Back in the late 60's I was in an NRA youth shooting group that met at the indoor range in the basement of the Police Department. One day after practice a couple of officers showed up with a Thompson. They had 50 round drum mags and the whole kit in a hard case.

We asked if we could stay to watch. We got a few "I don't know.."'s then I said we'd clean up the brass for them. SOLD! Man that was impressive to a bunch of kids at the time.

I found out later they had six of them when I wandered into their armory one day.