Mike pretty much nailed it. Seating conicals can be a challenge, an to shoot well they need to be seated straight....you'd not expect a cartridge revolver to shoot well with bullets cocked to one side or the other, a percussion is just as picky.
Some guns just don't seem to have the loading space (try getting 36 conicals into an 1862 pocket navy) and other shooters don't like to stress the pivots of the loading lever.