The M16 rifle and the M4 carbine are semi-automatic and automatic weapons that originated in the U.S. They are issued to U.S. troops and North Atlantic Treaty Organization (NATO) forces worldwide. The M16 was the standard U.S. military forces weapon from the mid-1960s and onward, but is being replaced by the M4, a smaller, more versatile carbine. The M16 competes with the AK-47 in worldwide sales, and the M4 is expected to be sold more globally well before 2020.

Comparison chart

M16 Rifle versus M4 Carbine comparison chart
Edit this comparison chartM16 RifleM4 Carbine
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M16 RifleM4 Carbine
Type Assault rifle Carbine
Cartridge 5.56×45mm NATO 5.56×45mm NATO
Action Gas-operated, rotating bolt (direct impingement) Gas-operated, rotating bolt
Manufacturer Colt Defense, Daewoo, FN Herstal, H & R Firearms, General Motors, Hydramatic Division, Elisco, U.S. Ordnance Colt Defense
Variants AR-15, M16A1, M16A2, M16A3, M16A4, XM16E1, M4, Mk12 M4A1, CQBR (Mk. 18 Mod 0)
Place of origin United States United States
Sights Iron or various optics Iron or various optics
Length 39.5 in (1,000 mm) 33 in (840 mm) (stock extended), 29.75 in (756 mm) (stock retracted)
Barrel Length 20 in (508 mm) 14.5 in (370 mm)
Muzzle velocity 3,110 ft/s (948 m/s) 2900 ft/sec (884 m/sec)
Weight 7.18 lbs (3.26 kg) (unloaded), 8.79 lb (4.0 kg) (loaded) 6.36 lb (2.88 kg) empty, 6.9 lb (3.1 kg) with 30 rounds
Wars Vietnam War, Invasion of Grenada, Gulf War, Somali Civil War, Operation Deny Flight, Operation Joint Endeavor, Iraq War, War in Afghanistan (2001–present) War in Afghanistan (2001–present), War in Iraq (2003–2010), Colombian Armed Conflict, Operation Enduring Freedom, 2008 South Ossetia war
Rate of Fire 700–950 rounds/min cyclic 700–950 round/min cyclic
In service 1963–present 1994–present
Feed system 20 or 30 round box magazine, Drum, Snail or other STANAG Magazines 30 round box magazine or other STANAG Magazines.
Effective range 460 meters (point target), 800 meters (area target) 500 m for a point target and 600 m for an area target


The M16 was designed in 1956 and replaced the M14 as the U.S. military's standard service rifle in 1969. forces in the Korean War. The emergence of the Russian AK-47 forced a redesign of the M14 to increase firepower and dependability, resulting in the adoption of the M16 during the Vietnam War. Development of the M16 required several iterations because of bullet design, firing modes, and structural reliability.

The M4 came about when the U.S. Pentagon began a competition to replace the M16 Rifle with a carbine design using a shorter barrel for close-quarter combat. Although M16 variants with shorter barrels were in widespread use, they were noisy, difficult to handle, and had poor accuracy. After several designs were presented, the Army took over the M4 Carbine development in 2009 and suggested changes in materials and firing action, replacing the impingement mode (like the M16) with a solely gas-operated mode. The M4 has been in widespread use by tactical forces in Afghanistan and Iraq and is scheduled to fully replace the M16 as standard issue by 2018.


The M16 was designed as an assault rifle aimed at maximum firepower. The gas-operated direct impingement system uses a rotating bolt to strike a smaller caliber bullet (5.56x45mm) than what was used in the M14, allowing for higher magazine loads (more bullets) and faster rounds. The recoil was designed to be straight-line, for easier "stay on target" action. M16s could be switched from single-fire to semi-automatic and automatic modes, with several variants used by different branches and Special Forces.

The M4's design was based on shortening the barrel length without compromising long-range accuracy, faster firing action, capability of setting a three-shot pattern, and basic versatility for additional equipment (flash suppressors, silencer, grenade launchers, etc.). All factors were geared for close combat and what the Pentagon describes as "fluid tactical situations."

About 80% of the M4 is based on M16 parts, making these weapons somewhat interchangeable and reducing new manufacturing costs. Although the cartridge remains the same between the two, the jacketing and powder mix have been modified to increase firing speed and impact profile. Barrel length can be modified with an extendable stock. At present, other modifications to the M4 design are still in progress, responding to both current needs and anticipated future needs of the U.S. and NATO forces.


The 5.56x45mm cartridge developed for the M16 gave it a better range and higher accuracy than the larger-caliber bullet used in the M14 and [[AK-47 vs AR-15|AK-47. Its size gave it higher velocity with minimal recoil and created a flatter trajectory that improved accuracy.

The M4 uses the same cartridge, modified for greater impact at higher speeds. The modification is in response to current tactical situations where close combat is more common than in previous engagements, with most of combat occurring in battlegrounds with shorter sightlines (e.g., urban and mountain terrains). There was also greater need for suppressive power, basically the capacity to shoot faster with more accuracy, which the M4's design has tried to meet.

Barrel and Range

The M16 has a standard barrel length of 39 inches (1 meter). At that length, it provides greater accuracy than the M14 or AK-47; however, the barrel is too long for close combat efficiency. Cut-down M16 barrels lose accuracy and create more flash, so a shorter carbine variant was needed to address current battlefield realities. The maximum range of an M16 is about 3,000 yards (2,700 meters), with an effective range of up to 500 yards (460 meters). Horizontal range is 711 yards (650 m) and the lethal range is 984 yards (900 m).

