My Green Mountain Barrel also likes strong loads. I shoot 110 grains of Goex 2fin my .58 caliber with a .570 round ball and a .017 patch. In my .54 caliber I shoot 100 grains of Goex 3f and a .530 ball and patch. In my .50 caliber Green Mountains I shoot 90 grains of Goex 3f and a .490 patched ball. And in the .50 caliber 1:28 twist, today I was shooting 120 grains of Pyrodex RS and a 200 grains Hornady XTP. Accuracy with them is excellent. The GMB just seems to like a stiff charge.

That is some nice shooting there... way to slide them in there.