This may not be the right place to post this, my apologies if it's not. I was sifting through some old ammo that Granny always said Pa brought back from WW2 and came across something interesting (actually a few somethings, but I digress); I found what appears to a copper cased .30 rimfire cartridge! The case is just a shade over 3/4 of an inch long. It has a round nose lead bullet. The only marking is a large U stamped in the center of the case head. It is a rimmed case. Anyone have any ideas? All I can find is that they've been out of production since 1917. Any help is appreciated.