Blake,
Be careful...I have the same gun and the specs show a max powder charge of 120 grains. Different than the muzzleloading rifle. Maybe with the 209 conversion kit (which I don't have) you can shoot 150 grains, I'm not sure about that. You're right though...even with 120 grains it kicks like a mule. If you shoot in the semi-dark you'll see that it throws a means streak of fire about 2-3 feet out the barrel as well. My best pattern comes with 120 grains of loose pyrodex and #5 Red Hot shot. Deadly to 40+ yards. Good luck!
NWBuck