Oh goody, another pyrodex verses black powder row
Pyrodex and black powder both produce caustic salts on combustion.
The only known practical solvent for salt that is readily available is water. Hot is even better.
Use that with pyrodex and or BP and your barrel will be fine.
Use anything else and one is risking damage.
Remember, nothing really isolates salts or chemically neutralises them. All we can do is dilute them and wash away or in crystal form hold them in suspension. Unfortunately mineral oil based product do not absorb and hold salt in suspension. It may seem as though they do at first but after a while the salt separates from the oil, absorbs water from air and forms a micro caustic bead.
The only oils and fats that will carry a measure of salts and retain it are animal and vegetable.