M4 MWS (Modular Weapon System)
M4 MWS (Modular Weapon System) shown with various accessories including
M203 grenade launcher, RIS foregrip, removeable carry handle/rear sight assembly,
AN/PEQ-2 laser system, and several optional optics.
Colt
Model 925 carbines were tested fitted with the
Knight's Armament Corporation (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.
M4A1
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,
U.S. Army Rangers, and the
U.S. Marine Corps' Radio Reconnaissance Platoons and
Force Reconnaissance companies. The M4A1 Carbine is specially favored by
counter-terrorist and
special operations 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 great an effective range as the longer M16, many military analysts consider engagement with a non-specialized small arm above a range of 300 meters to be unnecessary. It is effective at ranges of 150 meters or less. It has a maximum effective range of about 400 meters.
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 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 I
SOPMOD (Special Operations Peculiar Modification) Block I
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 carbine, 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 (though many soldiers have changed the Trijicon
reflex sight for M68 CCO red dot sights and
EOTech holographic sights).
SOPMOD Block II
A second-generation SOPMOD kit (now known as
SOPMOD II) is currently under development, with many different manufacturers competing for a 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.
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
SFW built by
Diemaco of Canada. Although Diemaco was purchased by Colt and renamed
Colt Canada, the Diemaco names and related firearms were kept.
As mentioned, the M4 replaced the
M3A1 "Grease Gun" submachine gun that remained in U.S. service, mainly with
tank crews. They 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 to change over from
.45 ACP, as M3A1s could be configured to fire
9 mm ammunition.
