RE: 777 vs. Pyrodex (pellets)
You don't want to push powerbelts all that fast anyway. I am sure that you will have good luck with Triple Se7en or Pyrodex. The mistake a lot of people make with Triple Se7en over Pyrodex is they use too much. Loose Triple Se7en is 15% stronger then Pyrodex RS. So if you have a load that shoots well with 100 grains of Pyrodex and you switch to Triple Se7en and shoot 100 grains, you're pushing the projectile faster then your rifle might like. Yet if you would drop that T-7 load down to 85 grains or 90 grains, the results might be just as good or better.
Swab between shots and both powder work just fine.