No way to be sure without experimenting enough Try different grain bullets. Start low on powder charge, say 50 or 60 grains. Work your way up in 10 grain incraments until you find the most accurate load for your gun. Remember- magnum loads almost always have higher deviation, produce huge recoil and minimum increase in velocity. Muzzleloaders aren't made to shoot as fast as your favorite modern rifle. They do shoot heavy enough projectiles that they easily kill what you shoot(obvious variables aside). Speed doesn't matter if you can't shoot well.
Remember the old 45-70 buffalo killers? That's .45 cal and 70 grains black powder.
