The M4A1 carbine is a rifle developed by Colt. It is the first revision of the M4 rifle. The gun is mainly designed with a new flat-top receiver cover to install a modular aiming system. In August 1994, this flat-top M4 was officially named "5.56mm caliber M4A1 carbine" (Caliber 5.56mm, M4A1). The main improvement of the M4A1 is to change the original fixed handle to the M1913 guide rail that can be installed with different sighting devices-that is, the flat-top type receiver. In addition, the shooting mode of the M4A1 is semi-automatic, three-shot and fully automatic. M4A1 has a range and lethality worth boasting about, and a high rate of fire.