Guys, I took my AR and HK 93 clones out of the safe, and saw what appears to be the preliminary effects of oxidation in the barrel and flash hider. This was the first time that I've seen this on any of my rifles. After shooting them, I always clean them with the regular cleaning solvents (Hoppe's Elite, No. 9 (sometimes) and CLP. I then out them back in the safe. The last time I fired my C93 rifle, I used mostly Wolf 55 gr. FMJ and may have put a couple of round of PMC brass FMJ through it. Well, here are some pics of what seems to be oxidation. Any idea as to why this happened and what I can do to prevent it from recurring in the future? Thank you.