Not according to the military-- which has a description for everything with which they fool. The M-16 with its 20" barrel and triangular handguard is what soldiers took to Vietnam in the 1960s and early 1970s. The M4 with its 14.5" barrel and round handguards is the carbine version of the M-16. The lower receiver of either is more or less identical because the function of each firearm is identical, save for the M-16 being full-auto and the M4 being three-round burst-fire. But you knew all that...Wait; those aren't the same?