I returned my AR10 to PSA because of fail to extract problems. I did some reading on this forum about PMAGs not fitting correctly. My gun is better since in got back from PSA, but I notice during deer season that it marks up the cases. It sometimes puts scrapes right by the crimp part of the bullet.
Is the PMAG possibly the cuprit?
My Lower
https://palmettostatearmory.com/psa-gen2-pa10-308-complete-classic-lower-receiver-77932912.html
don’t think your upper link is working. takes me to my order list.
I have the 20" SS upper in 308. I ended up purchasing 1 of many types of mags to find what worked and didn’t. I settled on the HexMags - they work perfectly for me and my setup.
Changed link
Scrapes are probably from the chamber/feed ramps.
I wondered about that. Ever tried to smooth them out? What would you use?
Shoot it. That is the best solution.
Inspection mirror and a good light, OR a bore camera (if you have access to one - they’re Handy!). Check the chamber for roughness/adhesions.
Clean appropriately, light polish with J.B. bore cleaner, if truly necessary. 
WARNING! The Chamber Shoulder is what the cartridge is Headspaced on! The Lede/Forcing Cone vastly affect accuracy! Jacking any of those up with over-aggressive or heavy grit polishing, can have Unwanted Consequences!!!
Avoid metal chamber brushes.
OR just shoot the 
out of it, and it will eventually break loose/wear in….