I would NOT use Hodgdon 777 in that fine, old original revolver.
It's tricky stuff, subject to pressure jumps when compressed too heavily.
Hodgdon itself notes in its section on loading black powder cartridges:
Loading density should be 100% with light compression not to exceed .100inch. Testing has shown that Triple Seven will perform best when the bullet just touches the powder. Allow no airspace between the base of the bullet and the powder. Do not reduce loads by means of filler wads or inert filler material such as Grits, Dacron or Grex. Do not heavily compress powder charges. The use of filler wads, inert fillers or heavy compression may cause a dangerous situation, which could cause injury and/or death to the shooter, bystanders or damage property.
Now, while the above specifies cartridges, a wise muzzleloading shooter will also heed this advice though he doesn't use brass cartridges. Clearly, Hodgdon is warning that too much compression can cause problems.
Here's what Hodgdon has to say about using 777 in percussion guns:
Select the proper charge from the loads listed in this brochure. Set powder measure as indicated. While holding the firearm vertically, slowly pour the measured charge of Triple Seven or Pyrodex into the barrel. Seat the projectile firmly against the powder . Make sure that there is no airspace between the powder and the projectile.
Because your revolver is original, and its metallurgy was not as precisely controlled as today's guns, I'd avoid 777 altogether.
Use Pyrodex P or FFFG black powder.
"And lo, did I see an ugly cat. Smoke. Brimstone. Holes in parchment. And this ugly cat was much amused." --- The Prophesies of Gatodamus (1503 - 1566)