I think the nitrites, left behind after burning BP, combine w/water vapor in the air, to form weak nitrous acid. It disolves steel slower than stronger nitric acid, but is still corrosive enuff to do immediate damage in the presence of water.
If that's not bad enuff, sulfur dioxide, also produced from burned BP, combines w/water, in the presence of nitrites, to form sulfuric acid, which is a strong acid.
70% Rubbing Alcohol is 30% water. It's the water that dilutes the acids so they can be wiped away. Isopropyl alcohol is insoluable in salt solutions.
As far as I know, there are no chlorides in BP or it's burned residues.
So, knowing all this, it's prolly better to use pure water w/a little water-soluable oil in it, as a preliminary BP solvent. Dry the bore quickly, & follow up w/your favorite oil. Oil keeps the water vapor off the steel, like a barrier.
If ya don't have BP solvent available out in the field, oil is the best thing to coat the bore, lock, & all metal parts. It keeps the water out. No water, no acid formation.
Boiling hot soapy (bar soap, like Ivory) water, for over 300 yrs, has been the best solvent for a full cleaning at home. Hot steel dries quicker & hot steel takes oil into mating surfaces better, like breach plugs, sight dovetails, tennon dovetails, touch holes, nipple threads, etc.
Bar soap water is mildly alkaline & stops acid action, but must be dried quickly and immediately followed w/oil.
Kindest Regards,
Doak