We are doing a 6.5 Grendel bolt gun right now under licensing from Alexander Arms. We will also be doing some AR-15 6.5's pretty soon.
The AR types will be Alexander built with our tweaks and furniture.
It is a true 1K round from an AR. The only drawbacks are that at say 100 yards, the groups will not look as good as you may wish because of the bullet configuration and rate of twist and velocity. The rifles really shine past 600 yards though.
You wount be getting 1/2" 100 yard groups, more like 1", but you can get 6" 1K groups providing you and the conditions are right.
You launch a 142 GS SMK os a 139GR Scenar at 2600 FPS. The things are just not "stable" for a 300 yards.
I have spoke with Bill Alexander at length about this chambering. The bolt rifle is an OK idea, but this round was made specificaly for gas guns.
Range and accuracy at range will be better than the 6.8. I think the 6.8 is OK but it is better under 600 yards. Hell for entry and city work, I feel the 223 with a decent bullet is just fine.
I spoke a bit with a Marine who was home from Iraq and he said the M-4 with the Gold medal SMK loading was really opening some bad guys up. It worked very well he said. Much better than the SS-109 and standard ball ammo.