Quote Originally Posted by RealFastV6 View Post
Basically you have a C traveling inside of an O. Eventually, you'll see two lines inside the upper where the two rear bottom edges of the carrier is impacting the upper receiver.

Not sure how to elaborate more. It's not really a big deal, but it's inevitable.
Interesting. I have not seen this. Typically the BC contact with the upper receiver is on the four raised rails on the BC.