M16

The **M16 rifle**, officially designated *Rifle, Caliber 5.56 mm, M16*, is a United States military adaptation of the ArmaLite AR-15 rifle. The original M16 was a select-fire, 5.56×45mm rifle with a 20-round magazine.

In 1963, the M16 entered United States Military service and was deployed for jungle warfare operations during the Vietnam War. In 1969, the M16A1 replaced the M14 rifle to become the U.S. military's standard service rifle. The M16A1 improvements include a bolt-assist, chromed plated bore and a new 30-round magazine. In 1983, the USMC adopted the M16A2 rifle and the U.S. Army adopted it in 1986. The M16A2 fires the improved 5.56×45mm NATO
 (M855/SS109) cartridge and has a new adjustable rear sight, case
deflector, heavy barrel, improved handguard, pistol grip and buttstock,
as well as a semi-auto and three-round burst only fire selector. Adopted in 1998, the M16A4 is the fourth generation of the M16 series. It is equipped with a removable carrying handle and Picatinny rail for mounting optics and other ancillary devices.The M16 has also been widely adopted by other militaries around the
world. Total worldwide production of M16s has been approximately 8
million, making it the most-produced firearm of its 5.56 mm caliber. The U.S. Army has largely replaced the M16 in combat units with the shorter and lighter M4 carbine, and the U.S. Marine Corps approved a similar change in October 2015.

## History

### Background

After World War II, the United States military started looking for a single automatic rifle to replace the M1 Garand, M1/M2 Carbines, M1918 Browning Automatic Rifle, M3 "Grease Gun" and Thompson submachine gun.[25][26] However, early experiments with select-fire versions of the M1 Garand proved disappointing. During the Korean War, the select-fire M2 Carbine largely replaced the submachine gun in US service and became the most widely used Carbine variant. However, combat experience suggested that the .30 Carbine round was under-powered. American weapons designers concluded that an intermediate round was
necessary, and recommended a small-caliber, high-velocity cartridge.

However, senior American commanders having faced fanatical enemies
and experienced major logistical problems during WWII and the Korean War, insisted that a single powerful .30 caliber cartridge be developed,
that could not only be used by the new automatic rifle, but by the new general-purpose machine gun (GPMG) in concurrent development. This culminated in the development of the 7.62×51mm NATO cartridge and the M14 rifle which was basically an improved select-fire M1 Garand with a 20-round magazine. The U.S. also adopted the M60 GPMG. Its NATO partners adopted the FN FAL and HK G3 rifles, as well as the FN MAG and Rheinmetall MG3 GPMGs.

The first confrontations between the AK-47 and the M14 came in the early part of the Vietnam War.
 Battlefield reports indicated that the M14 was uncontrollable in
full-auto and that soldiers could not carry enough ammo to maintain fire
 superiority over the AK-47.[41] And, while the M2 Carbine offered a high rate of fire, it was under-powered and ultimately outclassed by the AK-47.[42]
 A replacement was needed: A medium between the traditional preference
for high-powered rifles such as the M14, and the lightweight firepower
of the M2 Carbine.

As a result, the Army was forced to reconsider a 1957 request by
General Willard G. Wyman, commander of the U.S. Continental Army Command
 (CONARC) to develop a .223 caliber (5.56 mm) select-fire rifle weighing
 6 lb (2.7 kg) when loaded with a 20-round magazine.[25] The 5.56mm round had to penetrate a standard U.S. helmet
 at 500 yards (460 meters) and retain a velocity in excess of the speed
of sound, while matching or exceeding the wounding ability of the .30
Carbine cartridge.[43]

This request ultimately resulted in the development of a scaled-down version of the Armalite AR-10, called AR-15 rifle.[10][11][44]
 However, despite overwhelming evidence that the AR-15 could bring more
firepower to bear than the M14, the Army opposed the adoption of the new
 rifle.[10]
 In January 1963, Secretary of Defense Robert McNamara concluded that
the AR-15 was the superior weapon system and ordered a halt to M14
production.[10]
 At the time, the AR-15 was the only rifle available that could fulfill
the requirement of a universal infantry weapon for issue to all
services.

After modifications (most notably, the charging handle was re-located
 from under the carrying handle like AR-10 to the rear of the receiver),[11] the new redesigned rifle was subsequently adopted as the M16 Rifle.[10][18]
 "(The M16) was much lighter compared to the M14 it replaced, ultimately
 allowing Soldiers to carry more ammunition. The air-cooled,
gas-operated, magazine-fed assault rifle was made of steel, aluminum
alloy and composite plastics, truly cutting-edge for the time. Designed
with full and semi-automatic capabilities, the weapon initially did not
respond well to wet and dirty conditions, sometimes even jamming in
combat. After a few minor modifications, the weapon gained in popularity
 among troops on the battlefield."[45][46]

### Adoption

In July 1960, General Curtis LeMay
 was impressed by a demonstration of the ArmaLite AR-15. In the summer
of 1961, General LeMay was promoted to United States Air Force, Chief of
 Staff, and requested 80,000 AR-15s. However, General Maxwell D. Taylor, Chairman of the Joint Chiefs of Staff, advised President John F. Kennedy that having *two* different calibers within the military system at the same time would be problematic and the request was rejected.[47] In October 1961, William Godel, a senior man at the Advanced Research Projects Agency, sent 10 AR-15s to South Vietnam. The reception was enthusiastic, and in 1962, another 1,000 AR-15s were sent.[48] United States Army Special Forces
 personnel filed battlefield reports lavishly praising the AR-15 and the
 stopping-power of the 5.56 mm cartridge, and pressed for its adoption.

The damage caused by the 5.56 mm bullet was originally believed to be
 caused by "tumbling" due to the slow 1 in 14-inch (360 mm) rifling
twist rate.[47]
 However, any pointed lead core bullet will "tumble" after penetration
in flesh, because the center of gravity is towards the rear of the
bullet. The large wounds observed by soldiers in Vietnam were actually
caused by bullet fragmentation, which was created by a combination of
the bullet's velocity and construction.[49] These wounds were so devastating, that the photographs remained classified into the 1980s.[50]

U.S. Secretary of Defense Robert McNamara
 now had two conflicting views: the ARPA report favoring the AR-15 and
the Army's position favoring the M14. Even President Kennedy expressed
concern, so McNamara ordered Secretary of the Army Cyrus Vance
 to test the M14, the AR-15 and the AK-47. The Army reported that only
the M14 was suitable for service, but Vance wondered about the
impartiality of those conducting the tests. He ordered the Army
Inspector General to investigate the testing methods used; the Inspector
 General confirmed that the testers were biased towards the M14.

