Moose milk....ask ten shooters for the recipe and you will probably get twelve answers.
Basically you use a water soluble oil (Ballistol is one. Cutting oils are another), a detergent (Murphy's is very popular), and water (mostly water).
There are other additions...like alcohol, hydrogen peroxide, ammonia. Each presents a problem _ alcohol and H2O2, both deteriorate ( the H2O2 releases oxygen, not the best thing if you want to avoid oxidizing the steel) and household ammonia, can attack the barrel steel. Ammonia as found in a cleaner like Sweet's is a different animal.
I have been using Murphy's Mix, 1/3 Murphy's Oil Soap, 1/3 drugstore rubbing alcohol, 1/3 drugstore Hydrogen Peroxide for close to 20 years.
The Per Oxide concentration is so low, only about 3%, which then gets diluted to 1% when combined with the other ingredients, that it does not cause any rust. If it caused any rust I would have seen it by now. Kept in a sealed bottle the alcohol does not deteriorate, it stays in solution.
The point of this is that the water in the mix: 80 or so percent of the alcohol and 97% of the Per Oxide does the actual dissolving of BP fouling. The Per Oxide just gives it a little bit of fizz to help lift stubborn BP fouling deposits, and the alcohol helps the mix evaporate faster. Once the water evaporates the oil soap remains. BP fouling saturated with oil will not absorb moisture out of the air, so whatever BP fouling remains becomes inert and will not cause any corrosion.
Why go to all this trouble when plain old water will dissolve BP fouling?
Because you don't have to get the water out. I just leave the oil soap down inside the mechanism of the gun. No rust. So detailed disassembly is not necessary. I have taken apart revolvers that had not been cleaned inside for several years. Plenty of black, oily guck inside. No rust.
Here is a Colt that I took apart for the first time in a few years. Plenty of black, oily guck.
Here is the same Colt cleaned up and ready for reassembly. No rust.
Been doing this for close to 20 years.
It works.