The M4 barrel measures 33 inches (840 mm) with the stock extended and just 29.75 inches (756 mm) with the stock retracted. The smaller barrel length allows for greater control in close quarters, not only for mobility, but also for firing. The barrel is easily interchangeable, a general design feature of the M4 aimed at making the weapon more versatile and easier to maintain in the field. The effective range of an M4 carbine is about 550 yards (500 m).

Action Type

The M16 is a rotating bolt rifle with a gas-operated direct impingement firing action. The M4 is similar, but it does not use impingement for its firing action. In this, it hews more closely to the AK-47 design in order to provide a more reliable firing action in field conditions.


The M16 magazine is lightweight compared to that of other assault rifles. It is manufactured from stamped (or mold-pressed) aluminum and is weaker structurally than most other weapons' magazines, leading to more frequent failure. M16s hold 20 or 30 bullets each and can be replaced quickly, though anyone who will use the rifle will need training for some time to master the replacement process.

The M4 magazine is sturdier to reduce in-field failure rates when dealing with sub-optimal conditions and possibly frequent impacts with the ground or structures as soldiers advance or take cover. It holds 30 bullets and is somewhat easier to switch out than the M16's, but it does require some basic training for mastery.


The basic M16 weighs between 7 and 9 pounds (3.26 to 4.0 kg), though accessories such as suppressors, scopes, and grenade launchers can practically double that weight. The basic weight for the M4 is between 6 and 7 pounds (2.9 to 3.10 kg), and the accessories weigh less as well. Most of the weight lost in the M4 is related to the barrel and stock, not to the metal-based parts that make up the firing mechanisms.


One advantage the M16 has is that the selector switch is easily reached and set without needing to take eyes off of a target. This lets the user switch from semi-automatic to automatic fire and back, but the switch's small size makes it difficult to use under stressful conditions. Left-handed users of the M16 complain that the design makes it difficult for them to field-strip it for maintenance.

The M4 has greater ergonomic efficiency in terms of selector/safety switch and maintenance. The selector switch is larger and easier to set without losing sight of targets, while the breakdown components for maintenance are relatively neutral, although still somewhat more favorable to right-handed users.


The M16, like all weapon systems, started out with a reputation of being less reliable than its predecessor (the M14). Over time, most reliability issues were reduced to low-percentage events; however, the AK-47 has long been regarded as more reliable in field conditions (wet, sandy, dirty, etc.). One improvement the M16 provided was a much higher manufacturing standard that now gives the weapon a service life of 20,000 to 50,000 rounds or more, compared to other assault rifles that max out at between 8,000 and 25,000 rounds. A major factor in M16 maintenance is lubrication, for without consistent cleaning and oiling, the weapon's performance deteriorates noticeably, even in recent variants. On the upside, this is easy to manage in field conditions.

Although the M4 has not had as much extensive field use when compared to the M16 or the AK-47, it, too, showed some early reliability issues. The gas-piston system failed in several early variants, though the problem was traced to differences in manufacturing rather than intrinsic design flaws. With new iterations, the M4 quickly gained a reputation for reliability, both on the range and in field situations. Range tests now have the M4 firing at least 1,600 rounds before jamming, up from 800, while in field conditions, soldiers report almost no failures, with the ones that are reported often due to improper or overly-delayed maintenance.

Criticisms of the M4 Carbine

The Army-issued M4 has undergone over 90 design improvements over the years, which led to the upgraded M4A1 model of the carbine. The weapon still has its critics, however. As recently as 2014, Army generals and soldiers have complained about jamming and overheating in all M4 models. Robert Scales, a military analyst and retired Army major general, has cited the M4's gas impingement system as its primary drawback and has argued that the gun cannot be improved without replacing the gas impingement system altogether.[1]

In response to complaints, the Army has called for weapons manufacturers to begin producing another round of upgrades to the military-grade carbine. The M4A1+ standard seeks to improve performance and accuracy with an extended forward rail and a low-profile gas block, among other upgrades. There are no plans to scrap the gas impingement system.[2] Max Slowik, a firearms expert, has said the M4A1+ will share many characteristics with AR-15s found on the commercial market.

Slowik and others have stated that the design flaws seen in the M4 and M4A1 have been well-known for a long time, and that the M4A1+ standard is an acknowledgment of these flaws. The commercial market has been swifter to improve upon M4/M4A1 shortcomings, and so the M4A1+ military standard will feature many of the enhancements that have been available in the private market for some years now.


In 2012, the government price of every new U.S. Army M16 was $673. That same year, the estimated cost of the M4 was about $243 more per unit, meaning that the M4 upgrade would cost $916 per carbine. Current estimates of the M4 cost place it at around $1,120 per weapon.


When the Pentagon began a search for an M16 replacement, several designs were presented by manufacturers such as Colt, FN Herstel, Heckler & Koch, and Remington. Their prototypes and others were tested extensively as early as 1983, with several trials taking place up to 1994. That year, a single-source order for the Colt M4 was made, essentially closing down the competition. Although other similar weapons were still being tested around the world, the Pentagon backed Colt in what amounted to an exclusive contract.

Use of the Colt M4 began in combat conditions in 2001, but reports of frequent failures (mainly jamming) kept the overall approval rating of the weapon under 95%, at best. The early jamming issues were resolved in manufacturing, and in 2009, the Pentagon permitted other makers to begin manufacturing M4 weapons and accessories.

In 2004, Colt filed a lawsuit alleging trademark infringement on the term "M4" against Heckler & Koch and Bushmaster. Heckler & Koch settled out of court and changed their use of the term on a similar weapon, but in 2005, Bushmaster won the case as the court stated that "M4" had become a generic term.


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