[Huck1969]

Thank you for your reply.
I have checked for burrs forward of the barrel extension and inside the bore toward the leade, both visually and with a borescope, and their are none.
As for the magazine lips, the gouge on the case is at the 12:00 position as the round feeds and ejects; the mag being at the 6:00. I just tried using some steel wool, just on the "teeth" of the barrel extension where the bolt lugs lock. After wiping clean I still get the prominent scratch down the entire side of the case.