In the Marines, most units have the M-14 A-4, but there are still some M-16 A-2 rifles in some units. They also use M-4, which is a shorter version of the M-16. They also have a M-9, which is a 9mm pistol. Some carry a M-249, which is commonly refferred to as a SAW (squad automatic weapon). I do not think there is a such thing as a M-16 A3. The Army uses the same equipment. They usually get the newer equipment first. They probably do not use the M-16 A-2 rifles as much as the Marines.