Some of the milsurp ammo being brought in from Europe or Far East is corrosive. Modern cleaning solvents will not touch corrosive residue in barrels because they have been reformulated to remove the water that was present in the old G.I. bore cleaners. Corrosive ammuntion has potassium chloride present in the cartridge primer. When fired this salt works its way into the crystaline structure of the rifle bore as the barrel heats up.
The rule of thumb in the days when corrosive ammo was the norm: clean your rifle the day you shoot it and for three days there after. Dry the bore and give it a light coat of oil between cleanings. The reason for this kind of maintenance was that the salt leechs out of the steel over a period of four days. This was the only way to make sure the salt was cleaned out to preserve the barrel.
OK, what to do if you have corrosive ammo and modern waterless bore cleaner? Answer: Use hot, soapy water. Any good soap will do and make sure the water is hot. Clean the barrel until the patches come out clean. Dry it thoroughly and oil it. Repeat for the next three days to get the salt out.
So how do you know if your Euro ammo is corrosive? Pull a bullet, dump the powder, load and fire the primered case against a piece of bare steel. Clean the barrel, dry, and oil it. Let the steel sit exposed to the elements overnight. If the primer was corrosive, you will find rust where the primer salt was deposited. No rust, then you've got non-corrosive ammo.
I cannot emphasize too strongly the danger to your barrel from corrosive ammo. I had an SKS that I shot with some premium Yugoslav 7.62x39 ammo. I did not know it was corrosive. I cleaned my rifle after firing the same way as I always do and then sat the SKS in the rifle rack for about three weeks. When I went to open the bolt, I found the bolt was frozen. I kicked it open with the heel of my shoe and found all sorts of greenish corrosion in the rifle from the corrosive ammo. Fortunately, the Russians chrome plated all the sensitive parts of the SKS for exactly this reason. The rifle cleaned up without any problems and there was no corrosion damage to anything.
