Robert: IMO the .50 is in the transitional area where either FFg or FFFg works well.
Some claim the FFFg burns cleaner although I have never seen much difference in a .50 .
As a general rule "they" say use the FFFg in the .45 or under and the FFg in a .50 or larger.
I think if your shooting 85 or 95 grain hunting loads it would be better to go with the FFg as it will keep the pressures down a little. The other powder I shoot (in precussion guns) is Pyrodex. Never had any problems with the RS in my .45, .50, .54, or .58 and it doesn't foul the bore as much as Black powder.
I havent shot the triple 7 so I can't judge it. At least one of the "new" non fouling powders are ascorbic acid based (seemed to cause more headaches than it cured) and I haven't seen much written about any of the newer ones by Actual Shooters (hey any of you out there want to put in some comments about quickness of ignition, consistent velocities, repeated accuracy, Price?).
I tried Grand Canyon? once. A fellow muzzle loader got it for free "to test" and was so pleased with it he gave it all to me. After firing it I was so pleased with it I took it out back and set it afire to get rid of it.
Edit: OK, bite my lip. I went over to the In Line area and they discuss 777 there. I didn't see anything on prices though. I think it was 777 I saw at a gun shop but when I saw that the price was over $20/pound I lost all interest.