The military version of the Armalite AR-15 built by Eugene Stoner from his AR-10 was designated M-16 and first deployed in Vietnam in 1963. This one (top) is the M16A2E2 with retractable stock and Picatinny rail foregrip. Over 8 million M16s have been produced of which 90% are still in use and they are still the main rifle for US forces, although the US Army will eventually replace them with M4s.
They are in use by 15 NATO countries and more than 80 countries world wide.
The M4 is a carbine of the M16A2 (with 80% of parts in common) which is shorter, lighter and more suited to close quarter combat. It also has a versatile rail system as standard and is already in use in over 40 countries. There are many civilian versions of M4s (known as M4geries) and many variants.
This version (bottom) is a Close Quarter Battle (CQB) version, about 4 inches shorter than the standard M4A1, with a holographic sight.
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