My Grendel AR's are 20" and 24", with AR Stoner (allegedly Saturn/Liberty button rifled) barrels.
Comments I have seen on other sites suggest that the 123 SST load optimized for the 20" and 24" barrels is 123 SST and 29.0gr W748 (29.6gr for 18" and 22" barrels). I still haven't gotten out (the heat is still triple digits here) to shoot/test these rifles and loads, but I am already betting heavily on this load. I intend to do comparison testing against Hornady Custom 6.5 Grendel 123 SST factory loads.
I will also be testing a trial load with 90gr TNT against the American Eagle 90 TNT Varmint/Predator factory load.
I suspect that these loads will work equally well with bolt guns of the same barrel lengths.
...And if the stars reach the right alignment; I may be able to get away with obtaining a Ruger American Rifle Predator 6.5 Grendel (22" barrel), and succeed in confirming my suspicions... (SWMBO has spent tons in the last six months, and all further expenditures are on her s**t list.)
It ain't easy being green...
...And I may be an old fool who's so far round the bend he can't see here from there...
Greg