Howdy
I will probably get my head handed to me for mentioning it, I always do when I mention it, but all I have used to clean Black Powder fouling for years now is Murphy's Mix. Equal portions of Murphy's Oil Soap, Rubbing Alcohol, and drugstore Hydrogen PerOxide.
Why reinvent the wheel I am asked. I have been cleaning with hot soapy water since before the Flood. Always worked fine for me! Why spend all that money on special ingredients when water is so cheap? Good enough for the Civil War, good enough for me!
Two reasons. You don't have to heat it. You can use it cold right at the range, before you leave. Reason Number Two: you don't have to dry it out. You don't have to take the gun apart to get it out. You don't have to heat anything to dry it out. You just leave it down inside, wet! Period.
Yes, a large part of Murphy's Mix is water, and it is the water that actually does the cleaning. The Per Oxide is about 97% water, the alcohol is about 20% water. It is the water that does the actual dissolving and washing away of the fouling. The alcohol is just a drying agent, helping to evaporate the water more quickly. The 3% Per Oxide provides a little bit of fizz to help lift off stubborn fouling. But most important, when the alcohol and water evaporate, the Oil Soap remains behind and coats every thing with an oily residue. Here is a little understood fact. If you coat Black Powder fouling with oil, it looses its ability to cause rust. I have been doing this for years. No more heating anything, no more trying to dry the water out. Just leave it down inside. Once a year (or less) I take my guns apart and clean out all the black, oily gunk inside. Always plenty of gunk, never any rust. If you want your guns to be White Glove clean inside, then don't try this. If you need to clean two revolvers, a rifle, and a shotgun at the end of the day, and don't want to spend a couple of hours, try Murphy's Mix.
Regarding chemicals and acids and bases. Forget all that. It does not matter. The real way we prevent rust is by diluting the bad stuff with water and washing it away. Just use plenty of some sort of water based BP cleaning solution (hot soapy water if you insist) and dilute and wash away the bad stuff, forget the chemistry lessons.
One more thing. It was BP fouling coupled with corrosive primers that caused most of the rust in the old days. I have bunches of old guns over 100 years old. Most have pitted bores, some do not. But it was the fouling AND the corrosive primers that did the deed. We don't use corrosive primers anymore, and BP fouling is not as corrosive as it used to be with modern non-corrosive primers.
OK, flame away.