With the exception of the M1 Carbine, just about every firearm used by everybody from every country up thru the Korean War was corrosive primed.
Corrosive simply means that the primer is based on potassium chlorate instead of lead azide. When fired, it burns to potassium chloride, a first cousin to table salt. If left in the barrel, in a humid climate, it starts to rust.
To remove the residue, it needs to be dissolved. Salt does not dissolve in petroleum, but it does in water. Windex, etc will get it out- but mainly due to the water in windex.
Many of the Communist bloc weapons were made with chromed bores for that reason. I shoot a fair amount of several misurp calibers that IS corrosive primed.
After shooting, I remove bolt, place gun in a padded vise, muzzle tipped down. Get a plastic funnel from the dollar store- one that will fit into the chamber. place bucket on floor under muzzle. SLOWLY pour about a quart of HOT water thru the bore. Put a couple of drops of Dawn dish detergent on a bore brush, scrub bore. Pour a second quart of HOT water thru the bore. Wipe bolt face, chamber area, etc, with damp cloth. Gas piston and gas tube need washing out also. Let gun drain and set for 5 minutes, heat will finish drying the bore. Run oiled patch thru bore, wipe bolt with oiled cloth.
GI bore cleaner from WW 2 will work also, but washing out the salt is the important part.
What we have here is... failure- to communicate.