In January 1963, Secretary McNamara received reports that M14
production was insufficient to meet the needs of the armed forces and
ordered a halt to M14 production. At the time, the AR-15 was the only
rifle that could fulfill a requirement of a "universal" infantry weapon
for issue to all services. McNamara ordered its adoption, despite
receiving reports of several deficiencies, most notably the lack of a chrome-lined barrel.[51]

After modifications (most notably, the charging handle was re-located
 from under the carrying handle like AR-10 to the rear of the receiver),[11] the new redesigned rifle was renamed the *Rifle, Caliber 5.56 mm, M16*.[10][18]
 Inexplicably, the modification to the new M16 did not include a
chrome-lined barrel. Meanwhile, the Army relented and recommended the
adoption of the M16 for jungle warfare operations. However, the Army
insisted on the inclusion of a forward assist
 to help push the bolt into battery in the event that a cartridge failed
 to seat into the chamber. The Air Force, Colt and Eugene Stoner
believed that the addition of a forward assist was an unjustified
expense. As a result, the design was split into two variants: the Air
Force's M16 without the forward assist, and the XM16E1 with the forward assist for the other service branches.

In November 1963, McNamara approved the U.S. Army's order of 85,000 XM16E1s;[52] and to appease General LeMay, the Air Force was granted an order for another 19,000 M16s.[53][54] In 1964, the Army accepted delivery of the first batch of 2129 rifles and an additional 57,240 rifles the following year.[18]

A U.S. Soldier cleans his XM16E1 during the Vietnam War in 1966.

In 1964, the Army was informed that DuPont could not mass-produce the IMR 4475 stick powder to the specifications demanded by the M16. Therefore, Olin Mathieson Company provided a high-performance ball propellant.
 While the Olin WC 846 powder achieved the desired 3,300 ft (1,000 m)
per second muzzle velocity, it produced much more fouling, that quickly
jammed the M16s action (unless the rifle was cleaned well and often).

Front cover - The M16A1 Rifle - Operation and Preventive Maintenance by Will Eisner

In March 1965, the Army began to issue the XM16E1 to infantry units.
However, the rifle was initially delivered without adequate cleaning
kits or instructions because Colt had claimed the M16 was self-cleaning.
 As a result, reports of stoppages in combat began to surface. The most
severe problem, was known as "failure to extract"—the spent cartridge
case remained lodged in the chamber after the rifle was fired.[55] Documented accounts of dead U.S. troops found next to disassembled rifles eventually led to a Congressional investigation.[56]

In February 1967, the improved XM16E1 was standardized as the M16A1.[53]
 The new rifle was given a chrome-lined barrel to eliminate corrosion
and stuck cartridges, as well as other minor modifications. New cleaning
 kits, powder solvents and lubricants were also issued. Intensive
training programs in weapons cleaning were instituted including a comic book-style operations manual.[58][59]
 As a result, reliability problems quickly diminished and the M16A1
rifle achieved widespread acceptance by U.S. troops in Vietnam.[46] However the M16 rifle continued to suffer from a reputation of unreliability for some time.[53]

In 1969, the M16A1 officially replaced the M14 rifle to become the U.S. military's standard service rifle.[16][17] In 1970, the new WC 844 powder was introduced to reduce fouling.[60]

## Reliability

During the early part of its career, the M16 had a reputation for
poor reliability and a malfunction rate of two per 1000 rounds fired.[61]
 The M16 uses a unique gas powered operating system. "This gas operating
 system works by passing high pressure propellant gasses tapped from the
 barrel down a tube and into the carrier group within the upper
receiver, and is commonly but incorrectly referred to as a "direct impingement gas system"
 system. The gas expands within a donut shaped gas cylinder within the
carrier. Because the bolt is prevented from moving forward by the
barrel, the carrier is driven to the rear by the expanding gasses and
thus converts the energy of the gas to movement of the rifle’s parts.
The bolt bears a piston head and the cavity in the bolt carrier is the
piston sleeve. It is more correct to call it an “internal piston”
system."[62]
 This design is much lighter and more compact than a gas-piston design.
However, this design requires that combustion byproducts from the
discharged cartridge be blown into the receiver as well. This
accumulating carbon and vaporized metal build-up within the receiver and
 bolt-carrier negatively affects reliability and necessitates more
intensive maintenance on the part of the individual soldier. The
channeling of gasses into the bolt carrier during operation increases
the amount of heat that is deposited in the receiver while firing the
M16 and causes essential lubricant to be "burned off". This requires
frequent and generous applications of appropriate lubricant.[25] Lack of proper lubrication is the most common source of weapon stoppages or jams.[25]

The original M16 fared poorly in the jungles of Vietnam
 and was infamous for reliability problems in the harsh environment. As a
 result, it became the target of a Congressional investigation.[63] The investigation found that:[18]

When these issues were addressed and corrected by the M16A1, the reliability problems decreased greatly.[53] According to a 1968 Department of Army report, the M16A1 rifle achieved widespread acceptance by U.S. troops in Vietnam.[46]
 "Most men armed with the M16 in Vietnam rated this rifle's performance
high, however, many men entertained some misgivings about the M16's
reliability. When asked what weapon they preferred to carry in combat,
85 percent indicated that they wanted either the M16 or its submachine
gun version, the XM177E2. (The M14 was preferred by 15 percent, while less than one percent wished to carry either the Stoner rifle, the AK-47, the carbine or a pistol.)"[46]
 In March 1970, the "President’s Blue Ribbon Defense Panel" concluded
that the issuance of the M16 saved the lives of 20,000 U.S. servicemen
during the Vietnam War, who would have otherwise died had the M14
remained in service.[64] However the M16 rifle continued to suffer from a reputation of unreliability for some time.[53]

After the introduction of the M4 Carbine, it was found that the
shorter barrel length of 14.5 inches also has a negative effect on
reliability, as the gas port is located closer to the chamber than the
gas port of the standard length M16 rifle: 7.5 inches instead of
13 inches.[65]
 This affects the M4’s timing and increases the amount of stress and
heat on the critical components, thereby reducing reliability.[65]
 In a 2002 assessment the USMC found that the M4 malfunctioned three
times more often than the M16A4 (the M4 failed 186 times for 69,000
rounds fired, while the M16A4 failed 61 times).[66] Thereafter, the Army and Colt worked to make modifications to the M4s and M16A4s in order to address the problems found.[66]
 In tests conducted in 2005 and 2006 the Army found that on average, the
 new M4s and M16s fired approximately 5,000 rounds between stoppages.[66][67]

