I shoot nothing but black powder and have been using a Hornady Magnum Ultrasonic cleaner on the for a couple of years with great results. The Hornady gun parts cleaning product works well, but I've changed and use Moose Milk to clean them. I take the gun apart, put in the tank and and a dash of Ballistol to the water. I let the ultrasonic cleaner run about an hour. Then I pull the parts out, blow off with my air compressor, lube the cylinder pin with neat Ballistol, spray a dash of Ballistol into the action, run a couple of patches down the barrel, reassemble, wipe down with a Remoil wipe and am good to go. I've never had a hint of rust and the guns are squeaky clean.
I've done this with 58 Remingtons, Ruger Old Army's, Colt Dragoons and Model P's. The guns are cleaner and it's the easiest method I've found.