How big is it at the muzzle? If it were me I'd want at least .550 at the muzzle and enough meat around the chamber to be safe. You might talk to Allen at Clearwater Reboring, he'll be able to do the work and can advise you if it's safe or not. You can find him here: allen@deltagunshop.com
I just had him do a rolling block barrel for me, and he's very good to work with.
