It is my believe that the black stuff referred to as "carbon" is actually an collection of baked on almost all non-carbon powder and primer residues. If the black stuff was carbon it would be extremely difficult to dissolve, and stuff used to do this would harm a barrel. Commercial bore cleaners would not touch the carbon. Instead, various bore cleaners use relatively cheap industrial chemicals that either attack and dissolve copper fouling and the metal components in the black crud - copper, lead, antimony, tin or bind (chelating agents) with these components facilitating their removal. Some bore cleaners use chemicals to retard evaporation. The chemical action of solvents on the black crud facilitates the scouring or scrubbing action of a tight fitting bore and results in mechanical removal of the black crud. Stubborn remnants, yield to abrasive cleaners like JB. Stainless steel is not entirely stainless and can be subjected to surface reactions.
Upon combustion the nitrocellulose and nitroglycerine are converted to almost entirely gaseous components, like CO2, Nitrogen, Oxygen, and steam. The presence of impurities like sodium bi carb or calcium carbonate have no effect on the mole (just a number) multipliers on each side of the reaction (it goes bang - it does not produce carbon fouling or create carbon compounds other than gasses like carbon dioxide. The nitrocellulose impurities are miniscule, like remnants of unwashed sodium bi carb to neutralize the acid used to make the powder but other stuff is added to powder as deterrents, flash control, and stabilizers and calcium carbonate is added to retard acid action during ball powder storage (less than 1 %). Tiny amount of graphite, to lube up powder grains and disperse static and carbon black are added to avoid translucent powder grains. Some solvents contain a chemical that dissolves nitrocellulose but that is not "carbon"
I saw comments regarding the inability of various agents to remove the black stuff - this may be expected as the reactions with black gunk are time dependent. I have now started to warm my barrels so they are warm to the touch with a hair dryer (watch for sparks & propane propellant- warm then squirt) while chemicals are working inside the barrel and thus speeding up the reaction also give them time to work. Some old chemist guy, Arhenius (sp?) established chemical and other reactions were pushed by temp increases. Squirt the solvent stuff into a hot barrel at the range.
I use a commercial foam cleaner, 0-20W synthetic detergent motor oil, and nice tight fitting nylon brushes (cleaned with Isopropyl alcohol after each use) and JB or an equivalent abrasive bore cleaner. After a good warm solvent soak, the JB goes on the brush to scrub, then brush is cleaned with Isopropyl, then dipped in 0-20W to float out the JB stuff and black crud then a clean oiled brush followed with flannel patches. Wipe off cleaning rod with paper towels after every removal. Copious quantities of black crud are produced.
Steam would sure loosen and float away carbon in cylinder heads. My thinking: engine top cleaners would attack any stuff binding carbon particles but would not dissolve the carbon. But petroleum base fuel combustion is not like the nitrocellulose combustion process.
I have little more than zippo knowledge of chemistry having studied it some 58 years ago. My method works for me, nice groups, often 3 in one hole - everybody is free to pick and choose.
