I'm using the 123gr AMAX / ELD in my 24" 6.5 Grendel barrel, I would recommend you try them out as the 123gr bullets and the 6.5 Grendel go together perfectly!
My shooting buddy shoots a grendel with a 20" black hole weaponry barrel 1:9 and shoots 1/4 to 1/3 moa consistently at 100yds with 123 eld and varget in some hornady cases.