In 1950, the .222 Remington cartridge was
developed for varmint hunting. It evolved into the .223 Remington round, which in turn became the basis of the 5.56 mm cartridge adopted by the military for use in the M16 and favored by many target competitors. Neither round is preferred by deer hunters, as most loads are too underpowered to harvest big game.
Maryland game
regulations require that rifles used for deer hunting must use ammunition developing a muzzle energy of at least 1,200 foot pounds. A
typical 5.56 with a normal 55 grain bullet generates 1,223 ft.-lbs. of muzzle energy. By contrast, a. 308 round with a 150-grain bullet fires with 2,648 ft.-lbs. of muzzle energy, over double that of the 5.56.
As is plain to see, the power of the .223/5.56 round isn't much to speak of compared to typical hunting rounds. It is so underpowered that the Armed Forces are replacing its 5.56 M16 and M4 rifles with a new 6.8 x 51 mm round (the XM7) which has muzzle energy of 2,267 ft-lbs with a 135 grain bullet.