I'm inclined to agree with the extractor opinion, but have two VERY BASIC questions first.
1. How long did you have the rifle before you noticed the marks beginning to build up?
2. Did you have any work done on the rifle before the marks began to mar the finish?
If the answer to number two is NO, and the answer to number one is almost immediately, You probably have a warranty issue that can be resolved by simply taking the rifle back to the seller/manufacturer for warranty work. If the answer to number two is yes, you need to talk to the person who last worked on the rifle (depending upon what work they did of course). Good luck.
JeffVN