TC - I suspect it will take more than 100gr. of 2f or 1F and a 700gr. (1.6oz) bullet to beat 12,000PSI in that beast, and in the smaller rim size, 12,000psi should be a pussy-cat load. If you stay with black powder and groove diameter lead slugs in 2 1/2" cases, I dare say you could not strain the gun, no matter how much lead you send downrange heavy the load.

My 13 bore Husky (16 bore left barrel) shoots round balls at close range quite well - from it's straight rifling. Yes - I do wish it was twisted, but it isn't, so range for moose is restricted. It might be going moose/grouse hunting this Saturday. Lots of birds this year - hot dry summer (for here).