Corrosive ammo leaves a salt behind in the bore and anywhere else the fouling gets to, e.g., the gas system of a semiauto. These salts are hygroscopic, meaning that they absorb moisture from the atmosphere, which leads to rust. To get rid of the salt you need to flush it out with water. You can use plain old water or a variety of solutions, including:
- Soapy water
- A mixture of 1/3rd Ballistol and 2/3rds distilled water
- Simple Green
- Old time USGI Rifle Bore Cleaner as found in green cans at gun shows.
I often use Windex because it has surfactants in it along with the water, which helps it clean fouling.
Contrary to Internet myth, you do NOT need ammonia to "neutralize" the salts.
Just run a few wet patches through the bore and gas system, and anywhere else you see powder fouling. Then wipe it out with dry patches and finish cleaning with normal gun cleaner like Hoppe's No.9 or CLP. When done lightly oil to prevent corrosion.
Check the gun the next day to make sure you got everything.
Some people seem to think that shooting corrosive ammo is like putting termites in your woodpile. Not so. It just requires a little extra maintenance.