Alright so I was out digging today and found an old Brenneke 12 guage slug. Never found one before but I'd imagine they usually don't have a screw in them? The screw makes it look like a top and it spins like one also. Anyone seen one before?
I found some info on this. The screw is actually part of the slug and not an addition to it. It held the wad and nitro card on the back. Should be about 30-40 years old.