The velocities I measured from my ROA are not that out of line with the velocities measured by Lyman. Most of the serious muzzleloader target shooters say that Schuetzen is pretty much interchangable with Goex. With a revolver, you have a lot of gas leakage from the cylinder to barrel gap and that will give you lower velocities than a comparable single shot pistol of the same barrel length will give you.
One thing I have noticed is that if you calculate kinetic energy of the bullet, the relationship of kinetic energy to powder charge is nearly linear. Cut the powder charge in half and you cut the kinetic energy of the bullet in half.