I built a 6.5 Grendel with a 24" barrel, Muzzle Brake
, Jewel trigger, on a bushmaster lower. I've been shooting Hornady 123gr A-Max factory loaded bullets. I have over 200 once fired cases now and will be reloading with Sierra 120gr Matchkings. So far this caliber has exceeded my expectations.
I have a DCM Compasslake match service rifle 1/7 barrel and have competed in matches to 600 yds for the past 15 years. It's a custom build with open sights. It still shoots great.
My 3rd AR is a 1/8, 24" barrel Varminter. It likes 75gr Hornady Match bullets. I've taken coyotes and jackrabbits with it out to 700yds. Reading the wind is extremely critical.
That said, I built the 6.5 Grendel over the 6.8 SPC because beyond 400yds it's shoots flatter and handles the wind better. I've shot out to 800yds consistently with excellent accuracy. It's on a Bushmaster lower. The benefit is I can switch uppers if I choose and have taken 3 uppers into the field several times.
When it comes to shooting accurately at long distance the 6.5 is hard to beat.