Depends what you mean by big game hunting. I know guys in Texas and Hawaii that use em reliably with the .223 Hog Hammer ammo to put down pigs in thick brush, close action scenarios where quick follow up shots on angry hogs is helpful. But your typical short barrelled AR in 5.56/.223 isn't necessarily the best choice for putting distant shots effectively on deer, elk, etc. Maybe if you're stand hunting and are shooting 50 yards or less at a deer it'd work out, but not if you're trying to put a 150-300, 400 yard shot on a bull elk (or 650 yard shot with a .380 if you're Larry).
I have a ar in 6.8spc2 that I shot 95 grain ttsx at 2900 fps.. it is effective to about 450 yards before the bullet stops performing.. I mainly use it for coyotes but i would not hesitate to shoot a pig, deer or elk with it inside 350 yards. Just have to know the limitations of the bullet your using
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One member posted about his daughters first deer, I think it was buckhunter. In one of the pictures she is shown holding a AR style rifle. I don't remember if the cal. Was mentioned. So yes u can use one for big game. Just know it's limitation. Personally, I wouldn't.
