Actually, BP is very easy to load. No need for scales, fillers, no double charging, etc. The hard fast rule for reloading is to fill the cartridge to 1/16" above where the base of the bullet seats. Check your bullet dimensions and make sure you set the fill line of your powder just above, so the bullet base lightly compresses the powder. You can use a volumetric measure and once you have your load determined, just pour it in and finish the loading process as with smokless.

I would also recommend using magnum primers with Pyrodex to get more even and consistent ignition. Also, Pyrodex P is made for pistols, as this is a finer powder for better performance in small cartridge cases.