You still have to deal with the forcing cone and the tapering of the barrel. It really would depend on the sabot holding the ball. Seeing how I have never seen it offered, I doubt many of us has pressure measureing equipment to find out if its safe or not. Steel would not have near the density to do much anyway. Now Tungten, maybe. You could always get some heat treated balls. Might shatter on impact. Maybe if you gave use some idea of its use? Wouldn't be good on deer. A copper solid would penetrate better I believe.