I tried this a couple of years ago but nobody would tell me what it was. So here goes agian, one more time.
22 caliber that I got from an old shooter who is now in heaven. Appears ordinary until you look at the base. Heavily indented and what appears to be a BB, or something like that, swadged into the base. Also appears to be a seperate narrow band at the very base that has been swadged also, maybe to hold the “BB” in place?
All in all, very unusual.