Been shooting BP in revolvers for 30 years. Leave assembled, clean them with water, wipe down and oil with Ballistol. Dribble a few drops of Ballistol into the action after cleaning. Disassemble once a year or so. Find greasy black soot in there, but no corrosion.
Process. Remove cylinder, place in sink under hot water tap, let water run over cylinder. Slide frame over tap so hot water runs down barrel for a few seconds. Shake cylinder and place on paper towel. Wipe off all visible fouling on frame with damp rag. Dry cylinder and frame with rags, run dry patchs thru cylinder and barrel. A few q-tips for various crevices. Run ballistol patch thru cylinder and barrel. Dribble Ballistol in action and work a few times. Dribble in ejector and cross bolt retainer as well. Reassemble and wipe down with old greasy rag kept for purpose. Takes about 5 minutes a gun. Colts, Rugers, S&W/Uberti top breaks.
My tip: I have a nose spray pump with the sucker straw removed, filled with water. Take that to a match with me, use to mist gun and wipe down with rag between stages, just to keep them pretty. Also, stick in rifle muzzle and pump once to keep fouling moist and soft.
Water is your friend! So is Ballistol, though there are other BP friendly oils and solvents out there.