The 6.5 Grendel has better long range ballistics.
But it shoots light to medium weight for caliber bullets with rather middle of the road BC at geriatric velocities ( bettering the 556 by BC only, and then with longer than desired bbl lengths ( what does a 120 grn Grendel do from a 14.5 inch carbine?), eats up mag space badly, is oversize case body wise resulting in bare minimum structure in the breech of an AR15 platform.
Otherwise, the Grendel is a decent AR15 round, loaded to moderate pressures shooting light for caliber bullets.... the best part is the fact that it is a .264 diameter bullet.
I built a 6.5 Grendel. Nice rifle. I like it a lot but I don’t go to battle. My rifle is very serviceable, but I don’t serve in combat. The original design of the Gerand was a .277 round. Army said all ammo out there is .30 caliber. They adapted it I have a M1 Gerand a great rifle but I am so prejudice for it. Get the troops the best, what ever it turns out to be. IMO