Once again, I'll reinterate the basic rules of muzzleloading.
CONSISTENCY, CONSISTENCY, CONSISTENCY.
If you want accuracy, you must achieve absolute consistency. The means same amount of powder, same amount of force when seating the bullet, same cleanliness of the barrel for each shot, etc.
1. Loose the pellets. They are notoriously inconsistent. Plus, you can't fine tune your load. Sometimes as little as 5 or 10 grns plus or minus will make the difference between a 2" group and a 1" group.
2. Use a bullet with a good BC. My favorite are Hornady SSTs which are the same as the T/C shockwaves. There are others that shoot just as flat. Some people have good results with Powerbelts but others (me included) can't get them to shoot for crap.
3. Be patient when sighting in. I remove the breech plug and clean the bore with EVERY shot while target shooting. That is because a real hunting shot will always be on a clean barrel.
4. Learn to clean it properly. The stuff you use to clean your regular guns will not work on a muzzleloader. Black powder (and substitutes) are water soluable not oil soluable. Therefore, you have to either use the stuff made for BP or just juse ordinary warm water with some dish soap (it's cheaper and works just as well).
5. Don't try to go for a max load. If you could see a graph of the extra velocity you gain when you go over 100 grns and compare that against the extra recoil and muzzle blast, you'd see that you are running into the law of diminishing returns. Plus, you generally start to loose accuracy. Unless you are trying to shoot elk, 100 grn +- is plenty.