Cycling Issue

[BluntForceTrauma]

The short answer is, that it is a case with a lower designed Max operating pressure, about 52 ksi. Most brass for which the thumb rules apply is designed for ~60 ksi pressures.

Bill Alexander once told me the Grendel case is like any other modern standard brass case — it can withstand ~60k psi with the rest of 'em.

The limitation is not the brass case. The limitation is the bolt. Not the absolute strength of the bolt, but the longevity of the bolt, the fatigue strength, over the repeated hammering of many thousands of cycles.

Because any AR15 caliber with a case head larger than 5.56 but constrained to the AR15 bolt has a "weakened" bolt, the maximum average operating pressure of the 6.5 Grendel has been held to around 50,000 psi.

Bill was always engineering very conservatively, with an eye toward durability and reliabilty, and wasn't willing to chase muzzle velocity just to impress the gullible.

He let those beautiful sleek 6.5mm bullets chase the velocity for him. . . .

Muzzle Velocity versus actual Impact Velocity on target — it's not how you start that's important, but how you finish.