Regardless of proof I think 3dram of black powder and 1 1/8 oz is too heavy a load for a gun of this age. I would think a limit of 2 3/4 dram BP and 1 oz would be a wiser load. Generally nitro powders generate twice pressure of black powders, but there is such a variance in burn rates and chamber pressures between the various nitro powders a little more research would be time well spent.