I would not shot the power belts until I had checked them on a target. I shoot them and they fly good out of my gun. I would not worry about cleaning unitl after three shots no matter what bullet you shoot. There are some powder that burn much cleaner than others, such as powerdex and clearshot. What ever you choose, shoot a target first. All bullets are not created equal.
I agree with weekender. I shoot the wal-mart 260 and 240 grain. I can shoot good at three shots easily. Last Novemeber shot three does at 125 yards in 5 minutes. they kept dropping and didn't run so I just kept shooting. It was four of them and finally the last one ran before I could get her too. Just for the info where I hunt I am allowed to kill four at a time. I have a basic knight muzzle loader too and it does fine. Don't make things too complicated, just sight your gun in and have confidence, thats 95% of the game before the shot part. It don't matter how much you pay for your crap, if you can't hold a gun steady you will never make the first shot count, or the second, or third.
After a lousey hunt I let the old round rip... Cleaned up and then sent three powerbelts in quick succession down range using the same powder load... Nothing formal but the bullets went where the iron sights were laid as well as could be done from the shoulder... I dug one of them out of the back stop and uniformly flat at about 70 yards... Did a fourth shot and I upped from two to three pellets. Didn't hit any harder and seemed to pull left just a shade... Kind of same thing I had experienced with the sabot bullets...
least now you got a good idea of where they hit and you can put the smack down on some game without so many trips to the truck, MORE hinting time. Bring on the pics and tales.