I tried searching for this but no luck. Anything wrong with slapping a 6.8 upper on a 5.56 lower other than it looking stupid or some thief stealing my rifle and putting the wrong ammo in it? I see a lot of lowers marked "Multi" and haven't ever seen one marked 6.8. Just temporary, want to order a Bison Armory upper but don't have the cash for a complete lower so would just swap it onto one of my existing 5.56 lowers for the time being.
ETA: Or if I'm just an idiot please say so. I've never looked into 6.8 until about 20 minutes ago.