The AR-15 is the semiautomatic version of the M16 series of assault rifles, designed by the great designer Eugene Stoner, and it is most commonly used by the US armed forces. I would get into the history of this gun, but it is very longwinded but thoroughly interesting. AR-15s are usually chambered in 5.56 x 45mm (.223 Remington) caliber and have either 24", 20", 16", or 11.5" barrels and have either collapsible stocks or full stocks and may either have a NATO railed flattop or a carrt handle with an adjustable rear sight. This weapon has been the basis of numerous high-accuracy rifles.
I am so getting an AR-15 when I get my license.
An assault rifle most commonly used by Law Enforcement and Military. The AR15 uses the .223 Caliber (NATO 5.56).
During the North Hollywood shoot-out between the two gunmen armed with AK-47s and Body Armour. The LAPD had no tactical advantage against the two gunmen with their puny ass 9mm pistols. They went to a local gunshop and snagged some AR15s and shot the gunmen down since their body armour couldn't stop it.