am unsigning my work just in case"
I must have looks funny because he chuckled and explained.
Every barrel has a specific way they scratch a bullet as they go down the barrel. That is because some have 3 turns of one groove, others have 4 turns of 2 grooves. Each groove was cut into the steel of the barrel.
WHen the pistol is made in the US they send a spent bullet to the FBI along with the Pistols serial number.
What he was doing was reaching deep into the barrel with a slim pointed file and cutting a tiny mark into the barrel facing along the grooves at two different points. They were so small I had to use the magnifying glass to see them.
He mentioned that that little cut will change the pattern on the lead bullet just enough to prevent the 6 points required to match a retrieved bullet from a body or wall to a specific pistol.
He had he told me learned this from a friend who was a Jersey State Police Officer. He said they use it in case the perp, or a witness pointed them out. Their weapon would be taken, fired, and not match.
The guy told me his pistols were like old friends and he never ditched them since they would never leave him a trail.