I have about 400 rounds of old "Wolf" brand 7.62x39mm FMJ ammo. It has polymer coated gray casings, and they were stored in an old car for 10 years. they show signs of rust coming through the polymer, and I'd like to know if that's going to become a problem. Since I fire 50 rounds or so rounds each shooting session, I should eat them up within a few years, but will they last that long? and will they cause any issues with my gun? they seem to work fine in my SKS.