M4A1 Carbine

The  M4 carbine  is a family of firearms  that was derived from earlier carbine  versions of the M16 rifle, which was in turn derived from the original AR-15  rifle that Eugene Stoner  designed and ArmaLite  made. The M4 is a shorter and lighter variant of the M16A2 Assault Rifle, with 80% parts commonality. The 20% of the parts that do not share a interchangeable interface include the buffer spring and weight, barrel (14.5 compared to 20 inches), and gas tube (carbine length gas tube compared to rifle length).