In December 2006, the Center for Naval Analyses
 (CNA) released a report on U.S. small arms in combat. The CNA conducted
 surveys on 2,608 troops returning from combat in Iraq and Afghanistan
over the past 12 months. Only troops who fired their weapons at enemy
targets were allowed to participate. 1,188 troops were armed with M16A2
or A4 rifles, making up 46 percent of the survey. 75 percent of M16
users (891 troops) reported they were satisfied with the weapon. 60
percent (713 troops) were satisfied with handling qualities such as
handguards, size, and weight. Of the 40 percent dissatisfied, most were
with its size. Only 19 percent of M16 users (226 troops) reported a
stoppage, while 80 percent of those that experienced a stoppage said it
had little impact on their ability to clear the stoppage and re-engage
their target. Half of the M16 users never experienced failures of their
magazines to feed. 83 percent (986 troops) did not need their rifles
repaired while in theater. 71 percent (843 troops) were confident in the
 M16's reliability, defined as level of soldier confidence their weapon
will fire without malfunction, and 72 percent (855 troops) were
confident in its durability, defined as level of soldier confidence
their weapon will not break or need repair. Both factors were attributed
 to high levels of soldiers performing their own maintenance. 60 percent
 of M16 users offered recommendations for improvements. Requests
included greater bullet lethality, new-built rifles instead of rebuilt,
better quality magazines, decreased weight, and a collapsible stock.
Some users recommended shorter and lighter weapons such as M4 carbine.[68] Some issues have been addressed with the issuing of the Improved STANAG magazine in March 2009,[69][70] and the M855A1 Enhanced Performance Round in June 2010.[71]

In early 2010, two journalists from the New York Times
 spent three months with soldiers and Marines in Afghanistan. While
there, they questioned around 100 infantry troops about the reliability
of their M16 rifles, as well as the M4 carbine. The troops did not
report reliability problems with their rifles. While only 100 troops
were asked, they engaged in daily fighting in Marja, including least a dozen intense engagements in Helmand Province, where the ground is covered in fine powdered sand (called "moon dust" by troops) that can stick to firearms.[72]
 Weapons were often dusty, wet, and covered in mud. Intense firefights
lasted hours with several magazines being expended. Only one soldier
reported a jam when his M16 was covered in mud after climbing out of a
canal. The weapon was cleared and resumed firing with the next chambered
 round. Furthermore, the Marine Chief Warrant Officer responsible for
weapons training and performance of the Third Battalion, Sixth Marines,
reported that "We've had nil in the way of problems; we've had no
issues." with his battalion's 350 M16s and 700 M4s.[72]

## NATO standards

German Army soldiers of the 13th Panzergrenadier Division qualify with the M16A2 at Würzburg, as part of a partnership range with the U.S. 1st Infantry Division.

In March 1970, the U.S. recommended that all NATO forces adopt the 5.56×45mm cartridge.[73]
 This shift represented a change in the philosophy of the military's
long-held position about caliber size. By the mid 1970s, other armies
were looking at M16-style weapons. A NATO standardization effort soon
started and tests of various rounds were carried out starting in 1977.[73]
 The U.S. offered the 5.56×45mm M193 round, but there were concerns
about its penetration in the face of the wider introduction of body armor.[25] In the end the Belgian 5.56×45mm SS109 round was chosen (STANAG 4172) in October 1980.[73]
 The SS109 round was based on the U.S. cartridge but included a new
stronger, heavier, 62 grain bullet design, with better long range
performance and improved penetration (specifically, to consistently
penetrate the side of a steel helmet at 600 meters).[25] Due to its design and lower muzzle velocity (about 3110 ft/s)[74] the Belgian SS109 round is considered more humane because it is less likely to fragment than the U.S. M193 round.[75] The NATO 5.56×45mm standard ammunition produced for U.S. forces is designated M855.

In October 1980, shortly after NATO accepted the 5.56×45mm NATO rifle cartridge.[76] Draft Standardization Agreement 4179 (STANAG 4179) was proposed to allow NATO members to easily share rifle ammunition and magazines down to the individual soldier level. The magazine chosen to become the *STANAG magazine*
 was originally designed for the U.S. M16 rifle. Many NATO member
nations, but not all, subsequently developed or purchased rifles with
the ability to accept this type of magazine. However, the standard was
never ratified and remains a 'Draft STANAG'.[77]

The NATO Accessory Rail STANAG 4694, or Picatinny rail
 STANAG 2324, or a "Tactical Rail" is a bracket used on M16 type rifles
to provide a standardized mounting platform. The rail comprises a series
 of ridges with a T-shaped cross-section interspersed with flat "spacing
 slots". Scopes are mounted either by sliding them on from one end or
the other; by means of a "rail-grabber" which is clamped to the rail
with bolts, thumbscrews or levers; or onto the slots between the raised
sections. The rail was originally for scopes. However, once established,
 the use of the system was expanded to other accessories, such as
tactical lights, laser aiming modules, night vision devices, reflex sights, foregrips, bipods, and bayonets.

Currently, the M16 is in use by 15 NATO countries and more than 80 countries worldwide.

## Design

Top drawing is of an A2-style rifle; bottom drawing is of an A2-style rifle with A1 rear sights (as with the C7)

The M16 is a lightweight, 5.56 mm, air-cooled, gas-operated, magazine-fed assault rifle, with a rotating bolt. The M16's receivers are made of 7075 aluminum alloy, its barrel, bolt, and bolt carrier of steel, and its handguards, pistol grip, and buttstock of plastics.

The M16A1 was especially lightweight at 7.9 pounds (3.6 kg) with a loaded 30-round magazine.[78] This was significantly less than the M14 that it replaced at 10.7 pounds (4.9 kg) with a loaded 20-round magazine.[79] It is also lighter when compared to the AKMs 8.3 pounds (3.8 kg) with a loaded 30-round magazine.[80]

The M16A2 weighs 8.8 lb (4.0 kg) loaded with a 30-round magazine,[81]
 because of the adoption of a thicker barrel profile. The thicker barrel
 is more resistant to damage when handled roughly and is also slower to
overheat during sustained fire. Unlike a traditional "bull" barrel that
is thick its entire length, the M16A2's barrel is only thick forward of
the handguards. The barrel profile under the handguards remained the
same as the M16A1 for compatibility with the M203 grenade launcher.

### Barrel

Early model M16 barrels had a rifling
 twist of 4 grooves, right hand twist, 1 turn in 14 inches (1:355.6 mm)
bore - as it was the same rifling used by the .222 Remington sporting
round. This was shown to make the light .223 Remington bullet yaw in
flight at long ranges and it was soon replaced. Later models had an
improved rifling with 6 grooves, right hand twist, 1 turn in 12 inches
(1:304.8 mm) for increased accuracy and was optimized for use with the
standard U.S. M193 cartridge. Current models are optimized for the
heavier NATO SS109 bullet and have 6 grooves, right hand twist, 1 turn
in 7 in (1:177.8 mm).[82][83][84][85]
 Weapons designed to accept both the M193 or SS109 rounds (like civilian
 market clones) have a 6-groove, right hand twist, 1 turn in 9 inches
(1:228.6 mm) bore.

