I don't believe this to be the case. My 6.5 Grendel was acquired specifically for Antelope, and I think it'll work well on deer and the occasional 'yote. I got my .458 SOCOM for Feral hogs, and it's a hog hammer! Those with a 6.8 can go up to deer size game, and I know folks that use .300 Whisper (or Fireball) on deer or feral pigs out to about 100-150 yards. In a survival situation, I believe with the right bullets and shot placement a .223 would take up to deer size game out to 200-300 yards depending on the bullet. There are also those AR's chambered in .223 WSM, .243 WSM, and .25 WSM. I don't think I'd try hunting with FMJ bullets in an A2 rifle, but the right bullet with a scoped gun should work; you'd just have to make sure you were within effective range for whatever caliber you've got.