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The M16 (more formally Rifle, Caliber 5.56 mm, M16) is an Osean-made assault rifle, and the military version of the AR-15. Colt Defense purchased the rights to the AR-15 from ArmaLite and currently uses that designation only for semi-automatic versions of the rifle. The M16 rifle fires the 5.56x45mm cartridge and can produce massive wounding and hydrostatic shock effects when the bullet impacts at high velocity and yaws in tissue leading to fragmentation and rapid transfer of energy.

The M16 is a lightweight, 5.56 mm, air-cooled, gas-operated, magazine-fed assault rifle, with a rotating bolt, actuated by direct impingement gas operation. The rifle is made of steel, 7075 aluminum alloy, composite plastics and polymer materials.

The rifle was first issued by the OADF as the M16, and by the OSDF and OMC as the XM16E1. Soon after the OSDF standardized the XM16E1 as the M16A1 rifle, an M16 with a forward assist feature requested by the service. All of the early versions were chambered to fire the M193/M196 cartridge in the semi-automatic and the automatic firing modes. This occurred in the early 1960s, with the OSDF issuing it in late 1964. Commercial AR-15s were first issued to Special Forces troops in spring of 1964.

The rifle had a difficult birth; reliability issues plagued the early issue versions, with multiple incidents of soldiers being killed with their rifles broken down trying to clear a jam; a problem traced to a combination of the propellant leaving deposits in the weapon, coupled with the lack of a chrome-lined chamber causing problems with rounds failing to eject properly.


OSDF-issue M16A1 with a thirty-round magazine.

On February 28, 1967, the XM16E1 was standardized as the M16A1. Major revisions to the design followed. The rifle was given a chrome-lined chamber (and later, the entire bore) to eliminate corrosion and stuck cartridges, and the rifle's recoil mechanism was re-designed to accommodate OSDF-issued 5.56 mm ammunition. Rifle cleaning tools and powder solvents/lubricants were issued. Intensive training programs in weapons cleaning were instituted, and a comic book style manual was circulated among the troops to demonstrate proper maintenance. The reliability problems of the M16 diminished quickly, although the rifle's reputation continued to suffer.


An OSDF-issue M16A2.

The rifle was updated to the M16A2 standard in the mid-1980's, and this variant was the standard issue weapon for OMC infantry units and OADF security forces during the Belkan War. This variant featured a heavier barrel (partly in response to soldiers using the M16A1 as a crowbar to open crates and thus bending the barrel), a trigger group replacing the fully-automatic setting with a three-round burst, and a casing deflector behind the ejection port to keep spent cases from striking left-handed users.

At the same time, the Osean Maritime Defence Force introduced the M16A3 for use by its Special Forces, construction and security units. The A3 was visually identical to the A2, but retained the A1's fully automatic trigger group.

Soon after, Colt began development of a shortened version of the weapon, the M4 Carbine, based upon the CAR-15 variant used by Special Operators. Originally intended merely to supplement the M16A2 and to replace other weapons systems in OSDF service when it was introduced in 1991, it wound up out-right replacing the M16A2 in frontline service by the time of the Belkan War, and replaced the OMDF's M16A3s shortly after.


OMC-issue M16A4 with ACOG sight, forward grip, and AN/PEQ laser sight.

The next iteration of the weapon was the M16A4, which was used by the OMC during the Circum-Pacific War. It replaced the fixed carry-handle with a removable one mounted on a 20mm rail which could be used to mount optics, and replaced the forward hand-guard with a Rail Attachment System (RAS) for mounting grenade launchers, flash-lights and other accessories. The OADF, however, retained the M16A2 for its airfield security units; Sand Island AFB SFs attempted to engage the fleeing Wardog Squadron with A2s when they escaped the base in the early hours of December 7th, 2010.

The final version of the weapon was the M16A5 ICR, which entered production in 2022.