I came into possession of a WW2 Thompson SMG, M1A1 made by Savage Arms, while serving in Vietnam. Excellent short range defensive weapon, but a bit heavy to carry (especially with 8 or 10 mags) on patrols. When I DEROS'd out of Vietnam I gifted it to my successor, didn't think I could get away with stuffing it into my duffle bag for the flight home (I preferred going home to spending time in the stockade).
Left the Army, joined a police department that had 8 M1928 Thompsons in the armory. Somehow the bosses found out that I knew a little bit about the Thompson guns (which had been sitting around for a decade or two), so I ended up spending a week in the armory field-stripping, cleaning, test firing, re-cleaning, etc. All of the ammo was WW1 (1917-1918 headstamps) and WW2 (mostly steel-cased ball ammo in 20-round tear-open cardboard boxes).
About 1976 the department decided to trade in the Thompsons for new Colt AR-15 rifles. As I recall the dealer involved allowed $200 trade-in allowance per M1928 Thompson. No one wanted the ammo, so it was offered to officers for a nickel per round ($1.00 per 20-round box, $2.50 for the 50-round boxes from WW1). I stocked up and didn't have to worry about blasting ammo for several years. Still using some of the old WW1 brass for reloading range ammo these days (the steel cases aren't worth scrap value).
I have always enjoyed our national history. I never planned on being part of history, but somehow that appears to have happened.