Ed, Pressure is pressure. A gun does not care about the type of the powder. A gun is either safe to shoot, or is not. Have the wall thickness measured and if .025 or greater, shoot sane loads and be done with all the worrying. Sane, for a gun in proof, is 9,000 psi, closer to 7-8,000 is better and will do everything you need done. You could even go higher if you wanted but there are so many good loads 9,000 and under there is no reason to not jut pick one and be done with it. I even have loads in the 5,000psi range for some of my oldest doubles like a Westley Richards bar in wood hammer-gun. It is 150 plus years old and for that gun sane to me is 5,000. It is proofed for 2 3-4" loads and that would be well over 9,000 service pressure but single bite, bar in wood actions are not meant for too high a pressure for extended use. You might shoot a few hundred stouts loads but it soon would need tightening up the actions I fear. So low and slow instead of let the rip and we will fix her later.