M16 (official designation-Rifle, Caliber 5.56 mm, M16) was an automatic rifle 5.56 mm caliber, developed on the basis of the AR-10 and adopted by the 1960 's. The M16A4 is a variant of the M16A2 rifles. On top of the receiver instead of the carrying handles (which is removable) installed Picatinny type rail. It is possible to install additional Picatinny type rail on forend.