### Recoil

"The (M16's) Stoner system provides a very symmetric design that
allows straight line movement of the operating components. This allows
recoil forces to drive straight to the rear. Instead of connecting or
other mechanical parts driving the system, high pressure gas performs
this function, reducing the weight of moving parts and the rifle as a
whole."[62] The M16's straight-line recoil design, where the recoil spring is located in the stock directly behind the action,[86] and serves the dual function of operating spring and recoil buffer.[86]
 The stock being in line with the bore also reduces muzzle rise,
especially during automatic fire. Because recoil does not significantly
shift the point of aim, faster follow-up shots are possible and user
fatigue is reduced. Also, current model M16 flash-suppressors also act
as compensators to reduce recoil further.[87]

 **energy** | 3.2 ft-lbs

Notes: Free Recoil is mathematical equation calculated by using the rifle weight, bullet weight, muzzle velocity and charge weight.[88] It is that which would be measured if the rifle were fired suspended from strings, free to recoil.[88] As mentioned above, a rifles perceived recoil is also dependent on many other factors which are not readily quantified.[88]

### Sights

The M16's most distinctive ergonomic feature is the carrying handle
and rear sight assembly on top of the receiver. This is a by-product of
the original design, where the carry handle served to protect the
charging handle.[86] As the line of sight is 2.5 in (63.5 mm) over the bore, the M16 has an inherent parallax
 problem. At closer ranges (typically inside 15–20 meters), the shooter
must aim high in order to place shots where desired. The M16 has a
500 mm (19.75 inches) sight radius.[89] The M16 uses an L-type flip, aperture rear sight and it is adjustable with two settings, 0 to 300 meters and 300 to 400 meters.[90]
 The front sight is a post adjustable for elevation in the field. The
rear sight can be adjusted in the field for windage. The sights can be
adjusted with a bullet tip and soldiers are trained to zero their own
rifles. The sight picture is the same as the M14, M1 Garand, M1 Carbine
and the M1917 Enfield. The M16 also has a "Low Light Level Sight
System", which includes a front sight post with a small glass vial of
(glow-in-the-dark) radioactive Tritium H3 and a larger aperture rear
sight.[91]
 The M16 can also mount a scope on the carrying handle. With the advent
of the M16A2, a new fully adjustable rear sight was added, allowing the
rear sight to be dialed in for specific range settings between 300 and
800 meters and to allow windage adjustments without the need of a tool
or cartridge.[92] Modern versions such as M16A4 use Picatinny rails,
 which allows the use of various scopes and sighting devices. The
current United States Army and Air Force issue M4 Carbine comes with the
 M68 Close Combat Optic and Back-up Iron Sight.[93][94] The United States Marine Corps uses the ACOG Rifle Combat Optic[95][96] and the United States Navy uses EOTech Holographic Weapon Sight.[97]

### Range and accuracy

weight
weight
@ 100 meters
 M16
(11.9 g)
[98]
(3.6 g)
[99]
(990 m/s)
[99]
(1,764 j)
[99]
(460 m)
[90]
(650 m)
[98]
(900 m)
[98]
(2700 m)
[98]
(11 cm)
[98]
(32 cm)
[100]

Note \*: The effective range of a firearm is the maximum
distance at which a weapon may be expected to be accurate and achieve
the desired effect.[101]

Note \*\*: The horizontal range is the distance traveled by a bullet,
fired from the rifle at a height of 1.6 meters and 0° elevation, until
the bullet hits the ground.[102]

Note \*\*\*: The lethal range is the maximum range of a small-arms
projectile, while still maintaining the minimum energy required to put a
 man out of action, which is generally believed to be 15 kilogram-meters
 (108 ft.-Ibs.).[98] This is the equivalent of the muzzle energy of a .22LR handgun.[103]

Note \*\*\*\*: The maximum range of a small-arms projectile is attained at
about 30° elevation. This maximum range is only of safety interest, not
for combat firing.[98]

The M16 has always enjoyed a reputation for excellent accuracy.[104][105] Its light recoil, high-velocity and flat trajectory allow shooters to take head shots out to 300 meters.[104][106] Newer M16s use the newer M855 cartridge increasing their effective range to 600 meters.[107] They are also more accurate than their predecessors and are capable of shooting 1–3 inch groups at 100 yards.[108][109] "In Fallujah, Marines with ACOG-equipped
 M16A4s created a stir by taking so many head shots that until the
wounds were closely examined, some observers thought the insurgents had
been executed."[110]
 The newest M855A1 EPR cartridge is even more accurate and during
testing "...has shown that, on average, 95 percent of the rounds will
hit within an 8 x 8-inch target at 600 meters."[111]
NATO E-type Silhouette Target

### Terminal ballistics

The 5.56×45mm cartridge had several advantages over the 7.62×51mm NATO round used in the M14 rifle. It enabled each soldier to carry more ammunition and was easier to control during automatic or burst fire.[113]
 The 5.56×45mm NATO cartridge can also produce massive wounding effects
when the bullet impacts at high speed and yaws ("tumbles") in tissue
leading to fragmentation and rapid transfer of energy.[114][115][116]

@ 10 meters
@ 100 meters
@ 100 meters
(one center rib)
(14 gauge)
@ 100 meters
(8 gauge)
+ layers of
 M16
(bullet fragments
into smaller pieces)
[117][118]
(complete bullet
disintegration)
[119]
(bullet tumbled)
[119]
[119]
one side to 500 m
[119]
[119]
[120]

Wound profiles in ballistic gelatin
Note: images are not to same scale

M16 M193 5.56×45mm

M16A2 SS109/M855 5.56×45mm NATO

The original ammunition for the M16 was the 55-grain M193 cartridge.
When fired from a 20" barrel at ranges of up to 100 meters, the
thin-jacketed lead-cored round traveled fast enough (above 2900 ft/s)
that the force of striking a human body would cause the round to yaw (or
 tumble) and fragment into about a dozen pieces of various sizes thus
created wounds that were out of proportion to its caliber.[117][118] These wounds were so devastating that many considered the M16 to be an inhumane weapon.[75][121][122] As the 5.56mm round's velocity decreases, so does the number of fragments that it produces.[25]
 The 5.56mm round does not normally fragment at distances beyond 200
meters or at velocities below 2500 ft/s, and its lethality becomes
largely dependent on shot placement.[25][118]

With the development of the M16A2, the new 62-grain M855 cartridge
was adopted in 1983. The heavier bullet had more energy, and was made
with a steel core to penetrate Soviet body armor.
 However, this caused less fragmentation on impact and reduced effects
against targets without armor, both of which lessened kinetic energy
transfer and wounding ability.[55]
 Some soldiers and Marines coped with this through training, with
requirements to shoot vital areas three times to guarantee killing the
target.[123]

However, there have been repeated and consistent reports of the
M855's inability to wound effectively (i.e. fragment) when fired from
the short barreled M4 carbine (even at close ranges).[25] The M4's 14.5" barrel length reduces muzzle velocity to about 2900 ft/s.[124]
 This reduced wounding ability is one reason that, despite the Army's
transition to short-barrel M4's, the Marine Corps has decided to
continue using the M16A4 with its 20″ barrel as the 5.56×45mm M855 is
largely dependent upon high velocity in order to wound effectively.[25]

