Help needed, Failed No-Go .300 AAC, pictures of brass.

[JerDerv]

New build.

Barrel: 8" CMMG .300 blackout barrel
BCG: AIM surplus With an RCA adjustable gas key set to lock back on empty mag with subs no suppressor.
Ammo: Magtech 123grn

Current round count is about 200-225 mixed subs and supers.

So last week i put 150 rounds through the gun. I got home and started resizing brass, i had 4 out of the 150 that jammed in the sizing die and formed a ledge toward the bottom of the brass i thought maybe it was the die or possibly not enough case lube. I took a note and set them a side. Picture below.



Today i planned on running another 150 rounds of factory loads before i started shooting my reloads. I kept the oddity in mind while shooting today and kept a close eye on the brass. Heres an odd pattern i noticed, its not every piece its like 25% of the time.



The observant ones out there may have noticed the missing primer. This is when i stopped shooting and picked up all my brass. There was only that one that lost the primer. Upon closer inspection i found a few that had significant deformation at the ejector location and extractor marks on the rim. In some pieces the brass appears stressed as if it has stretched. I cherry picked the worst ones and took pictures.






Gunsmith had a set of 300blackout Go / No-Go gauges. I had a spare PSA Premium BCG. We removed the ejectors and checked with the AIM BCG and it closed on the No-Go. We checked with the PSA bolt and it did not close on the No-Go. He then grabbed a known good .300blk barrel off the shelf and the AIM bolt did NOT rotate on the no go. The gunsmith only did this with his fingers and did not use a punch like i have seen some do to assit in rotating the bolt. I wish i would have had him double check but im home now.

So.... Is it the bolt? Is it the barrel? Is it the ammo? Id like to think its just the bolt as the PSA bolt did not close on the No-go. However with the AIM bolt also not closing on No-Go in a different barrel that makes me wonder. The brass shows signs of problems that i haven't seen before and have no experience diagnosing. Opinions needed!

Gunsmith said just run the PSA bolt...