On the buffer of my carbine there are two gouges on the face of my buffer. I've identified that the cause is that the base of the BCG is scraping the buffer face when you open up the rifle and the lower gouge is caused by the buffer retainer. Here's a pic:
It is a BCM Carbine upper and BCM BCG on a Stag Lower. The color on the lower is paint, I was bored, curious and had a can of rustoleum.
I'm not too worried about it because I can't imagine that something cosmetic would cause a malfunction, but is this a common thing? Is something significantly out of spec?