In 2003, the U.S. Army contended that the lack of lethality of the 5.56×45mm was more a matter of perception than fact.[125][126] With good shot placement to the head and chest, the target was usually defeated without issue.[125][127] The majority of failures were the result of hitting the target in non-vital areas such as extremities.[125] However, a minority of failures occurred in spite of multiple hits to the chest.[125] In 2006, a study found that 20% of soldiers using the M4 Carbine wanted more lethality or stopping power.[128]
 In June 2010, the United States Army announced it began shipping its
new 5.56mm, lead-free, M855A1 Enhanced Performance Round to active
combat zones.[129]
 This upgrade is designed to maximize performance of the 5.56×45mm
round, to extend range, improve accuracy, increase penetration and to
consistently fragment in soft-tissue when fired from not only standard
length M16s, but also the short-barreled M4 carbines.[111][129][130] The U.S. Army has been so impressed with the new M855A1 EPR round that they're now developing a 7.62 NATO variant.[131][132]

### Magazines

Vietnam era 20-round magazine (left) and Current issue NATO STANAG 30-round magazine (right)

The M16's magazine was meant to be a lightweight, disposable item.[133][134] As such, it is made of pressed/stamped aluminum and was not designed to be durable.[133]
 The M16 originally used a 20-round magazine which was later replaced by
 a bent 30-round design. As a result, the magazine follower tends to
rock or tilt, causing malfunctions.[134]
 Many non-U.S. and commercial magazines have been developed to
effectively mitigate these shortcomings (e.g., H&K's
all-stainless-steel magazine, Magpul's polymer P-MAG, etc.).[133][134]

Production of 30-round magazine started late 1967 but did not fully replace the 20-round magazine till the mid 1970s.[134] Standard USGI aluminum 30-round M16 magazines weigh 0.24 lb (0.11 kg) empty and are 7.1 inches (18 cm) long.[135][136] The newer plastic magazines are about a half inch longer.[137] And, the newer steel magazines are about 0.5 inch longer and 4 ounces heavier.[138] The M16s magazine has become the unofficial NATO STANAG magazine and is currently used by many Western Nations, in numerous weapon systems.[139][140]

In 2009, the U.S. Military began fielding an "improved magazine" identified by a tan-colored follower.[141][142]
 "The new follower incorporates an extended rear leg and modified bullet
 protrusion for improved round stacking and orientation. The
self-leveling/anti-tilt follower minimizes jamming while a wider spring
coil profile creates even force distribution. The performance gains have
 not added weight or cost to the magazines."[142]

### Muzzle devices

Most M16 rifles have a barrel threaded in 1⁄2-28" threads to incorporate the use of a muzzle device such as a flash suppressor or sound suppressor.[143]
 The initial flash suppressor design had three tines or prongs and was
designed to preserve the shooter's night vision by disrupting the flash.
 Unfortunately it was prone to breakage and getting entangled in
vegetation. The design was later changed to close the end to avoid this
and became known as the "A1" or "bird cage" flash suppressor on the
M16A1. Eventually on the M16A2 version of the rifle, the bottom port was
 closed to reduce muzzle climb and prevent dust from rising when the
rifle was fired in the prone position.[144] For these reasons, the U.S. military declared the A2 flash suppressor as a compensator or a muzzle brake; but it is more commonly known as the "GI" or "A2" flash suppressor.[113]

The M16's Vortex Flash Hider weighs 3 ounces, is 2.25 inches long, and does not require a lock washer to attach to barrel.[145]
 It was developed in 1984, and is one of the earliest privately designed
 muzzle devices. The U.S. military uses the Vortex Flash Hider on M4 carbines and M16 rifles.[146][147] A version of the Vortex has been adopted by the Canadian Military for the Colt Canada C8 CQB rifle.[148]
 Other flash suppressors developed for the M16 include the Phantom Flash
 Suppressor by Yankee Hill Machine (YHM) and the KX-3 by Noveske
Rifleworks.[149]

The threaded barrel allows sound suppressors with the same thread
pattern to be installed directly to the barrel; however this can result
in complications such as being unable to remove the suppressor from the
barrel due to repeated firing on full auto or three-round burst.[150] A number of suppressor manufacturers such as Advanced Armament Corporation, Gemtech, Smith Enterprise, SureFire
 and OPS Inc. have turned to designing "direct-connect" sound
suppressors which can be installed over an existing M16's flash
suppressor as opposed to using the barrel's threads.[150]

### Grenade launchers and shotguns

Loading an M203 40 mm grenade launcher attached to an M16 rifle with a practice round.

All current M16 type rifles are designed to fire STANAG (NATO standard) 22 mm rifle grenades
 from their integral flash hiders without the use of an adapter. These
22 mm grenade types range from anti-tank rounds to simple finned tubes
with a fragmentation hand grenade attached to the end. They come in the
"standard" type which are propelled by a blank cartridge inserted into
the chamber of the rifle. They also come in the "bullet trap" and "shoot
 through" types, as their names imply, they use live ammunition. The
U.S. military does not generally use rifle grenades; however, they are
used by other nations.[151]

All current M16 type rifles can mount under-barrel 40 mm grenade-launchers, such as the M203 and M320. Both use the same 40 mm grenades as the older, stand-alone M79 grenade launcher. The M16 can also mount under-barrel 12 gauge shotguns such as KAC Masterkey or the M26 Modular Accessory Shotgun System.

### Riot Control Launcher

M234 Riot Control Launcher

USMC M16A2s with the OKC-3S bayonet.

The M234 Riot Control Launcher is an M16-series rifle attachment firing an M755 blank round.
 The M234 mounts on the muzzle, bayonet lug and front sight post of the
M16. It fires either the M734 64 mm Kinetic Riot Control or the M742
64 mm CSI Riot Control Ring Airfoil Projectiles. The latter produces a 4
 to 5 foot tear gas cloud on impact. The main advantage to using Ring Airfoil Projectiles is that their design does not allow them be thrown back by rioters with any real effect. The M234 is no longer used by United States forces. It has been replaced by the M203 40mm grenade launcher and nonlethal ammunition.

### Bayonet

The M16 is 44.25 inches (1124mm) long with an M7 bayonet attached.[90] The M7 bayonet is based on earlier designs such as the M4, M5, & M6 bayonets, all of which are direct descendants of the M3 Fighting Knife and have spear-point blade with a half sharpened secondary edge. The newer M9 bayonet
 has a clip-point blade with saw teeth along the spine, and can be used
as a multi-purpose knife and wire-cutter when combined with its
scabbard. The current USMC OKC-3S bayonet bears a resemblance to the Marines' iconic Ka-Bar fighting knife with serrations near the handle.

### Bipod

The M16 and M16A1 were able to use the XM3 bipod. The XM3 bipod was a
 lightweight non-adjustable support that clamped onto the barrel of the
M16 rifle for more accurate firing. The design did not see full scale
use and was scrapped shortly after the Vietnam War.

## Variants

For more details on M16 variants, see AR-15 variants.

