Total guess, but... Navy 1 pounder 37x137mm case? Armor piercing... Age and era? Could be any. William
"Much that once was, is lost. For none now live who remember it."
Thanks Steve and William, I guess its a mystery....had it for some time, it came with another 20mm round and some .50 Cal shells that I paid 8 bucks for.
Nice shell bro!