I use 3f in all my rifles, and that includes 62 smoothbore.
Typical day at the range shooting my 45 cal T/C Hawken, I usually fire around 20 times or so, and never clean between shots.3f will burn cleaner, faster, and you use about 10% less per load.
My 45 likes 60 gr 3f or 70 gr 2f. If using Pyrodex, I use P (pistol) powder instead of Pyrodex RS The equivalent of 2f black powder. Pyrodex works well, but the Goex is better.I'm not familiar with 777.