There is a fellow up the road in Greensboro that developed a muzzle loader a few year back that uses smokeless powder, last name of Bell...You guys may have heard of him...His testing grounds is eastern NC and his bullet of choice is a 300gr Hornady .452 XTP...He has killed a few hundred with this bullet...I figure that's good enough...

I don't believe you'll push that or any other XTP too fast with black powder or a sub...