The factory instructions for cap and ball revolvers have long suggested loads that are so weak that you run the risk of getting a projectile stuck in the barrel.
Don't know why they haven't corrected this. I guess the factories don't care about their written instructions.
Anyway, with a .454 ball and Wonder Wad, I'd suggest 20 grains of FFFG black powder or the equivalent volume of Pyrodex P. That is to say, whatever measure throws 20 grains of FFFG may also be used for Pyrodex P.
Hodgdon does not recommend the use of its 777 in brass-framed revolvers, by the way. Anyone tells you they use it in their brass-framed revolver, ask them what ballistics lab they obtained pressures from. It's difficult to get a handle on what kind of pressures you're getting in a cap and ball revolver, since there is no case to measure.
About the only pressure indicators are velocity and another indicator that manifests after you've already entered dangerous pressures: caps disintegrating and the hammer being thrown back from high-pressure gas spurting back through the nipple.
If this happens, you're already well into dangerous pressure -- the kind that can burst chambers and barrels, and stretch frames, especially brass frames.
But as long as you use black powder or Pyrodex P, you won't be able to create dangerous pressures. You can create pressures that are injurious to a brass-framed gun with black powder or Pyrodex P, so don't load your revolver to the gills.
For the 200 grain bullet in a brass frame, I'd suggest you try 18-20 grains of FFFG or the equivalent Pyrodex P. I use 26 grains of FFFG in my steel-framed Remington under the 200 gr. Lee conical bullet, but it's a much stronger gun. I wouldn't go higher than 20 grains.
I'm not so sure that using conicals in a brass-framed revolver is a good idea. Conicals being heavier will create higher pressures, powder charges being equal to those used with balls. You may reach a point early on, in which you enter an injurious pressure level just to get the conical bullet out of the bore.
Balls, being lighter and having a thinner bearing band for the rifling to grip, create less pressure than conicals.
Try 18 grains of FFFG or equivalent with your 200 gr. bullet at first, then increase incrementally to 20 grains. Strive for consistent seating pressure on the bullet; firm against the powder, leaving no space between bullet and powder, but not hard. Seating hard can damage the powder kernels, affecting burn rate, and damage the soft lead bullet.
The most accurate loads in cap and ball revolvers are almost never those that are at or near maximum. Mild to mid-level loads almost always are the most accurate, because they place less strain on the projectile.
