I have the same rifle, other then mine is right handed and flintlock. I find it likes Heavy Conicals and heavy sabot loads. I have been shooting the 450 grain UC Short Mags out of mine with about 70 grains of Schuetzen black powder. Also I shoot some 424 grain LEE Mold 405-458 bullets in a sabot. Again, 70 grains seems to work nice. The thing of a large bullet is, it don't take a lot of powder to make them lethal.

Also for fun I was shooting roundball out of it. And with 50 grains of powder it will really do a fairly good job out to 50 yards. I have not done any real long range shooting with the rifle yet.