History

The M16 (officially Rifle, Caliber 5.56 mm, M16) is the United States military designation for the AR-15 rifle adapted for both semi-automatic and full-automatic fire. Colt purchased the rights to the AR-15 from ArmaLite, and currently uses that designation only for semi-automatic versions of the rifle. The M16 fires the 5.56×45mm NATO cartridge. The rifle entered United States Army service and was deployed for jungle warfare operations in South Vietnam in 1963, becoming the U.S. military's standard service rifle of the Vietnam War by 1969, replacing the M14 rifle in that role. The U.S. Army retained the M14 in CONUS, Europe, and South Korea until 1970. Since the Vietnam War, the M16 rifle family has been the primary service rifle of the U.S. armed forces.
 
The M16 has also been widely adopted by other militaries around the world. Total worldwide production of M16-style weapons since the design's inception has been approximately 8 million, making it the most-produced firearm of its caliber. As of 2010, the M16 is being phased out in the United States Army, and is being replaced by the M4 carbine, which is itself a shortened derivative of the M16A2. The M16 could be supplemented by the Individual Carbine beginning in 2014 if procurement of that new weapon is attained.

The U.S. Army XM16E1 was essentially the same weapon as the M16 with the addition of a forward assist and corresponding notches in the bolt carrier. The M16A1 was the finalized production model in 1967. To address issues raised by the XM16E1's testing cycle, a closed, bird-cage flash suppressor replaced the XM16E1's three-pronged flash suppressor which caught on twigs and leaves. Various other changes were made after numerous problems in the field. Cleaning kits were developed and issued while barrels with chrome-plated chambers and later fully lined bores were introduced.
 
With these and other changes, the malfunction rate slowly declined and new soldiers were generally unfamiliar with early problems. A rib was built into the side of the receiver on the XM16E1 to help prevent accidentally pressing the magazine release button while closing the ejection port cover. This rib was later extended on production M16A1s to help in preventing the magazine release from inadvertently being pressed. The hole in the bolt that accepts the cam pin was crimped inward on one side, in such a way that the cam pin may not be inserted with the bolt installed backwards, which would cause failures to eject until corrected. The M16A1 remains in service in limited numbers in the United States but is still standard issue in many world armies.

Singleplayer/Spec-Ops

The M16A4 was first seen in Call of Duty: Modern Warfare 3's Special Ops Trailer. It fires in three-round bursts, like in previous games. It looks more like the M16A2 variant because of the similar rails. Also, in Call of Duty: Modern Warfare 3, a rapid fire attachment is available which will augment the ROF of every burst.

Multiplayer

The M16A4 is unlocked at level 4 along with Create-A-Class, and retains its low recoil, fast reload and relatively long ranges, and can be customized with a wide range of attachments and proficiencies. Compared to the other burst rifle, the Type 95, the M16A4 is less reliable in close quarters, requiring all 3 rounds to land from a burst to kill, but is more effective at longer ranges where the Type 95's damage drops much more drastically.

Attachments

Attachments	Challenges	Icon
Reflex Sight	Get 60 kills while looking through a Red Dot Sight attached to a Assault Rifle.
Silencer	Get 15 kills with a Silencer attached to a Assault Rifle.
Grenade Launcher	Get 20 kills with a Grenade Launcher attached to a Assault Rifle.
ACOG Scope	Get 20 kills while looking through a ACOG Scope attached to a Assault Rifle.
Rapid Fire	Get 40 kills with Rapid Fire attached to a Assault Rifle.
Heartbeat Sensor	Get 40 kills with a Heartbeat Sensor attached to a Assault Rifle.
Hybrid Sights	Get 40 kills with a Hybrid Sights attached to a Assault Rifle.
Shotgun	Get 40 kills with a Shotgun attached to a Assault Rifle.
Holographic Sight	Get 40 kills while looking through a Holographic Sight attached to a Assault Rifle.
Extended Mags	Get 40 kills with Extended Mags attached to a Assault Rifle.
Thermal	Get 40 kills while looking through a Thermal attached to a Assault Rifle.

Proficiencies

Proficiency	Description	Icon
Kick	Kick Reduces recoil by 20%, allowing for steadier full-auto and faster recovery from shots.
Impact	Impact grants maximized penetration for any weapon. This is especially powerful on Assault Rifles and SMGs, as LMGs already have strong penetration, and Sniper Rifles are difficult to use for intentional walling shots.
Attachment	Allows the use of 2 Attachments. It is a solid all-around Proficiency, useful in many situations. This Proficiency is also notably useful for stealth builds, as it allows you to use a Silencer alongside any other Attachment. The Attachment Proficiency is also helpful if you are still getting comfortable with iron sights, as it allows you to take and optical Attachment and a second utility Attachment.
Focus	Reduces visual recoil by 50% when you are hit. Focus is very effective for SMGs and Shotguns. It is also helpful for ARs, as it can keep your shots on target when you enter a heads-up one-on-one firefight.
Breath	Allows you to remove the slight sway from Assault Rifles by holding your breath. Very situational, most useful with the Type 95, M16A4 or MK14 with a long-range sight fitted. Breath can be used with automatics, as well, for careful long-range burst-fired shots, though the benefit is small.
Stability	Reduces idle sway by 25%. Consider this to be an 'automatic' Breath for long-range combat. It is most useful on LMGs, as they need the enhanced accuracy for long-range shots, though ARs also benefit from it.

Challenges