dog1: You are talking apples and oranges. You ask about powder difference then mention pellets. Similar animals, but very different in actual use.
3 pyrodex and T-7 pellets are about equal. Loose powder is 'nuther animal.
Here's some GENERAL observations on loose powder.
Pyrodex is roughly equavilent to musket grade Elephant brand black.
Goex is about 5% stronger ( for want of a better word) than Elephant, Scheutzen is about equal to Goex, but alleged to be cleaner burning, Swiss is about 20% stronger than Elephant, much cleaner burning, but is a true SPORTING grade powder, so use 20% LESS AND go up one grain size, T-7 is on par with Swiss in power, but is a differant animal as T-7 is not black powder.
Swiss is a real good coice in small bore muzzle laoders. In larger bores, .50 and up, switch from 2fg Goex or Elephant or T-7 and use 1.5 fg Swiss and cut the load 20%