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{{weapon-firearm|
|image=[[Image:Usarmy_m16a2.jpg|300px]]
|caption=An M16A2 rifle
|name=M16
|type=service rifle
|nation=United States
|era=Vietnam, modern
|platform=Individual
|target=Personnel
|date=1957
|prod_date=1960 to present
|serv_date=1960 to present
|operators=NATO
|wars=[[Vietnam War]], [[Gulf War]], [[Iraq War|Gulf War 2]]
|spec_type=Assault Rifle
|calibre=5.56 mm
|barrel=508 mm
|ammo=[[5.56 x 45 mm NATO]]
|mag=30 or 20 rounds (see [[M16 (rifle)#Design|Design]])
|action=[[Gas operated]], [[Rotating bolt]]
|rof= 750 - 900 round/min, cyclic
|muzzle_vel=975 m/s, 884 m/s (see [[M16 (rifle)#Variants|Variants]])
|range=500 m
|weight=See [[M16 (rifle)#Design|Design]]
|length=1002 mm
|variant=[[M4 Carbine]]
|num_built=Over 8 million
}}
{{AR15etc}}
'''M16''' is the U.S. Military designation for a family of rifles derived from the [[Armalite]] [[AR-15]]. It is an [[assault rifle]] which fires [[NATO]] standard [[5.56 x 45 mm NATO|5.56 mm]] [[ammunition]]. It has been the primary [[infantry]] [[rifle]] of the [[United States military]] since 1967, is in use by 15 NATO countries, and has been the most produced firearm in its caliber.
Despite some early problems, the M16 has matured into a reasonably reliable weapon system. It is primarily [[manufacturing|manufactured]] by [[Colt Firearms|Colt]] and [[Fabrique Nationale]], with variants produced by numerous countries around the world. The semiautomatic version, the [[AR-15]] is a popular recreational firearm in the United States. The M16A2 can fire in two different modes, either semi-automatic with one round fired for every pull of the trigger, or burst mode with three rounds per pull. Mode of fire is determined by using a selector switch on the side of the weapon.
The development was guided by the Army during the 1950s, which culminated in a field trial in Vietnam in the early 1960s. This lead to its official adoption in 1964 by the USAF as the M16; with some changes the Army adopted the M16A1 officially in 1967, though various intermediate versions were already being fielding during the period under experimental designations. The M16A1 version remain in service until the 1980s, when phased out by the M16A2. The M16A3 was similar to a A2 but it was capable of full auto, and the M16A4 was essentially a flat-top M16A2. Some M16A1 fitted bipods were actually replaced by the [[M249]] machine guns during the 1980s. The M16A2 and the M249 fired the specifically adopted NATO round, with a different rifling rate than the earlier M16 and M16A1. In the 1990s many M16s were replaced with the M16 derived [[M4 Carbine]].
==History==
===Project SALVO===
In 1948, the Army organized the civilian Operations Research Office (ORO), mirroring similar [[operations research]] organizations in Britain. One of their first efforts, Project ALCLAD, studied [[body armor]] and quickly concluded that they would need to know considerably more about battlefield injuries in order to make reasonable suggestions. Over 3 million battlefield reports from WWII were analyzed, and over the next few years they released a series of reports on their findings.
Their basic conclusion was that the vast majority of combat takes place at short ranges. In a highly mobile war combat teams ran into each other largely by surprise, and the team with the higher firepower tended to win every time. They also found that the chance of being hit in combat was essentially random -- that is, accurate "aiming" made little difference because the targets no longer sat still. The number one predictor of casualties was the total number of bullets fired.
These conclusions suggested that infantry should be equipped with a fully automatic rifle of some sort, in order to increase the rate of fire. However, it was also clear that such weapons dramatically increased ammunition use, in order for a rifleman to be able to carry enough ammunition for a firefight, they would have to carry something much lighter.
For both of these reasons, existing rifles were poorly suited to real-world combat. Although it appeared the new T44 (precursor to the [[M14 (rifle)|M14]]) would increase the rate of fire, its heavy ammunition made carrying enough of it a real problem. Moreover the length and weight of the gun meant it was not really suitable for short range combat, where a smaller and lighter weapon could be brought to bear much more quickly.
These efforts had not gone unnoticed by René Studler, U.S. Army Ordnance's Chief of Small Arms Research and Development. He was upset about the civilian agency that was treading on "his" turf, and started an effort to support the "full power" round developed for the T25, [[Springfield Armory]]'s competitor to the T44. In the end, he asked the [[Aberdeen Proving Ground]] to submit a report on the smaller caliber weapons.
