I just got my first AR and been studying all the calibers for an upper that can extand the usefulness of the platform.
The 6.5 Grendel looks like the best of anything out there. Longer range and harder hitting for targets or hunting. (or zombies if that is your fear) Not from experience; but, just looking at the charts and reading the reviews. None of the negatives amount to hill of beans. it needs a special bolt, so buy the whole upper or get a matching barrel and bolt. You loose some magazine capacity, but it does use standard metal AR magazines. The blackout and 6.8 both use the smaller 223 case and IMHO the little extra capacity from the Russian case is desperately needed to extend the 223 with a larger bore.
I am also intrigued with the 458 socom, but; that is a whole different deal. That works, due to even larger capacity and if it ever really caught on the brsss would be good fodder for a bigger and better 6.5. Until then, the Grendel seems like the clear winner. It does take the 223 to the next level.
