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Carbine, 5.56 mm, M4
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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 made by ArmaLite. It is a shorter and lighter version of the M16A2 assault rifle, achieving 80% parts commonality with the M16A2. The M4 has selective fire options including semi-automatic and three-round burst (like the M16A2), while the M4A1 has a "full auto" option in place of the three-round burst.

OverviewEdit

The M4 and variants fire 5.56x45mm 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 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.

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. 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 has an exclusive contract to produce the M4 family of weapons through 2009; however, a number of other manufacturers offer M4-like firearms. The M4A1, along with the M16A4, have mostly replaced the M16A2; the U.S. Air Force, for example, plans to transition completely to the M4. The M4 is also the standard rifle for U.S. Air Force Security Forces members whether at home station or deployed abroad. They maintain a yearly qualification on it.

The United States Marine Corps has ordered its officers (up to the rank of lieutenant colonel) and Staff Non-commissioned officers to carry the M4A1 carbine instead of the M9 handgun. This is in keeping with the Marine Corps motto, "Every Marine a rifleman." United States Navy corpsmen will also be issued M4A1s instead of the M9.

History and variantsEdit

Except for the very first delivery order, all U.S. military-issue M4 and M4A1 possess a flat-top NATO M1913-specification (Picatinny) rail on top of the receiver for attachment of optical sights and other aiming devices — Trijicon TA01 and TA31 Advanced Combat Optical Gunsights (ACOG), EOTech 550 series holographic sights, and Aimpoint M68 Close Combat Optic (M68 CCO) being the favorite choices — and a detachable rail-mounted carrying handle. Standards are the Colt Model 920 (M4) and 921 (M4A1).

Variants of the carbine built by different manufacturers are also in service with many other foreign special forces units, such as the Australian Special Air Service Regiment (SASR). While the SASR uses weapons of essentially the same pattern built by Colt for export (Colt uses different models to separate weapons for the U.S. military and those for commercial/export purposes), the British SAS uses a variant on the basic theme, the Colt Canada (formerly Diemaco) C8SFW.

M4A1Edit

The M4A1 carbine is a fully-automatic variant of the basic M4 carbine intended for special operations use. The M4A1 has a "S-1-F" (safe/semi-automatic/fully automatic) trigger group, while the M4 has a "S-1-3" (safe/semi-automatic/3-round burst) trigger group. The M4A1 is used by almost all U.S special operation units. The M4A1 is especially favored by counter-terrorist and special forces units for close quarters combat because of the carbine's compactness and firepower. These features are also very useful in urban warfare. Although the M4 has less effective range than the longer M16, many military analysts consider engagement with a non-specialized small arm above a range of 300 meters (330 yd) to be unnecessary. It is effective at ranges of 150 meters (160 yd) or less and has a maximum effective range of about 500 to 600 meters (550–660 yd).

In the last few years, M4A1 carbines have been refit or received straight from factory with barrels with a thicker profile under the handguard. This is for a variety of reasons such as heat dissipation, which is useful due to the complaints of high-heat production from test soldiers, which occurs during full-auto and accuracy as a byproduct of barrel weight. These heavier barrel weapons are also fitted with a heavier buffer known as the H2. Out of three sliding weights inside the buffer, the H2 possesses two tungsten weights and one steel weight, versus the standard H buffer, which uses one tungsten weight and two steel weights. These weapons, known by Colt as the Model 921HB (for Heavy Barrel), have also been designated M4A1, and as far as the government is concerned the M4A1 represents both the 921 and 921HB.

SOPMOD Block IEdit

USSOCOM developed the Special Operations Peculiar Modification (SOPMOD) Block I kit for the carbines used by units under its jurisdiction. The kit features an M4A1, a Rail Interface System (RIS) handguard developed by Knight's Armament Company, a shortened quick-detachable M203 grenade launcher and leaf sight, a KAC sound suppressor, a KAC back-up rear sight, an Insight Technologies AN/PEQ-2A visible laser/infrared designator, along with Trijicon's ACOG and Reflex sights, and a night vision sight. This kit was designed to be configurable (modular) for various missions, and the kit is currently in service with special operations units.

SOPMOD Block IIEdit

A second-generation SOPMOD kit (now known as SOPMOD II) is currently under development, with many different manufacturers competing for the contract. Notable bidders include Knight's Armament Company, Atlantic Research Marketing Systems (ARMS), and Lewis Machine & Tools. Daniel Defense has won the contract for the RIS-II, the next generation of rail handguards.

DesignEdit

The M4/M4A1 5.56mm 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 14.5 in (368 mm) 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 has semi-automatic and three-round burst fire modes, while the M4A1 has "semi" and "full auto", with no three-round burst. The M4 has over 80% commonality with the M16A2 rifle and 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 M4 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 of rifle.

  • 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.

AccessoriesEdit

Like all the variants of the M16, the M4 and the M4A1 can be fitted with many accessories, such as night vision devices, suppressors, laser pointers, telescopic sights, bipods, either the M203 or M320 grenade launchers, the M26 MASS shotgun, and anything else compatible with a MIL-STD-1913 Picatinny rail.

