In most states any centerfire cartridge is legal to hunt deer with. The .222 was used years before the .223 came out and it would kill deer(at reasonable ranges) like lightning. I prefer a .30 caliber but I believe the AR15 now is chambered, or can be, for a variety of rounds and I wouldn’t mind owning one. I would especially like to test that .50 caliber round they have adapted to it.
The original Stoner rifle, AR rifles, was a 7.62 NATO, 308 WIN.
That is now designated as the AR-10.
—at a gunshow a few years ago I attempted to do a little friendly kidding of a Leitner-Wise rep, who was extolling the virtue of their rebated-rim version of the .50-70—but he was not amused—
I have shot a .222 with a 24-inch barrel, and it was extremely accurate.