Reading rim sign

[UncleBob]

While on the subject or brass markings these are from a CMMG upper that I just picked up.  I don't quite recall if I was manually feeding these or single shot from a mag, but I almost have to assume these scratches on the necks are from the feed ramps?  Working on my photo skills. I don't have a macro lens so I am using std from a distance and zooming in. 

Looking to see of I can get away with polishing while attached to the upper. I have a 1/8 pneumatic pencil grinder just need to find the right accessory.

As Grayfox mentioned, those are from the barrel extension. Those sharp points and the big hump in the middle need to be knocked down and polished for Grendels and ARCs. If you look up pictures of the barrel extension on the Bushmaster 7.62x39, you'll see there is no hump in the middle. That is the one you want to get close to mimicking. Remove the barrel for doing any feedramp work.