I used to pour very hot water down my barrel for cleaning, but then found that I could not dry it fast enough and then lube the barrel to avoid rust forming on the lands. On the advice of a friend, I tried cleaning with tepid ( warm) water and soap, instead of boiling water and soap, and HEY! what did I find but that my barrel was cleaned just as well. The difference was that I didn't grow rust because of the faster drying from heating up the barrel. Black powder does leave some salts, and, of course, carbon in the barrel. The lube burned will leave behind some altered hydro carbons, so a little soap in the water is okay. Just don't over do it. Cool to tepid water is sufficient to clean your gun, and you dry it by upending the barrel to pour out the water, and then running several dry cleaning patches down the barrel to soak up. I blow through the barrel to push any drops out either the touch hole on a flintlock, or out the drum or patent breech of a percussion gun. ( Remove the nipples for a separate cleaning, and re-oiling before putting them back in the gun.) I use a pipe cleaner to clean out the threads for he nipple, before oiling them lightly and putting the nipple back in the gun. A clean patch run down the barrel to the face of the breach plug tells me if there is any gunk left on the face of the plug. If so, I clean some more. Or use a scraper attachment, or in my flintlock, use a pipe cleaner through the touch hole with some solvent on it to clean the face off. Then I re flush the barrel, and then dry it again. I have been using Wonder lube lately for lubing the barrel to prevent rusting during storage. I am trying some different things, based on recommendations I have read in this forum, so this may change. Mineral oil is next on my list to try.