My .308 AR 10 is denting case necks. It may have been doing it all along but I had previously been giving my brass to a friend that reloads .308. I'm now reloading .308 so I just started noticing it. My dies straighten it out but when I'm chamfering the necks I can feel a bump (presumably where the dent was). As I read this I'm thinking I should put this in the reloading section but since it's a function of the rifle that's causing the initial problem then maybe I'll get more great advice here. Thanks in advance for any help you can provide.

Generally occurs when the brass hits the shell deflector.

You can try clipping 1 to 1.5 coils from the ejector spring.

You can try an adjustable gas block, turned down slightly, so slow extraction.

You can try adding a piece of Velcro to the shell deflector to soften the impact.

Or any combination of the above.

I think you hit it with the gas block adjustment. When I set it up I could never get the bolt to hold open on an empty mag (magpul mags). I gave it a couple of extra turns trying to get it to hold open but it never did and I didn't go back and re-set it up. It's probably just over gassed at this point.

Thank you for your response, I think you nailed it.

As a reloader I do what I can to save brass.  I've got a creedmoor and it too some figuring out to stop getting dents in the case shoulder.

Good luck.

I'm cutting it back. Few .308's will lock open on an empty Magpul mag so you just open the gas block until it full cycles and see where your cases are landing. Ideally they'll land at about 2:00 O'clock. Mine are landing at about 4. Haven't been out to the range since my first post but I'll get it done next week if the wind will let up a bit.