You didn't say if your rifle is flint or percussion, so either way plug the little hole the fire goes in, stand the rifle, or just the barrel, so the barrel points straight up and pour any solvent into the barrel (there is no magic formula) let it stand a while then empty the crud. You should be nearly grease free. If not, repeat the process until you can clean the rifle in the normal manner to finish he process. No mumbo jumbo, just simple stuff.
If you want to mix some secret sauce look up the formula for Ed's Red solvent. It will do anything a shooter needs doing.