Possible barrel/chamber problem?

[KurtBiz]

Happened again today. Factory-built Noveske 8.2" NSR upper, factory-loaded Remington UMC 115 gr. Loaded 10 rounds in mag, chambered, fired fine, loaded 10 more, chambered, fired fine, loaded 3 more rounds in mag, chambered (not noticeably out of battery), CLICK.

I had to mortar the rifle in order to extract the live round, which had a light primer strike, and of course the "ring" around the bullet.

Does anyone have any new insight into what's happening here, and how to fix it? Whether it's the upper, or the ammo?

[BobbyG]

1. If you use a standard carbine buffer and spring the bolt cycling issues should go away.

2. The firing pin craters look inconsistent and I'm wondering if the bolt timing?

3. I enlarged the area and the ring actually appears to be copper. If the brass case wasn't chamfered before the tip was inserted, there's a likely chance the copper might have been created when the round was assembled at the factory.