Years ago, my father worked/ran a scrape yard with a shredder and about once every 12 to 18 months the ATF, FBI and the local police department would put up with boxes of handguns, rifles and knifes to put through the shredder.
The biggest part that came out was about the size of a half-dollar. Most of
the guns were junk but I have seen some quality guns. I would guess the most expensive was a Colt Gold Cup.