Actually, both back then and now, the M16 (like most AR-15s ... energy of 2,267 ft-lbs with a 135 grain bullet. Instead of comparing other rifle cartridges with the underpowered 5.56/.

At the same time the oval spiral bore makes the bullet rotate ... In 1962, the rifle was authorized for military use as M16 and has been in service ever since. According to open statistics ...