This plan backfired when his assigned research lead, Donald Hall, found that a .22 in (5.59 mm) round would have equal performance to larger rounds in most combat situations. With the higher rate of fire possible due to lower recoil, it was likely such a weapon would inflict more casualties on the enemy. His team members, notably William C. Davis Jr. and G.A. Gustafson, started development of a series of experimental .224 in (5.69 mm) rounds. In 1955, their request for further funding was denied.
A new study, Project SALVO, was set up to try to find a weapon design suited to real-world combat. Running between 1953 and 1957 in two phases, SALVO eventually suggested that a weapon firing four rounds into a 20 in (0.5 m) area would have double the hit probability of existing semi-automatic weapons.
In the second phase, SALVO II, several experimental weapons concepts were tested. Irwin Barr of AAI introduced a series of [[flechette]] weapons, starting with a shotgun shell containing 32 darts and ending with single-round flechette "rifles". Winchester and Springfield offer multi-barrel weapons, while ORO's own design used two .22, .25 or .27 bullets loaded into a single .308 or .30-06 cartridge.
===Eugene Stoner===
Meanwhile testing of the T44 continued, and [[Fabrique Nationale]] via the American firm of Harrington & Richardson also submitted their new [[FN FAL]] into testing as the T48. However, the results of the testing were apparently already a forgone conclusion; the T44 was selected as the new battle rifle for the U.S. Army.
But this did not occur before a newcomer seriously upset the contest. In 1954, [[Eugene Stoner]] of the newly-formed [[ArmaLite]] started development of the [[AR-10]]. Springfield's T44 and similar entries were conventional in every meaning of the term, using wood for the "furniture" and otherwise built entirely of steel. ArmaLite was founded specifically to bring the latest in designs and alloys to firearms design, and Stoner felt he could easily beat the other offerings.
Stoner's design was radical, to say the least. The barrel was composite, consisting of a thin steel liner carrying the rifling, inside an aluminum alloy tube giving it strength. The receiver was made of milled aluminum instead of steel. The barrel liner extended into the receiver area where it met the bolt to provide a steel-on-steel lock for the mechanism. The bolt was operated by gases vented from the front of the barrel directly onto a cam on the bolt in the receiver, as opposed to the traditional method of using a long rod to push it. All of the furniture (the stock and grips) were made of plastic instead of wood, and even the flash hider was lightened by making it out of titanium.
Meanwhile the layout of the gun itself was also radically changed. Typical designs placed the sights directly on the barrel, using a bend in the stock to transfer the recoil to the shoulder. However this meant that the gun wanted to rise when fired, making it very difficult to control. Stoner's solution to this problem was to place the barrel in line with the stock, well below eye level, and then raise the sights up. The rear sight's carrier doubled as a convenient carrying handle.
The AR-10 was by far the most advanced design in the world at the time. At over two pounds (900 g) lighter than the competition and with much better recoil control, it should have easily won the contest. However, it was entered late and somewhat rushed, and the odd layout found few followers among the traditionalist big-round players. When a barrel burst in testing, the AR-10 was largely written off.
===CONARC===
In 1957, a copy of Gustafson's funding request from 1955 found its way into the hands of General Willard Wyman, commander of the U.S. Continental Army Command (CONARC). He immediately put together a team to develop a .22 caliber weapon for testing. Their finalized request called for a select-fire weapon of 6 pounds (2.7 kg) when loaded with 20 rounds of ammunition. The bullet had to penetrate a standard U.S. steel helmet, body armor, or a 0.135 inch (3.4 mm) steel plate at 500 yards (460 m), while equaling or exceeding the "wounding" ability of the .30 Carbine.
Having seen the AR-10 earlier, Wyman personally suggested that ArmaLite enter a weapon for testing. Stoner was working on a newer version of the AR-10 (the AR-16), but others at the company took up the challenge. Their first design, using conventional layout and wooden furniture, proved to be too light. When combined with a conventional stock, recoil was again a problem even with the light rounds. Their second design was simply a scaled-down AR-10, and immediately proved to be much more successful. Winchester entered a design based on their [[M1 Carbine]], and Earle Harvey of Springfield attempted to enter a design, but was overruled by his superiors at Springfield, who refused to divert resources from the T44.
