The rule I follow was oft quoted years ago: you cannot overload a blackpowder revolver with blackpowder.*
*Steel frames only, BP substitutes like 777 were not invented yet.
If you use more lead (conical or double ball load) you have less room for powder. It is that simple. A conical will take up more room therefore you can't put in as much powder or filler. I use 30grs (vol) of BP in my Remingtons as a maximum load when shooting conicals. No wad or filler. It is a nice "thumper".
With over 15 perCUSSIN' revolvers, I've been called the Imelda Marcos of cap & ball.
SASS#3302 (Life), SASS Regulator, NRA (Life), DGB#129
Wolverton Mtn. Peacekeepers (WA), former Orygun Cowboy (Ranger, Posse from Hell)