I spoke with one seasoned hunter and he uses machined copper slugs with a diameter .01" less than his bore diameter with a blunt nose tip. He has also used tungsten carbide round balls although very expensive. He said the tungsten carbide goes right through a buffalo. He said penetration is not a problem with either the solid copper slug or the tungsten carbide round ball.

I would think solid round ball .01" smaller in diameter than your bore would work very well. And using daryl's past experience supporting the accuracy of round balls, I think solid coppers may be quite lethal and accurate. I wonder if anyone else has solids experience or have some different conclusions.