Unidentified, Very Old .51 .Cal Rimmed Cartridge
My neighbor asked me to identify this strange old cartridge, (see photo) which he found in upstate NY many years ago. The lead bullet is about .51 cal. It is hard to measure with calipers, because the bullet is lumpy, corroded and out-of-round. The bullet weighs about 338 gn., a monster. The cartridge overall length is 1.8". The cartridge has at least two other strange characteristics: First, as can barely be seen in the photo, it has no primer, but has a pinhole opening. Next, the rim on the brass casing is enormous.
Can you identify this cartridge for me?