"The main functional difference between the military’s M16 and M4 rifles and a civilian AR-15 is the "burst" mode on many military models, which allow three rounds to be fired with one trigger pull. Some military versions of the rifles have a full automatic feature, which fires until the trigger is released or a magazine is empty of ammunition. But in actual American combat these technical differences are less significant than they seem. For decades the American military has trained its conventional troops to fire their M4s and M16s in the semiautomatic mode — one bullet per trigger pull — instead of on “burst” or automatic in almost all shooting situations. The weapons are more accurate this way, and thus more lethal. The National Rifle Association and other pro-gun groups highlight the fully automatic feature in military M4s and M16s. But the American military, after a long experience with fully automatic M16s reaching back to Vietnam, decided by the 1980s to issue M16s, and later M4s, to most conventional troops without the fully automatic function, and to train them to fire in a more controlled fashion. What all of this means is that the Parkland gunman, in practical terms, had the same rifle firepower as an American grunt using a standard infantry rifle in the standard way... A New York Times analysis of a video from a Florida classroom estimates that during his crime the gunman fired his AR-15 as quickly as one-and-a-half rounds per second. The military trains soldiers to fire at a sustained rate of 12 to 15 rounds per minute, or a round every four or five seconds."