For a Lightweight, deer rig it’s hard to beat the 6.8 in an AR 15. It gets most of its performance in short barrels, and you can have an accurate, 300 yard deer AR that’s under 6#, or less, if you want. Nothing wrong with other calibers, but I’ve got all sorts and can/do build all sorts, and I carry and kill deer with a 6.8 usually. If I was worried about shooting beyond 300, I’d go straight to the 6.5CM AR, or a bolt gun. The longer bullets usable in the 6.5 are better suited than the constraints of the Grendel...to me. I just enjoy a short, light gun when getting in and out of vehicles and stands. I just don’t see any need for the non-standard AR10 for 95% of deer hunting. The Grendel can do it in a short, light package, also. It just isn’t quite as efficient in the shorter tubes, but it’s splitting hairs inside 300.