What are you going to be hunting? By "muzzle loader season" I will guess deer. For this I would try some 240 grain XTP's in a Harvester Black mag .452 sabot. You might also want to get a pack of the crushed rib sabots in case the regular harvesters are hard loading. You might also want to pick up a pack of 250 grain Shockwaves and see how they work.

Another option would be powerbelts. the 245 grain for deer should work just fine on 100 grains of Powder 2f.I would not push the rifle harder then that. You might also want to try some of the 348 grain pure lead powerbelts, again with 100 grains of powder or less. Although I think the 240 grain XTP's should work fine.

The problem with a rifle is while your friends might have the same rifle, what works in their rifles does not mean they will work in yours. All you can do is try different projectiles with different powder charges until you find on that works well for you. Then put it in the boiler room and let the projectile do the rest of the work.