The primers used in Russian ammo for about 15 (+) years have been Non-corrosive. This info was stated many times on " the AKfiles". Seasoned owners on SKSboards can also explain.
I've shot many thousands of rounds total, shared by three (former) SKS, four imported AKMs and my imported Czechpoint VZ-58 ; >>kept a piece from Each box: 2,300 rds. in a bag << so far used in the VZ.
All of those guns usually go about 2 - 8 weeks before Any sort of internal cleaning. They are regularly wiped on all external metal surfaces.
No indications of any corrosion have ever appeared, in any of them.