Ed, to say shoot the gun with black powder is stupid. Pressure is pressure, no matter what type of powder is used. 6,000 psi with black is 6,000 psi with nitro. Both are 6,000 psi. Perhaps the peak is reached an inch further down the barrel. Perhaps it differs a few hundred psi someplace. But either a barrel is safe to shoot with any type powder or not. To say use only black powder is just as dumb as say to not use high brass shells in a gun. The height of brass does not tell you pressure.