A 2" rifle at 100 yards is a good shooter. The broken petals is no reason for concern, especially in the Shockwaves. The 6-8" groups sound about normal if the 100 yard group is two inches. Granted it could be tighter, but 200 yards is a long way for a muzzleloader. Good shooting.

What you might want to try is different bullets. Some Barnes Expanders, Parker Ballistic Extremes, Nosler, some of them might do a better job for you out of a Knight rifle.

Actually I think you have a good rifle going, and the more you experiment the better it will get. Nice shooting.