AR-15 are typically 5.56mm or .223, not ideal for much beyond plinking varmints. People do use it, but it might take a couple of shots and you have to watch your range.

For deer or elk, you'd want something like .30-06 or .30/30 or 7mm Rem mag, or even .300 Win mag, but that's a bit much.

People use .223 for hunting deer all the time using hunting rifles. I'd recommend.243 and higher but a .223 does work.