I'm also thinking it's a head space issue. Too shallow a bolt face or too short a chamber... IDK...
I have a PTG Grendel go gauge that might be about .0005" too long. That half a thousandth won't let my bolt close that has a .135" deep bolt-face. However, the bolt from my 6mm ARC will close on that gauge when installed in my Grendel. It takes a little bit more pressure on the carrier to get it to close though. That bolt is .1355" deep. Both bolts easily close on a Manson go gauge in the Grendel. If I would have had the second bolt in the Grendel first, I wouldn't have known the gauge was a bit long.
I have a PTG Grendel go gauge that might be about .0005" too long. That half a thousandth won't let my bolt close that has a .135" deep bolt-face. However, the bolt from my 6mm ARC will close on that gauge when installed in my Grendel. It takes a little bit more pressure on the carrier to get it to close though. That bolt is .1355" deep. Both bolts easily close on a Manson go gauge in the Grendel. If I would have had the second bolt in the Grendel first, I wouldn't have known the gauge was a bit long.
I refuse to be victimized by notions of virtuous behavior.