well id see if you can find a slugging kit and slug the barrel (soft lead slug pounded down the barrel so that you can determine the actual diameter). some barrels vary alot from what the company intended them to be. also the chamber may have to be reamed to proper dimensions. i know we arent supposed to do this but you could try asking the people over at
www.sixgunner.com on their forums they may know more since it is a somewhat obscure cartridge. good luck