Re: 6.5 grendel for elk?
I've built quite a few Grendels on the AR platform and one on the CZ 527, and quite a few of those were for guys that wanted to take their AR deer hunting. It's not a bad choice for that. 120gr bullet at 2500 fps or the 100gr at 2650+ makes good deer medicine. A few deer were shot at just over 300 yards and none went more than 40 yards. It is an accurate little cartridge with light recoil. I think you can push those velocities a little higher with a bolt action or single shot too.
For elk, hell yes it would do the job, but I'd choose something bigger since that 'perfect' standing broadside shot doesn't always present itself and if I'm elk hunting, I want to fill my freezer with elk meat even if that bull is standing quartering to me.