worried about what looks like rust.
so i just got my rifle a couple of weeks ago and was going in to do some very up close inspections last night. Where the round feeds in there was some markings that looks a bit funny. I can't find what the name is but if your looking down the barrel and there is the part that looks like a gear type thing right before the barrel. I had the upper off and had bright light going inside the upper and it looks like copper/rust type crap. It wasn't really so much rust looking, but just a dark brown. I tried to clean it off with some hoppes and some Qtips but nothing really came out of it. Just a little bit of powder I guess from when they shot the weapon. Also behind the "teeth" where the Delta ring would start from the inside there was more brown crap that I was unable to get off. Any idea what this is or could be? Thanks guys. I will try to get pictures today but the angle is all messy and hard to do.