Took my build out for a second shake down and this time it cycled. The brass has some different marks than what I've seen on my reloads or any factory brass for that matter.  Looks like a bunch of stress marks on the upper half (neck side) of the brass. There are some pretty harsh ejector marks on some of them, and some burring from the ejector as well.

I had to open the adjustable gas block up about 3/4 of a turn to get the gun to cycle, and I figure it is probably all the way open.  Since I reload I'd like to get it taken care of before I put some good brass in there to get it busted up.






At least it shoots well.  First six rounds that cycled out of this rifle

Its pretty typical for .308 based ARs with standard firing pin hole diameters to
show some cratering/primer flow on the fired cases...this is especially true with
any gas system shorter than rifle length...

JP Precision uses AR 308 bolts that have smaller than normal firing pin hole diameter
to help remedy the problem, they also use a slightly longer gas system length (rifle)
for their barrels in the 308 class of cartridges...

It a plus that you have a adjustable gas block fitted as 308 based ARs tend to be
over gassed from the factory especially the shorter gas lengths like carbine and
mid length gas systems...

Good luck.

What BCG, buffer and gas setup?

Oh yeah that would be helpful

Mega Arms 22" barrel,  Rifle length gas tube
SLR rifleworks Adjustable GB
Armalite AR10 Buffer and Rifle tube  5/3/8 ounces as I measured the buffer.

AP BCG but I swapped out the bolt face with the matched firing pin and bolt face that came with the barrel.
I measured the bolt lug dimensions with the original bolt face from AP and they were identical.  The firing pin looked to be the same diameter, but I did not measure it.

You want weight behind the bolt and an adjustable gas block to slow down the timing on the extraction, that will help with the abuse the brass is taking.  But it's likely to be pretty tough on brass anyway.

As for the ejector marks, your problem is the pressure in the chamber is still slightly too high as the bolt is trying to be turned by the retreating carrier.  This means the case head is being pushed into the bolt face pretty hard as the bolt turns, so the ejector digs into the brass.  Number one, use an adjustable gas block, heavy carrier, heavy buffer and stiff buffer spring.

Second, pull the ejector out and use a fine file or polishing stone and radius the edges off so that it won't catch on the brass, it should be able to slide across it.

What's the diameter of your firing pin right before it rounds off at the tip?

You want the smaller .065 (JP) to .070 (Aero) firing pin protrusion in your bolt face to prevent blowing holes in your primers.

Ejector swipe should be decreased by increasing buffer weight. I swapped in three tungsten buffers to my rifle buffer. 

What does that put your buffer weight up to?

7.8oz

Exactly.

I shoot suppressed pretty much 100% and it's even worse with the additional back pressure caused by the suppressor.

I converted my rifle buffer over to all tungsten weights and also switched from a JP low-mass carrier to a full-mass carrier to try and get as much weight as possible behind the bolt in order to delay unlocking as long as possible.

I haven't had a chance to shoot with the new weight setup, but am hopeful it will reduce the wear and tear on the brass.

I keep these tungsten weights around for modifying buffers.
https://www.amazon.com/dp/B01N6BOH93?tag=vglnk-c102-20