05-09-2014, 04:18 PM
Don't sweat them. When a cartridge feeds up from the magazine, it travels at an angle and impacts various features of the barrel extension and chamber. This is a fairly violent process as the cartridge is driven forward by the mass of the BCG and buffer propelled by a big honking spring. It can also pick up marks when the ejector pushes it against some of those same features. It's the nature of the beast.
Waiting for an AR in .45-70 with a 30 inch octagon barrel, case hardened receiver, and extra fancy walnut furniture. Until the day someone makes one, I guess 6.5mm Grendel will do nicely.