M4 Carbine: A world’s most popular special operations forces rifle

Operators with an M4A1 SOPMOD Block II in Afghanistan in 2012
Operators with an M4A1 SOPMOD Block II in Afghanistan in 2012 (Photo: XY)

The M4 Carbine is one of the most popular rifles, and for many special operations forces operators, a first pick. It belongs to 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 has been in service for more than 25 years.


The M4 is a shorter and lighter version of the Colt M16A2 assault rifle, with 80% parts commonality. The rifle has selective fire options including semi-automatic and three-round burst (like the M16A2) while the M4A1 has a “full auto” option along with three-round burst.

M16A2 US soldier on shooting range
U.S. soldier shooting from M16A2 assault rifle (Photo: XY)


The M4 and its variants are chambered in 5.56×45 mm NATO ammunition (or .223 Remington ammunition). The M4 is a gas-operated, air-cooled, magazine-fed, selective fire rifle with a multi-position telescoping stock. The first versions of the carbine 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.

In comparison, the M4 is similar to earlier 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 main advantage of the M4 is its operability because it is handier and more convenient than a full-length assault rifle. It doesn’t affect so much ballistic performance of the rifle if compared to the full-size M16 (6″ longer barrel). This becomes most apparent at ranges of 300 yards and beyond.

An M4A1 rifle with upgraded SOPMOD Block II kit
An M4A1 rifle with upgraded SOPMOD Block II kit (Photo: XY)

But, in fact, if we look from the point of the statistic, the most small-arms engagements occur within 100 yards. This means that the M4 Carbine is very much an adequate weapon for the majority of troops, and especially modern special operations forces and their usage in the counter-terrorism missions. 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 Carbine′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) and close-quarters combat (CQC). 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 M4A1, along with the M16A4, have mostly replaced the Colt 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 is a rifleman.” United States Navy corpsmen will also be issued M4A1s instead of the M9.


The M4 doesn’t have so many variants especially designed because it is considered the most modular and accessible weapon platform in the world right now. Here is the list of considerable variants:

  • M4A1
  • XM177E2
  • M4 MWS (Modular Weapon System)
  • Mk 18 CQBR
  • Enhanced M4
  • M4 Commando
  • Armwest LLC M4


The M4A1 carbine is a fully-automatic variant of the basic M4 carbine intended for special operations use. The main difference between the M4A1 and “regular” Mr is in modes of fire. The M4A1 has an “S-1-3-F” (safe/semi-automatic/3-round burst/fully automatic) trigger group while the M4 has an “S-1-3″ (safe/semi-automatic/3-round burst) trigger group.

Today, the M4A1 is issued to almost all U.S special operation units. The M4A1 is especially favored by counter-terrorist and special forces units for close-quarters combat (CQC) because of the carbine’s compactness and firepower. In fact, to make it clear, carbines have shorter barrels than assault rifles, this means they do worse at the range but are easier to use in small rooms and in urban warfare.

The M4A1 has an effective range of 150 meters (160 yds) or less and has a maximum effective range of about 500 to 600 meters (550–660 yd).



USSOCOM developed the Special Operations Peculiar Modification (SOPMOD) Block I kit for the carbines used by units under its jurisdiction. It brings the M4 Carbine to a whole new level. The SOPMOD Block I kit includes:

  • M4A1 rifle
  • Rail Interface System (RIS) handguard developed by Knight’s Armament Company
  • shortened quick-detachable M203 grenade launcher
  • leaf sight
  • KAC sound suppressor
  • KAC back-up rear sight
  • Insight Technologies AN/PEQ-2A visible laser/infrared designator
  • Trijicon’s ACOG and Reflex sights
  • 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.

M4 SOPMOD Block 1
M4 SOPMOD Block 1 (Photo: XY)


A second-generation SOPMOD kit (now known as SOPMOD II) had many different manufacturers competing for the contract. The new SOPMOD Block II includes innovative optics, such as the Elcan Specter DR, Trijicon’s ACOG TA01 ECOS model, and the EOTech 553. Block II uses the RIS II rails manufactured by Daniel Defense in both a 9.5 and 12.5-inch length.

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.

US Special Forces M4 SOPMOD
US Special Forces M4A1 SOPMOD Block II (Photo: XY)

Difference between M4A1 vs M4 Carbine

There are some slight differences between these two rifles, but in the end, it is only in small improvements. Here is the list of the major improvements and differences between M4A1 and M4 rifle:

  • M4A1 has Full auto that replaces the M4’s 3 round burst
  • M4A1 has an ambidextrous safety
  • M4A1 has a heavier barrel than the M4
  • M4A1 is the Army’s new standard carbine issued to all units, infantry and combat arms taking precedents

Technical specifications: M4 Carbine

Manufacturer:Colt’s Manufacturing Company LLCP.O. Box 1868, Hartford, United States
Type:gas-operated, selective fire, rotating bolt, carbine
Caliber: 5.56 mm (.223 in)
Barrel:14.5 in (368 mm)
Weight (empty):6.63 lbs (3.01 kg)
Effective firing range:500 m
Rate of fire:700–950 rounds per min
Magazine capacity:30-round box magazine or other STANAG magazines. Magazines with different capacities are also available.
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