Over-gassing/Timing Issues

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Thinking cap time. This maybe a post for the reloading forums.

I am having issues with belting in my 6mm ARC handloads and I am pretty sure it is timing related, but not sure completely. The combo is a 108gr Berger Elite hunter on top of 26.5gr of Varget using a Federal GM205M primer. Starline Once fired 6.5 Grendel formed at 1.182" HS (B350). COAL is 2.280". Velocity is at 2445 fps.

Here is my current built:
Anderson RF-85 upper
Proof Research 18" barrel in 6mm ARC
Rifle +1 gas system w/ SA AGB
JP Enhanced 6.5 Grendel bolt
Brownell's (I think) phosphate carrier
A2 rifle buffer spring and tube
A2 rifle buffer: replaced the aluminum spacers with steel weights from a standard carbine buffer (estimated total weight around 7.5 oz.). I will verify the weight tonight.
ASC 6mm ARC 5-rd. magazine.
Custom 6mm silencer.

When utilizing this load with 6 clicks from closed of the AGB, I did not have any belting*, the action cycled, but the bolt did not lock back. 7 clicks the bolt locked back and there was a slight noticeable belt that I can barely feel with my fingernail, but could not see with a naked eye. 8 clicks the bolt locked back and I noticed the belting occurred maybe a few thousandths up the case.  At this time I did not inspect the cases, for whatever reason.

Two days later I utilized that same load with 20 rounds with 7 clicks from closed on the the AGB. Half of them had belting on them.

Here are the big questions: Is my extra heavy buffer causing timing issues? Is the AGB opened up too much causing the case to begin extraction before pressures drop in order to compensate for the bolt not locking back?

*The way I measure belting is measured in feel and measurement. Belting seems to begin occurring at the webbing measuring 0.4405-0.441"

Is this what you refer to as belting?