My son and I have hunted with ARs for a couple years. This last year I kept coming on spots to hunt that offered longer shots than I would want to take with the 556. A smoking sale came up on a 243 Mossy that I picked up for my son. I sighted in my 30-06 but I started toying around with building an upper for the AR....between the 6.5 and 6.8.... The Grendel has been around for several years and from what I have read, is better out further and equal up to that. So I went 6.5.
I would not dump 556 for it but it does outperform 556 in the same sized package. If SHTF I would still carry 556 though. It is strictly a hunting gun for me. If you are looking to get one...learn from my mistakes. Aim and Bear Creek have good prices on some complete uppers. I went the build route