I won this Frank Wesson at a local auction and it looks like a fun shooter but I'm not sure of its actual chambering, they were made in both .30 rf and .32rf. I suspect .32 since they were more common and have found that the bore will accept a .301" pin gauge and the chamber will accept a .321" pin gauge. I've not been able to find cartridge specs for these older rounds so that's all I have. I have been looking at the .32rf thread and considering the .27 cal nail gun blanks and modified cases but haven't made it all the way through yet. I do wonder about the strength of this tiny little pistol though. It is a neat little gun and it has a near perfect bore.