### Pre-Production ArmaLite AR-15

The weapon that eventually became the M16 series was basically a scaled down AR-10 with an ambidextrous charging handle located within the carrying handle, a narrower front sight "A" frame, and no flash suppressor.[152]

### AR-15 (Colt Models 601 & 602)

Main article: AR-15

Colt's first two models produced after the acquisition of the rifle
from ArmaLite were the 601 and 602, and these rifles were in many ways
clones of the original ArmaLite rifle (in fact, these rifles were often
found stamped *Colt ArmaLite AR-15, Property of the U.S. Government caliber .223*, with no reference to them being M16s).[153]
 The 601 and 602 are easily identified by their flat lower receivers
without raised surfaces around the magazine well and occasionally green
or brown furniture. The 601 was adopted first of any of the rifles by
the USAF, and was quickly supplemented with the XM16 (Colt Model 602)
and later the M16 (Colt Model 604) as improvements were made. There was
also a limited purchase of 602s, and a number of both of these rifles
found their way to a number of Special Operations units then operating
in South East Asia, most notably the U.S. Navy SEALs.
 The only major difference between the 601 and 602 is the switch from
the original 1:14-inch rifling twist to the more common 1:12-inch twist.
 These weapons were equipped with a triangular charging handle and a
bolt hold open device that lacked a raised lower engagement surface. The
 bolt hold open device had a slanted and serrated surface that had to be
 engaged with a bare thumb, index finger, or thumb nail because of the
lack of this surface.
The United States Air Force continued to use the AR-15 marked rifles in various configurations into the 1990s.

### M16

Variant originally adopted by the U.S. Air Force. This was the first
M16 adopted operationally. This variant had triangular handguards, butt
stocks without a compartment for the storage of a cleaning kit,[154] a three-pronged flash suppressor, and no forward assist.
 Bolt carriers were originally chrome plated and slick-sided, lacking
forward assist notches. Later, the chrome plated carriers were dropped
in favor of Army issued notched and parkerized
 carriers though the interior portion of the bolt carrier is still
chrome-lined. The Air Force continued to operate these weapons until
around 2001, at which time the Air Force converted all of its M16s to
the M16A2 configuration.

The M16 was also adopted by the British SAS, who used it during the Falklands War.[155]

### XM16E1 and M16A1 (Colt Model 603)

An early M16 rifle: note "duckbill" flash suppressor, triangular grip, forward assist, and the lack of brass deflector

The U.S. Army XM16E1 was essentially the same weapon as the M16 with the addition of a forward assist and corresponding notches in the bolt carrier. The M16A1 was the finalized production model in 1967.

To address issues raised by the XM16E1's testing cycle, a closed,
bird-cage flash suppressor replaced the XM16E1's three-pronged flash
suppressor which caught on twigs and leaves. Various other changes were
made after numerous problems in the field. Cleaning kits were developed
and issued while barrels with chrome-plated chambers and later fully
lined bores were introduced.

With these and other changes, the malfunction rate slowly declined
and new soldiers were generally unfamiliar with early problems. A rib
was built into the side of the receiver on the XM16E1 to help prevent
accidentally pressing the magazine release button while closing the
ejection port cover. This rib was later extended on production M16A1s to
 help in preventing the magazine release from inadvertently being
pressed. The hole in the bolt that accepts the cam pin was crimped
inward on one side, in such a way that the cam pin may not be inserted
with the bolt installed backwards, which would cause failures to eject
until corrected. The M16A1 is no longer in service with the United
States, but is still standard issue in many world armies.

### M16A2

M16A2

New rear sight, brass deflector and forward assist of M16A2

A U.S Marine with an M16A2 on a training exercise at Camp Baharia, Iraq, 2004

The development of the M16A2 rifle was originally requested by the United States Marine Corps
 as a result of the USMC's combat experience in Vietnam with the XM16E1
and M16A1. It was officially adopted by US Department of Defense as the
"US Rifle, 5.56mm, M16A2" in 1982. The Marines were the first branch of
the U.S. Armed Forces to adopt the M16A2 in the early/mid-1980s, with
the United States Army
 following suit in the late 1980s. Modifications to the M16A2 were
extensive. In addition to the new rifling, the barrel was made with a
greater thickness in front of the front sight post, to resist bending in
 the field and to allow a longer period of sustained fire without
overheating. The rest of the barrel was maintained at the original
thickness to enable the M203 grenade launcher
 to be attached. A new adjustable rear sight was added, allowing the
rear sight to be dialed in for specific range settings between 300 and
800 meters to take full advantage of the ballistic characteristics of
the new SS109 rounds and to allow windage adjustments without the need
of a tool or cartridge.[156]
 The weapon's reliability allowed it to be widely used around the United
 States Marine Corps special operations divisions as well. The flash
suppressor was again modified, this time to be closed on the bottom so
it would not kick up dirt or snow when being fired from the prone
position, and acting as a recoil compensator.[157]
 The front grip was modified from the original triangular shape to a
round one, which better fit smaller hands and could be fitted to older
models of the M16. The new handguards were also symmetrical so that
armories need not separate left and right spares. The handguard
retention ring was tapered to make it easier to install and uninstall
the handguards. A notch for the middle finger was added to the pistol
grip, as well as more texture to enhance the grip. The buttstock was
lengthened by 5⁄8 in (15.9 mm).[158]
 The new buttstock became ten times stronger than the original due to
advances in polymer technology since the early 1960s. Original M16
stocks were made from fiberglass-impregnated resin; the newer stocks
were engineered from DuPont Zytel glass-filled thermoset polymers. The
new stock included a fully textured polymer buttplate for better grip on
 the shoulder, and retained a panel for accessing a small compartment
inside the stock, often used for storing a basic cleaning kit. The
heavier bullet reduces muzzle velocity from 3,200 feet per second (980 m/s), to about 3,050 feet per second (930 m/s).[159]
 The A2 uses a faster twist rifling to allow the use of a
trajectory-matched tracer round. It has a 1:7 twist rate. A spent case
deflector was incorporated into the upper receiver immediately behind
the ejection port to prevent cases from striking left-handed users.[92]

The action was also modified, replacing the fully automatic setting with a three-round burst setting.[156]
 When using a fully automatic weapon, inexperienced troops often hold
down the trigger and "spray" when under fire. The U.S. Army concluded
that three-shot groups provide an optimum combination of ammunition
conservation, accuracy, and firepower.[160]
 The USMC has retired the M16A2 in favour of the newer M16A4, although a
 few M16A2s are still in use by the United States Marine Corps today.
Many M16A2s remain in service with the U.S. Army, Air Force, Navy and
Coast Guard.[*citation needed*]

### M16A3

The M16A3 is a select-fire variant of the M16A2 adopted in small
numbers around the time of the introduction of the M16A2, primarily by
the U.S. Navy for use by SEAL, Seabee, and Security units.[161] It features the M16A1 trigger group providing "safe", "semi-automatic", and "fully automatic" modes.

### M16A4

United States Marine Corps M16A4 rifle with Picatinny rail and foregrip.

