Sorry I have a Grendel for sale also and got confused!
.750 gas block
1/7.5 twist
Believe it is rifle length gas, will confirm
looks like federal 90 GMM factory was just under or over 1”, best group 0.65” for 5 shots
Hornady 88 ELD factory ammo 2670 FPS, same accuracy just under or over 1” with me shooting