Sounds like your powder and projectile selection was a good indication of what you can expect your gun to do.
The different point of impact for bullets weighing significantly different isn't surprising, Things like barrel "whip", recoil, etc figure into that, and you may find them hitting quite differently - especially at 100 yds or beyond.
Powerbelts - there's a couple of different opinions on them. Some have good success with them on animals and some have had dismal failures in their ability to penetrate heavy bone and still get into the "boiler room". I've decided to NOT try them on game, but go with a bullet like an XTP or other that has a more consistent track record.
Keep reading posts and you'll get a lot of info.
Welcome to the sport of muzzleloading!
IM jaybe
