I shoot at an indoor range these days (moving to an urban area kinda forced me into it) and I'm getting used to the environment with one exception; flying brass. There are full height walls between each lane so you won't eject hot brass onto the guy next to you (this is good) but I'm getting empty brass ricochets off the wall as I'm firing. Last time I was on the range I caught a couple upside the head, 3 down my sweatshirt, and a couple bounced off the slide. After I got home and tore my M-A1 down for cleaning, I noticed a brass colored mark on the top of the slide. It appears that, when one of the ejected shells hit the top of my slide, it actually left a mark. There isn't a gouge or other indication that the finish was compromised, but I can't seem to get the brass residue to come off either. Long story short, how the bleep do I get it to clean off without screwing the finish? It's just a fit and finish question, but has anyone else experienced this issue?