In my area (south Florida) any weapon used in a crime (or in a suicide) will never see the light of day again once a department impounded it. We were even very, very careful about selling/disposing of surplus department inventory weapons (only through a large dealer). As a practical matter a weapon has a lifespan that will greatly exceed its first owner, and if properly cared for will work just fine 100 years later. Many chiefs of police are quite careful of disposing weapons since any reporter can trace one back to its source if they're willing to take the time and effort. With all the other things that can shorten the tenure of a chief, being anything other than very careful about weapons that the Department controls isn't the best idea. I'm sure many small departments do things differently but in urban areas that's pretty much been my experience....