Excessive pressures in a factory 6.5 Grendel AR will happen quite a bit before reaching the point where the pressure is evident from reading signs on fired cases.
Working with a pair of (Liberty, a subsidiary of Satern?) 6.5 Grendel 20" and 24" rifles, I (maybe) gleaned some knowledge.
My earliest indication of excess pressure was sooting on the case necks, happening because the case was getting yanked while there was still significant pressure in the barrel, and some of the rims had some damage, too. The cases were still tight against the chamber wall, and were resisting extraction bigtime. Because this was only happening in the 24", I also suspected that dwell time was far longer than the 20" (Both used rifle lengths gas). In this case, the fired primers appeared to be well under max pressure.
I did not recognize all this as "whoa time", and kept incrementing. In fact, the moment I exceeded the bullet maker's powder charge data; the extractor broke. It has now been replaced with a JP Improved Grendel extractor, and has also been dedicated for Speer 90gr TNT bullets; which it shoots like a true Varmint rifle.
The 20" barrel has not shown these serious issues; and this rifle is being worked up for 120gr Gold Dots. BTW, I did purchase a duplicate 20" barrel for long term service.
Will check back with results when I have that part of the 6.5 Grendel project done.
Greg