The M16A4 is the fourth generation of the M16 series. It is equipped with a removable carrying handle and a full length quad Picatinny rail
 for mounting optics and other ancillary devices. The FN M16A4, using
safe/semi/burst selective fire, became standard issue for the U.S.
Marine Corps and is the current issue to Marine Corps recruits in both
MCRD San Diego and MCRD Parris Island.[161]

Military issue rifles are also equipped with a Knight's Armament Company
 M5 RAS hand guard, allowing vertical grips, lasers, tactical lights,
and other accessories to be attached, coining the designation M16A4 MWS
(or Modular Weapon System) in U.S. Army field manuals.[162]

Colt also produces M16A4 models for international purchases, with specifics selective fire:

* R0901 / NSN 1005-01-383-2872 (Safe/Semi/Auto)
* R0905 (Safe/Semi/Burst)

A study of significant changes to Marine M16A4 rifles released in
February 2015 outlined several new features that could be added from
inexpensive and available components. Those features included: a muzzle
compensator in place of the flash suppressor to manage recoil and allow
for faster follow-on shots, though at the cost of noise and flash
signature and potential overpressure in close quarters; a heavier and/or
 free-floating barrel to increase accuracy from 4.5 MOA to potentially 2 MOA; changing the reticle on the Rifle Combat Optic from chevron-shaped to the semi-circle with a dot at the center used in the M27 IAR's
 Squad Day Optic so as not to obscure the target at long distance; using
 a trigger group with a more consistent pull force, even a
reconsideration of the burst capability; and the addition of
ambidextrous charging handles and bolt catch releases for easier use
with left-handed shooters.[163]

In 2014, Marine units were provided with a limited number of
adjustable stocks in place of the traditional fixed stock for their
M16A4s to issue to smaller Marines that would have trouble comfortably
reaching the trigger when wearing body armor. The adjustable stocks were
 added as a standard authorized accessory, meaning units can use
operations and maintenance funds to purchase more if needed.[164]

The Marine Corps had long maintained the full-length M16 as their
standard infantry rifle, but in October 2015 the switch to the M4
carbine was approved as the standard-issue weapon, giving Marine
infantrymen a smaller and more compact weapon. Enough M4s are already in
 the inventory to re-equip all necessary units by September 2016, and
M16A4s will be moved to support[24][165] and non-infantry Marines.[166]

## Derivatives

### Colt Model 655 and 656 "Sniper" variants

With the expanding Vietnam War,
 Colt developed two rifles of the M16 pattern for evaluation as possible
 light sniper or designated marksman rifles. The Colt Model 655 M16A1
Special High Profile was essentially a standard A1 rifle with a heavier
barrel and a scope bracket that attached to the rifle's carry handle.
The Colt Model 656 M16A1 Special Low Profile had a special upper
receiver with no carrying handle. Instead, it had a low-profile iron
sight adjustable for windage and a Weaver base for mounting a scope, a
precursor to the Colt and Picatinny rails. It also had a hooded front
iron sight in addition to the heavy barrel. Both rifles came standard
with either a Leatherwood/Realist scope 3–9× Adjustable Ranging
Telescope. Some of them were fitted with a Sionics noise and flash
suppressor. Neither of these rifles were ever standardized.

These weapons can be seen in many ways to be predecessors of the U.S. Army's SDM-R and the USMC's SAM-R weapons.

### XM177

Main article: CAR-15

A United States Air Force GAU-5/A carbine

In Vietnam, some soldiers were issued a carbine version of the M16 called the XM177.
 The XM177 had a shorter 10 in (254 mm) barrel and a telescoping stock,
which made it substantially more compact. It also possessed a
combination flash hider/sound moderator to reduce problems with muzzle
flash and loud report. The Air Force's GAU-5/A (XM177) and the Army's
XM177E1 variants differed over the latter’s inclusion of a forward
assist, although some GAU-5s do have the forward assist. The final Air
Force GAU-5/A and Army XM177E2 had an 11.5 in (292 mm) barrel with a
longer flash/sound suppressor. The lengthening of the barrel was to
support the attachment of Colt's own XM148
 40 mm grenade launcher. These versions were also known as the Colt
Commando model commonly referenced and marketed as the CAR-15. The
variants were issued in limited numbers to special forces, helicopter
crews, Air Force pilots, Air Force Security Police Military Working Dog
(MWD) handlers, officers, radio operators, artillerymen, and troops
other than front line riflemen. Some USAF GAU-5A/As were later equipped
with even longer 14.5-inch (370 mm) 1/12 rifled barrels as the two
shorter versions were worn out. The 14.5-inch (370 mm) barrel allowed
the use of MILES gear and for bayonets to be used with the sub-machine
guns (as the Air Force described them). By 1989, the Air Force started
to replace the earlier barrels with 1/7 rifled models for use with the
M855-round. The weapons were given the redesignation of GUU-5/P.
These were effectively used by the British Special Air Service during the Falklands War.[155]

### Colt Model 733

Colt also returned to the original "Commando" idea, with its Model 733, essentially a modernized XM177E2 with many of the features introduced on the M16A2.

### M231 Firing Port Weapon (FPW)

M231 FPW

M231 Firing Port Weapon (FPW) is an adapted version of the M16 assault rifle for firing from ports on the M2 Bradley.
 The infantry's normal M16s are too long for use in a "buttoned up"
fighting vehicle, so the FPW was developed to provide a suitable weapon
for this role. Designed by the Rock Island Arsenal, the M231 FPW remains
 in service, although all but the rear two firing ports on the Bradley
have been removed. The M231 FPW fires from the open bolt and is only
configured for fully automatic fire. The open bolt configuration gives
the M231 a much higher cyclic rate of fire than the closed bolt
operation of the M16A1. Official doctrine discourages deploying M231
outside of the firing port role. The weapon jams easily and is known to
break the bolt without warning.

### Mk 4 Mod 0

The Mk 4 Mod 0 was a variant of the M16A1 produced for the U.S. Navy
SEALs during the Vietnam War and adopted in April 1970. It differed from
 the basic M16A1 primarily in being optimized for maritime operations
and coming equipped with a sound suppressor. Most of the operating parts
 of the rifle were coated in Kal-Guard,
 a hole of 0.25 inches (6.4 mm) was drilled through the stock and buffer
 tube for drainage, and an O-ring was added to the end of the buffer
assembly. The weapon could reportedly be carried to the depth of 200
feet (60 m) in water without damage. The initial Mk 2 Mod 0 Blast
Suppressor was based on the U.S. Army's Human Engineering Lab's (HEL) M4
 noise suppressor. The HEL M4 vented gas directly from the action,
requiring a modified bolt carrier. A gas deflector was added to the
charging handle to prevent gas from contacting the user. Thus, the HEL
M4 suppressor was permanently mounted though it allowed normal
semi-automatic and automatic operation. If the HEL M4 suppressor were
removed, the weapon would have to be manually loaded after each single
shot. On the other hand, the Mk 2 Mod 0 blast suppressor was considered
an integral part of the Mk 4 Mod 0 rifle, but it would function normally
 if the suppressor were removed. The Mk 2 Mod 0 blast suppressor also
drained water much more quickly and did not require any modification to
the bolt carrier or to the charging handle. In the late 1970s, the Mk 2
Mod 0 blast suppressor was replaced by the Mk 2 blast suppressor made by
 Knight's Armament Company (KAC). The KAC suppressor can be fully
submerged and water will drain out in less than eight seconds. It will
operate without degradation even if the rifle is fired at the maximum
rate of fire. The U.S. Army replaced the HEL M4 with the much simpler
Studies in Operational Negation of Insurgency and Counter-Subversion
(SIONICS) MAW-A1 noise and flash suppressor.

