Selling it for a profit would just open a whole new can of worms for this guy.
Lol, then as they attack use the new one
He should keep it hidden and give it a good coat of oil every few months, and then pass it down to his heirs.
Somebody 50 years from now may pay big, big money for that gun. Like maybe enough to set somebody up for a couple lifetimes.
Or not. Who knows anymore?