There is no such thing as mildly corrosive.(Or a little pregnant.) The best prevention is immediate cleaning with one of the many products that contain ammonia. I have used Windex, Sweet's 7.62, Hoppe's #9 Benchrest ,Hoppe's #9 Black Powder Solvent (yes, it does work, monsternav.) , and Corrosion X. I shoot a lot of milsurp ammo from my Mosins, Turk Mauser, No.1 Mk III, and Yugo SKS. I clean them that day, as immediately after shooting as possible, or at the very least run 2 patches soaked with Windex (I bring a small bottle to the range with me) down the bore, and wipe the bolt face, then run a dry patch, down the bore and wipe the bolt face dry. I then clean them within 24 hrs. The one time I did not do it, I got rust in one of my Mosins. Lesson Learned. I had shot Black Powder for years before contracting Mosinitis
, so I knew all too well the importance of cleaning quickly and completely.
My favorite solvent is Sweet's 7.62. But even if it's a 99 cent small bottle of Windex, get something, and use it.