The M4 and variants fire 5.56 x 45 mm NATO ammunition and are gas-operated, air-cooled, magazine-fed, selective fire firearms with a 4-position telescoping 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 and the end has a curvature. A fixed stock can also be fitted, but this is not a common practice in the U.S. military.

The M4 Carbine with the newer, redesigned telescoping stock.

As with many carbines, the M4 is handy and more convenient to carry than a full-length rifle. While this makes it a candidate for non-infantry troops (vehicle crews, clerks and staff officers), it also makes it ideal for close quarters combat (CQC), and airborne and special operations. It has been adopted by United States Special Operations Command (USSOCOM) and is the preferred weapon of the U.S. Army Special Forces. Malaysia purchased M4 Carbine service rifles to replace the Steyr AUG service rifles in its armed forces in 2006.

The M4 was developed and produced for the United States government by Colt Firearms, which has 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, has mostly replaced M16 and M16A2 firearms; the U.S. Air Force, for example, plans to transition completely to the M4 Carbine. The M4 has also replaced the M3A1 submachine gun that remained in service (mostly with tank crews). The M4 is similar to much earlier compact M16 versions, such as the 1960s-era XM177 family, though unlike them it is not intended to fire the earlier M193/6 ball ammunition.

The United States Marine Corps has ordered its officers (up to the rank of lieutenant colonel) and NCOs to carry the M4A1 carbine variant instead of the M9 Beretta pistol. This is in recognition that pistols are largely useless in current conflicts, and is in line with the Marine Corps phrase, "Every Marine a rifleman." United States Navy corpsmen will also be issued M4A1s instead of the M9, according to the Marine Corps Times.

Type Carbine

Place of origin United States of America

Service history

In service 1994¡§Cpresent

Used by United States of America and numerous others

Wars War in Afghanistan (2001¡§Cpresent), 2003 Invasion of Iraq

Production history

Produced 1994¡§Cpresent

Variants M4A1, CQBR

Specifications

Weight 2.52 kg (5.56 lb) empty;

3.0 kg (6.6 lb) w/ 30 rounds

Length 757 mm (29.8 in) (stock retracted)

838 mm (33 in) (stock extended)

Barrel length 368.3 mm (14.5 in)

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Cartridge 5.56 x 45 mm NATO

Caliber 5.56 mm (.223 in)

Action Gas-operated, rotating bolt

Rate of fire 700¡§C950 round/min

Muzzle velocity 905 m/s (2,970 ft/s)

Feed system Various STANAG Magazines.

Design

M4 with M203A1 and M68 Close Combat Optic

The M4/M4A1 5.56 mm Carbine is a gas-operated, air-cooled, magazine-fed, selective fire, shoulder-fired weapon with a telescoping stock. A shortened variant of the M16A2 rifle with a 36 cm barrel, the M4 provides the individual soldier operating in close quarters the capability to engage targets at extended range with accurate, lethal fire. The original M4 Carbine has semi-automatic and three-round burst fire modes, while the M4A1 has "semi" and "full auto", with no three-round burst. The M4 Carbine achieves over 80% commonality with the M16A2 rifle and was intended to replace the M3 .45 ACP 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 cancelled.) The M4 Carbine is also capable of mounting the M203 grenade launcher.

Some features compared to a full-length M16A2 rifle include:

• Compact size
• Shorter barrel
• Telescoping buttstock
• Selective fully automatic rather than 3-round bursts (M4A1 only)

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.