I often use 26 grains of FFg in my 1860 when shooting round ball. Velocity is a bit below that of an equivalent charge of FFFg, but I've won enough matches with it that I don't worry about it.

Keith advised using a tallow-soaked felt wad under the ball. This was something he'd picked up from Civil War vets or their contemporaries. If you want to give this a try, his source of felt was old felt hats. The felt was dipped in melted tallow and allowed to cool, then the wads were punched. If you don't have a wad punch of the correct diameter, a 45 caliber rifle case or pistol case can be used. Lay the lubed felt on the end grain of a piece of soft wood, press the case mouth on the felt, and give it a smack with a mallet. If you're going to do much of this, drill out the primer pocket with a 4-5mm drill bit and poke them out with a splinter of wood.