I know a lot of guys use the cheap steel cased ammo without problems, personally i dont for the reasons you described, some of the ammo comes heavily laquered and can leave it a tight fit, with a tight bolt lift also, known poor oal consistancy aswell, as i mentioned try some quality ammo, ibet you problem dissapeares, there was talk on this side of the pond e/u that red army was corrosive and had a rep for poor accuracy.