I examined the rifle a little further. A loose .224 bullet will only enter the muzzle to the cantelure, so it probably is a .22 of some kind. The barrel is originally a .22 of some kind. It isn't a reline job. The case rim is identical to a .22 Hornet, but the Hornet case will only enter the chamber about half way. I'm thinking some kind of .22 centerfire rook cartridge. Maybe I can have a gunsmith rechamber it to .22 K-Hornet. It would be nice to know what it is though, before I have someone take to it with a reamer.