The only references I have found for pressures indicate a 12ga from the blackpowder era probably didn't exceed 8000psi. Unfortunately, it is hard to say how they were measuring pressure then, probably with LUP. If I were certain my damascus barrels were sound, and could get a pressure value for the ammo you are citing indicating it is less than 8000psi I would likely shoot it. If you handload the pressures can be brought well below 8000psi. It is the pressure and the weight of the shot charges which have changed over the years. You could also submit it for Nitro Proof.