History

The M4 carbine is a family of firearms tracing its lineage back to earlier carbine versions of the M16, all based on the original AR-15 designed by Eugene Stoner and made by ArmaLite. It is a shorter and lighter version of the M16A2 assault rifle, with 80% parts commonality.
 
It is a gas-operated, air-cooled, magazine-fed, selective fire, shoulder-fired weapon with a telescoping stock. A shortened variant of the M16A2 rifle, the M4 has a 14.5 in (368 mm) barrel, allowing the individual soldier to better operate in close quarters. The M4 has selective fire options including semi-automatic and three-round burst (like the M16A2), while the M4A1 has the capability to fire fully automatic instead of three-round burst. The carbine is also capable of mounting an M203 grenade launcher, the M203A1 with a 9-inch barrel as opposed to the standard 12-inch barrel of the M203 used on the M16 series.
 
The M4 carbine will eventually replace the M16 rifle for most combat units in the United States Army. The winner of the Individual Carbine competition may replace the M4 carbine in U.S. Army service

The M4 was intended to replace the .45 ACP M3 submachine guns and selected M9 pistols and M16 rifle series with most Army units (this plan was thought to be changed with the development of the XM29 OICW and the XM8 carbine; however, both projects were canceled.)
 
The United States Marine Corps has ordered its officers (up to the rank of lieutenant colonel) and Staff Non-commissioned officers to carry the M4 carbine instead of the M9 handgun. This is in keeping with the Marine Corps doctrine, "Every Marine a rifleman." United States Navy corpsmen E5 and below will also be issued M4s instead of the M9.
 

 
On July 1, 2009, the U.S. Army took complete ownership of the M4 design. This will allow companies besides Colt to compete with their own M4 designs. The Army planned on fielding the last of its M4 requirement in 2010. On October 30, 2009, Army weapons officials proposed a series of changes to the M4 to Congress. Requested changes include an electronic round counter that records the number of shots fired, a heavier barrel, and replacing the direct impingement system with a gas piston system. As of September 2010 the Army has announced they will buy 12,000 M4A1s from Colt Firearms by the end of 2010 and will by early 2011 order 25,000 more M4A1s. The Army announced also to have open competition for the newly designed M4 bolt carrier and gas piston operation system, which will be fitted to the newly bought M4A1 carbines. The service branch plans to buy 12,000 of these conversion kits in early 2011. In late 2011 the Army plans to buy 65,000 more conversion kits. From there the Army will decide if it will upgrade all of its M4s.
 
 

 
The carbine variant of the XM8 rifle was canceled in 2005.
 
On November 13, 2008, the U.S. Army hosted an invitation-only Industry Day regarding a potential future replacement for the M4 carbine. Nineteen companies provided displays and briefings for military officials. The weapons displayed included the Barrett REC7 PDW, Bushmaster ACR, FN SCAR, Heckler & Koch HK416, Heckler & Koch XM8, LWRC M6A4, Robinson Arms XCR, SIG 556, as well as Colt's own improved version of the M4, the Colt ACC-M. The goal of the Industry Day was to provide officials with knowledge as to the current state of the art, which will assist the writing of a formal requirements document.
 
The possible successor to the M4 carbine in the U.S. Army is the Individual Carbine. This program is to provide a new carbine for the Army, while the USMC has decided to stay with the M4 for carbine use.
 
 

M4 with M68 Close Combat Optic and AN/PEQ-4

Colt Model 933, a variant of the M4 with a shorter 11.5-inch barrel, seen here fitted with an M68 CCO
The M4 and its variants fire 5.56x45mm NATO ammunition (and also .223 Remington ammunition) and are gas-operated, air-cooled, magazine-fed, selective fire firearms with either a multi-position telescoping stock or a fixed A2 or LE tactical stock. Original M4 models had a flat-ended telescoping stock, but newer models are now equipped with a redesigned telescoping stock that is slightly larger with curvature at the end. The M4 is similar to much earlier compact M16 versions, such as the 1960s-era XM177 family. Some of those visual designs are obvious in both weapons, however most of the similarities are not very noticeable.
 

 
The M4 with the newer, redesigned telescoping stock
As with many carbines, the M4 is handy and more convenient to carry than a full-length rifle. The price is slightly inferior ballistic performance compared to the full-size M16, with its nearly 6" (15 cm) longer barrel. This becomes most apparent at ranges of 300 yards and beyond. Statistically, however, most small-arms engagements occur within 100 yards.[citation needed] This means that the M4 is very much an adequate weapon for the majority of troops. The marginal sacrifice in terminal ballistics and range, in exchange for greatly improved handling characteristics, is usually thought to be a worthwhile compromise.
 
While the M4's maneuverability makes it a candidate for non-infantry troops (vehicle crews, clerks and staff officers), it also makes it ideal for close quarters battle (CQB). The M4 was developed and produced for the United States government by Colt Firearms, which had an exclusive contract to produce the M4 family of weapons through 2009; however, a number of other manufacturers offer M4-like firearms. The M4, along with the M16A4, have mostly replaced the M16A2 in the Army and Marines. The U.S. Air Force, for example, plans to transition completely to the M4 for security squadrons, while other armed personnel retain the M16A2. The US Navy uses M4A1s for Special Operations and by vehicle crews.
 
Some features of the M4 and M4A1 compared to a full-length M16-series rifle include:
 Compact size
 Shortened barrel 14.5 in (368 mm)
 Telescoping buttstock
 
However, there have been some criticisms of the carbine, such as lower muzzle velocities and louder report due to the shorter barrel, additional stress on parts because of the shorter gas system, and a tendency to overheat faster than the M16A2.

Singleplayer/Spec-Ops

The M4A1 makes its return in Call of Duty: Modern Warfare 3; the carbine is shown in the single player mission "Black Tuesday". The M4A1 has a new look as well; a matte black finish, a custom charging handle assist, and a different stock. Also the gun features a new design on the iron sights. As in previous installments, a foregrip is mounted by default. From pick-up icons of the M4A1 in gameplay videos of Modern Warfare 3, it is referred to as an "M4".

Multiplayer

The M4A1 is unlocked as soon as Create a Class is unlocked at Level 4. It has medium recoil and low damage, but a fast rate of fire. This means that it is more effective at close to medium range. The afore mentioned medium recoil can be partially mitigated with the Proficiency Kick, but players will still need to burst fire at long range.

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.
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