Black powder guns seem to work better with black powder but some folks unfortunately have a hard time getting any so they're stuck with the other stuff. As mentioned, use a fast evaporating solvent like acetone or 100% alcohol fuel to slosh the oil out of the nipple area. I lower the hammer on a piece of rubber to seal the nipple and pour some solvent down the barrel and pour it out to take the oil with it. An air compressor is great for blowing out the excess but a patch works too. I load the charge in the dry barrel and then run an oiled patch down and up the barrel to protect the bore.