I have found a old inteteresting cartridge


I found an old cartridge with zero information on it other then the letter U stamped on it and it appears to be a rim fire. Anyways I was wondering if someone could help me figure out what this is.


As there are likely to be perhaps a few hundred different
rimfires with a U stamped on it. A whole bunch more information is needed.
Photos, accurate measurements in 1/1000 of an inch & such would be a start


? Well ?