I see what you're talking about in the picture. I took the BCG out again to inspect, but nothing's in that spot on the opposite side. Must just be the lighting.
Maybe it is brass and it just looks like copper for some reason.
I also notice a little bit of wear in the upper receiver on the right side near the gas tube. I can't get a picture that shows it well, but looks a little too far forward to be caused by the gas key. I found a picture of someone else experiencing similar wear in their AR. Mine's isn't nearly this worn, but it's in the same spot (this is not my gun, just one that shows wear in the same spot):
https://i.imgur.com/0LOQiss.jpg
Oddly enough, I checked one of my other ARs and it has the same wear marks there.
Bookmarks