M4 Carbine: Encyclopedia II - M4 Carbine - History and variants

M4 Carbine - History and variants

Except for the very first delivery order, all U.S. military issue M4 and M4A1 possess a flat-top NATO M1913-specification rail on top of the receiver (for attachment of optical sights and other aiming devices — Trijicon TA11 and TA31 ACOGs and Aimpoint M68 CCOs being the favorite choices), and a detachable rail-mounted carrying handle. The current government standards are the Colt Model 920 (M4) and 921 (M4A1). The major difference between these models is that the M4 has the "S-1-3" (safe/semi-automatic/3-round burst) fire modes, while the M4A1 has a "S-1-F" (safe/semi-automatic/fully-automatic) fire modes.

Colt Model 925 carbines were tested fitted with the KAC M4 RAS under the designation M4E2, but this designation appears to have been scrapped in favor of mounting this system to existing carbines without changing the designation. The U.S. Army Field Manual specifies for the Army that adding the Rail Accessory System (RAS) turns the weapon into the M4 MWS or Modular Weapon System.

The M4A1 carbine is a variant of the basic M4 carbine intended for Special Operations use. The M4A1 can be found in use by many U.S. military units, including the Delta Force, U.S. Navy SEALs, and the United States Marine Corps Force Reconnaissance companies. The M4A1 Carbine is specially 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 does not have as far an effective range as the longer M16, many military analysts consider engagement with a non-specialized small arm above a range of 300 m to be unnecessary. It is extremely effective at 150 m or less.

In the last few years, M4A1 carbines have been being 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 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 there the M4A1 represents both the 921 and 921HB.

USSOCOM developed the Special Operations Peculiar Modification (SOPMOD) I M4A1 Kit for the carbines used by units under its jurisdiction. The kit features an M4A1 carbine, a Rail Interface System (RIS) handguard system developed by Knight's Armament Company (KAC), a shortened quick-detachable M203 grenade launcher and leaf sight, a KAC sound suppressor, KAC back-up rear sight, an Insight Technologies AN/PEQ-2A visible laser/infrared designator, along with Trijicon Advanced Combat Optical Gunsight Reflex optics, and a night vision sight. This kit was designed to be configurable (modular) for various missions, and the kit is in service right now with Special Operations units (though many soldiers have changed the Trijicon reflex sight for M68 Aimpoint red dot sights and EOTech holographic sights).

AR-10, AR-15
M16, M16A1, M16A2, M16A3, M16A4
M4, M4A1 Carbine
Diemaco C7, C8
CAR-15
Colt Commando
Colt M231 FPW
SDM-R, SAM-R
Mark 11 'SWS'
Mark 12 'SPR'
SEAL Recon Rifle
Mark 18 'CQBR'
Ares Shrike
La France M16K

A 2nd generation SOPMOD (now known as SOPMOD II) is currently under development, with many different manufacturers competing for a contract. Notable manufacturers include Knight's Armament Company and their URX II, ARMS and their Selective Integrated Rail (SIR) system, along with Lewis Machine & Tool's Monolithic Rail Platform (MRP).

Variants of the carbine built by different manufacturers are also in service with many other foreign special forces units, Australia's Special Air Service Regiment (SASR). While the Australian 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 SFW built by Diemaco of Canada. Ironically, this distinction is now essentially redundant with the purchase of Diemaco by Colt.

As mentioned, the M4 replaced the M3A1 submachine guns that remained in U.S. service, mainly with tank crews. They had previously had M3s, but this was changed to two M4s and two M9 pistols ('Personal Defense Weapons'). This was as much to increase capability as it was change over from .45 cal, as M3A1s could be configured to fire 9 mm ammunition.

Adapted from the Wikipedia article "History and variants", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki