6.5 grendel minimum case length

[lrgrendel]

Shooting a 24" ALexander Arms OVERWATCH with Lapua brass. Fired 100 virgin cases and they all now measure 1.512-1.515.
Alexander Arms publish a minimum of 1.520.

What is the worst that can happen?

 

[vagrendlier]

I have a 24" grendel and have some Hornady cases that have been fired 3 times and still haven't got to 1.520. The AA and Lapua brass will stretch even less. My upper has 650rnds +/- w/no issues