### Mark 12

Main article: United States Navy Mark 12 Mod X Special Purpose Rifle

Developed to increase the effective range of soldiers in the
designated marksman role, the U.S. Navy developed the Mark 12 Special
Purpose Rifle (SPR). Configurations in service vary, but the core of the
 Mark 12 SPR is an 18" heavy barrel with muzzle brake and free float
tube. This tube relieves pressure on the barrel caused by standard
handguards and greatly increases the potential accuracy of the system.
Also common are higher magnification optics ranging from the 6× power
Trijicon ACOG to the Leupold Mark 4 Tactical rifle scopes. Firing Mark
262 Mod 0 ammunition with a 77gr Open tip Match bullet, the system has
an official effective range of 600+ meters. However published reports of
 confirmed kills beyond 800 m from Iraq and Afghanistan are not
uncommon.[*citation needed*]

### M4 carbine

Main article: M4 carbine

An M4A1 carbine (foreground) and two M16A2s (background) being fired by U.S. Marines during a live fire exercise: though adopted in the 1990s and derived from the M16A2, the M4 carbine was part of a long line of short-barreled AR-15 used in the U.S. military

The M4 carbine was developed from various outgrowths of these
designs, including a number of 14.5-inch (368 mm)-barreled A1 style
carbines. The XM4 (Colt Model 727) started its trials in the mid-1980s,
with a barrel of 14.5 inches (370 mm). Officially adopted as a
replacement for the M3 "Grease Gun" (and the Beretta M9
 and M16A2 for select troops) in 1994, it was used with great success in
 the Balkans and in more recent conflicts, including the Afghanistan and Iraq theaters. The M4 carbine has a three-round burst firing mode, while the M4A1 carbine has a fully automatic firing mode. Both have a Picatinny rail on the upper receiver, allowing the carry handle/rear sight assembly to be replaced with other sighting devices.

### Heckler & Koch HK416

Main article: Heckler & Koch HK416

The **Heckler & Koch HK416** is an assault rifle designed and manufactured by Heckler & Koch. It is based on the M16 platform, and was originally conceived as an improvement based on the Colt M4 carbine
 family issued to the U.S. military, with the notable inclusion of an
HK-proprietary short-stroke gas piston system derived from the Heckler & Koch G36. The HK416 was used by United States Navy SEALs to kill Osama bin Laden.[167][168]

### Diemaco C7 and C8

Main article: Colt Canada C7 rifle

Canadian Forces Reserve infantrymen train in urban operations with C7 and C8 rifles.

The Diemaco C7 and C8 are updated variants of the M16 developed and used by the Canadian Forces and are now manufactured by Colt Canada.
 The C7 is a further development of the experimental M16A1E1. Like
earlier M16s, it can be fired in either single shot or automatic mode,
instead of the burst function selected for the M16A2. The C7 also
features the structural strengthening, improved handguards, and longer
stock developed for the M16A2. Diemaco changed the trapdoor in the
buttstock to make it easier to access and a spacer of 0.5 inches (13 mm)
 is available to adjust stock length to user preference. The most easily
 noticeable external difference between American M16A2s and Diemaco C7s
is the retention of the A1 style rear sights. Not easily apparent is
Diemaco's use of hammer-forged barrels. The Canadians originally desired
 to use a heavy barrel profile instead.
The C7 has been developed to the C7A1, with a Weaver rail
 on the upper receiver for a C79 optical sight, and to the C7A2, with
different furniture and internal improvements. The Diemaco produced
Weaver rail on the original C7A1 variants does not meet the M1913
'Picatinny' standard, leading to some problems with mounting commercial
sights. This is easily remedied with minor modification to the upper
receiver or the sight itself. Since Diemaco's acquisition by Colt to
form Colt Canada, all Canadian produced flattop upper receivers are
machined to the M1913 standard.

The C8 is the carbine version of the C7.[169] The C7 and C8 are also used by *Hærens Jegerkommando*, *Marinejegerkommandoen* and FSK (Norway), Military of Denmark (all branches), the Royal Netherlands Army and Netherlands Marine Corps as its main infantry weapon. Following trials, variants became the weapon of choice of the British SAS.

☀Type
Assault rifle
Place of origin
United States
Service history
In service
1962–present
Used by
See *Users*

Wars
Vietnam War
Laotian Civil War
Cambodian Civil War
The Troubles
Cambodian–Vietnamese War
1982 Lebanon War
Invasion of Grenada
South Lebanon conflict (1985–2000)
Nepalese civil war
Bougainville Civil War[1]
United States invasion of Panama
Oka Crisis[2]
Gulf War
Somali Civil War
Yugoslav Wars
Operation Deny Flight
Operation Joint Endeavor
War in Afghanistan
Iraq War
Syrian Civil War
Gaza–Israel conflict
2014 pro-Russian unrest in Ukraine
Iraq War (2014–present)[3]
Several other conflicts
Production history
Designer
Eugene Stoner and L. James Sullivan[4]

Designed
1956[5]

Manufacturer

* Colt's Manufacturing Company
* Daewoo Precision Industries
* FN Herstal
* H&R Firearms
* General Motors Hydramatic Division
* Elisco
* U.S. Ordnance

Produced
1959–present[5]

Number built
~8 million[6]

Variants
See *Variants*

Specifications (M16)
Weight
7.18 lb (3.26 kg) (unloaded)

8.79 lb (3.99 kg) (loaded)
Length
39.5 in (1,003 mm)
Barrel length
20 in (508 mm)

Cartridge
5.56×45mm NATO
Action
Gas-operated, rotating bolt (direct impingement)
Rate of fire
12–15 rounds/min sustained
45–60 rounds/min semi-automatic
700–950 rounds/min cyclic
Muzzle velocity
3,110 ft/s (948 m/s)[7]

Effective firing range
550 m (601 yd) (point target)[8]
800 m (875 yd) (area target)[9]

Maximum firing range
3,600 m (3,937 yd)
Feed system
20-round detachable box magazine:
0.211 lb (96 g) empty / 0.738 lb (335 g) full)
30-round detachable box magazine:
0.257 lb (117 g) empty / 1.06 lb (480 g) full)
Beta C-Mag 100-round double-lobed drum:
2.20 lb (1,000 g) empty / 4.81 lb (2,180 g) full)
Sights
Iron sights