outdoorsmen,
First off - YES on the 777 powder. You' ll like it. It' s very consistent and VERY Powerful - 15 to 20% hotter than any other powder, so you' ll have to reduce any Pyrodex or Black Powder loads you want to duplicate.
As far as bullets go - there are many options. The Barnes work well and it' s hard to get too far off with the Knight bullets. The Hornady XTP bullets work well too for a more economical price. But for the absolute best performing & most accurate muzzleloading bullets - go visit these guys:
http://www.prbullet.com/
Call ' em up and talk to Cecil - the guy is the absolute wizard of muzzleloading. Tell him what you are shooting & what game/target you' re after and he can tell you the exact bullet & load you need. I' ve had exceptional results with their Extreme HPs and QT polymer-tipped bullets - drop dead kills and penny-sized groups at 50meters!
One word of advice on bullets - don' t be afraid to shoot the heavier bullets (especially if you bought a .50cal rifle). Small, light bullets offer impressive muzzle velocities - but rarely offer target-class accuracy. These fast-twisted, wide-landed barrels really seem to need longer bullets for stable flight and good accuracy. My Knight USAK (.50cal) just refuses to shoot what I consider to be good groups with any bullet under 300gr (" good" groups being 2" or less at 100yds).
Good luck - that is one sweet rifle you got!!