Other common accessories include the AN/PEQ-2, Advanced Combat Optical Gunsight (ACOG), and M68 CCO. EOTech holographic weapon sights are part of the SOPMOD II package. Visible and IR (infrared) lights of various manufacturers are also commonly attached using various mounting methods. As with all versions of the M16, the M4 accepts a blank-firing attachment (BFA).

EffectivenessEdit

An April 2002 presentation by the US Army Natick Soldier Center presented by LTC Charlie Dean and SFC Sam Newland reported on lessons learned from M4 use in Afghanistan (such as use during Operation Anaconda):

  • 90% of soldiers reported confidence in the weapon.
  • 20% were dissatisfied with its ease of maintenance.
  • 34% of soldiers reported that their M4's handguards rattled and became excessively hot when firing.
  • 15% reported that they had trouble zeroing the M68 reflex sight.
  • 35% added barber brushes and 24% added dental picks to their cleaning kits.

Soldiers reported the following malfunctions:

  • 20% reported double-feeding.
  • 15% reported feeding jams.
  • 13% reported that feeding problems were usually due to magazines.

Soldiers requested the following changes:

  • 55% requested the firearm be made lighter.
  • 20% requested a slightly larger magazine.

2007 dust testEdit

In the fall of 2007, the Army tested the M4 against three other carbines in "sandstorm conditions" at Aberdeen Proving Ground, Maryland: the Heckler & Koch XM8 rifle, Fabrique Nationale de Herstal SOF Combat Assault Rifle (SCAR) and the Heckler & Koch HK416. Ten of each type of rifle were used to fire 6,000 rounds each, for a total of 60,000 rounds per rifle type.[8] The M4 suffered far more stoppages than its competitors: 882 stoppages, 19 requiring an armorer to fix. The XM8 had the fewest stoppages, 116 minor stoppages and 11 major ones, followed by the FN SCAR with 226 stoppages and the HK416 with 233.[9][10] The Army was quick to point out that even with 863 minor stoppages—termed "class one" stoppages which require 10 seconds or less to clear and "class two" stoppages which require more than ten seconds to clear—the M4 functioned well, with over 98 percent of the 60,000 total rounds firing without a problem. The Army said it planned to improve the M4 with a new cold-hammer-forged barrel to give longer life and more reliable magazines to reduce the stoppages. Magazine failures caused 239 of the M4's 882 failures. Army officials said the new magazines could be combat-ready by spring if testing went well.

UsersEdit

  • Afghanistan: Only used by Afghan Army commandos. M4s sold as part of a 2006 Foreign Military Sales package. Additional M4s sold as a 2008 Foreign Military Sales package.
  • Australia: Used by Special Operations Command.
  • Bangladesh: Used by Bangladesh Paracommandos,Dhaka Metropolitan Police SWAT teams and Special Warfare Diving And Salvage[20]
  • Bahrain: M4A1s sold as a 2008 Foreign Military Sales package.
  • Belize: M4s/M4A1s sold as part of a 2006 Foreign Military Sales package.
  • Brazil: M4A1s used by Grupo de Ações Táticas Especiais and Batalhão de Operações Policiais Especiais.
  • Canada: Used by JTF2 and other various police departments. Not to be confused with the Canadian designed and made C8 carbine
  • Colombia: M4A1s as part of a 2008 Foreign Military Sales.
  • Ecuador: M4s sold as a 2008 Foreign Military Sales package.
  • El Salvador: M4s sold as part of a 2007 Foreign Military Sales package. Additional M4s sold as a 2008 Foreign Military Sales package.
  • Georgia: M4A1 and M4A3. Police Special Forces, Armed Forces, mainly regular army and Special Forces
  • India: M4A1s as part of a 2008 Foreign Military Sales.
  • Indonesia: Used by Detachment 88 operators.
  • Iraq: Used by the Iraqi Army.[25] Main weapon of the Iraqi National Counter-Terrorism Force.
  • Israel: Sold as part of a January 2001 Foreign Military Sales package to Israel.
  • Jamaica: M4s sold as part of a 2007 Foreign Military Sales package.
  • Japan: M4A1s as part of a 2008 Foreign Military Sales package. M4A1 SOPMOD rifles are in use by the Japanese Special Operations Group.
  • Jordan: M4s sold as part of a 2007 Foreign Military Sales package. Additionals M4s sold as a 2008 Foreign Military Sales package.
  • Lebanon: M4 components being sold to Lebanese special forces. M4/M4A1s sold as a 2008 Foreign Military Sales package.
  • Macedonia: M4s sold as a 2008 Foreign Military Sales package.
  • Malaysia: Licensed by SME Ordnance Sdn Bhd. To be used by the Malaysian Armed Forces, special forces of Malaysian Maritime Enforcement Agency and Royal Malaysian Police.
  • Nepal: Sold as part of a 2005 Foreign Military Sales package.
  • New Zealand: Used by NZSAS operators.
  • Panama: M4A1s sold as a 2008 Foreign Military Sales package.
  • Philippines: M4/M4A1s sold as a 2008 Foreign Military Sales package.
  • Thailand: M4A1s sold as part of a 2006 Foreign Military Sales package.
  • Tonga: M4/M4A1s sold as a 2008 Foreign Military Sales package.
  • United Arab Emirates: Purchased 2,500 M4 carbines in 1993.
  • Yemen: M4s sold as part of a 2006 Foreign Military Sales package.