[ptomato]

The AR-15 is almost certainly the most-used gun (not a majority, just more used than any other model of gun) for hunting in the US, though it's more common for varminting than for medium-large game. Hunting e.g. whitetail deer with .223 is fine even, though you're somewhat restricted in shots you can take for a humane kill vs. other calibers.

Also, it's a perfectly reasonable gun for home defense - compared to e.g. a 12 gauge shotgun which is commonly recommended, a typical AR-15 length (with extendable stock extended) might be around 37", whereas a typical 12 gauge shotgun even of the tactical variety (I.E. with an 18" barrel instead of a 24 or 28" hunting barrel) would be at least that long, but usually a bit longer. #00 buckshot has about the same drywall penetration as .223 FMJ, but using JHP (preferable anyway for defensive purposes) instead significantly reduces that.