In the end ArmaLite's [[AR-15]] really had no competition. The lighter round allowed it to be scaled down even smaller than the AR-10, and even after replacing the barrel with a simpler all-steel one, it was still well over a pound (450 g) lighter than the Winchester at 2.89 kilograms empty, about 3.5 kg loaded.
Its only major problem was that it wasn't fully developed before Army testing began nine months later on March 31st, 1958. Rainwater caused the barrels of both the ArmaLite and Winchester rifles to burst, causing the Army to once again press for a larger round, this time at .258 in. Nevertheless, they suggested continued testing for cold-weather suitability in Alaska. Stoner was later asked to fly in to replace several parts, and when he arrived he found the rifles had been improperly reassembled. When he returned he was surprised to learn that they too had rejected the design even before he had arrived, their report also "surprisingly" suggested the .258 round. After reading these reports, General [[Maxwell Taylor]] became dead-set against the design, and pressed for continued production of the M14.
Not all the reports were negative. In a series of mock-combat situations testing the AR-15, [[M-14|M14]] and [[AK-47]], Army testing found that the AR-15's small size and light weight allowed it to be brought to bear much more quickly, just as CONARC had suggested. Their final conclusion was that an 8 soldier team equipped with the AR-15 would have the same firepower as a current 11 soldier team armed with the M14. They also found that the AR-15 was more reliable than the M14, suffering fewer stoppages and jams in tests where thousands of rounds were fired.
At this point Fairchild had spent $1.45 million in development expenses, and there was no end in sight. Fairchild sold production rights for the AR-15 to [[Colt Firearms]] in December 1959, for only $75,000 cash and a 4.5% royalty on subsequent sales. In 1960 Armalite was reorganized, and Stoner left the company.
===M16 adoption===
A demonstration of the AR-15 was made to [[Curtis LeMay]] in June 1960. He immediately ordered 8,500 for defense at [[Strategic Air Command]] airbases. Colt Industries also approached the [[Advanced Research Projects Agency]] (ARPA), who bought 1000 rifles for use by South Vietnamese troops in the early summer of 1962. American [[special operations]] units working with the South Vietnamese troops filed remarkable battlefield reports, pressing for its immediate adoption.
U.S. [[Secretary of Defense]] [[Robert McNamara]] now had two conflicting views: the ARPA report favoring the AR-15 and the Pentagon's position on the M14. Even President [[John F. 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's test report stated only the M14 was suitable for Army use, but Vance wondered about the impartiality of those conducting the tests. He ordered the Army Inspector General to investigate the testing methods used, who reported that the testers showed undue favor to the M14.
McNamara ordered a halt to M14 production in January 1964. In November, the Army ordered 85,000 XM16E1s for experimental use, and the Air Force ordered another 19,000. Meanwhile the Army carried out another project, the Small Arms Weapons Systems (SAWS), on general infantry firearm needs in the immediate future. They highly recommended the immediate adoption of the weapon, so much so that they started referring to it as the M16. Later that year the Air Force officially accepted their first batch as the United States Rifle, Caliber 5.56 mm, M16. The Air Force M16s were different from the Army XM16E1s, which had a forward assist, as described below. The Air Force M16s were slightly modified AR-15s.
When the M14 reached [[Vietnam]] with U.S. troops in 1965 its flaws were instantly recognized. It was far too cumbersome and too heavy to use effectively in a close-quarters jungle environment, and the heavy ammunition meant only small quantities were carried on patrol. The fully automatic fire quickly demonstrated itself as useless, as the British had suggested, and the rifles were eventually delivered locked in semi-automatic. In the end the Army had spent a considerable amount of time and money switching from one semi-automatic weapon to another, and it appeared this happened largely due to internal politics. In defense of the M14 design, it was lighter and more reliable than the M1 Garand from which it evolved. While the M16 had the TCC and numerous changes to enhance its reliability, the M14 received no such attention. The Army chose to freeze the M14's design at an undeveloped stage.
Meanwhile the troops desperately tried to increase their own firepower in the face of the Viet Cong's Soviet-designed AK-47s. They took to scrounging any weapon they could find, the pre-WWII [[Tommy gun]] became particularly well-used. The XM16E1 was being introduced in increasing numbers, but quickly gained a bad reputation.
With the XM16E1 the Pentagon had demanded a change in the cartridge's propellant from the coarse-grained Improved Military Rifle (IMR) to the finer grained "ball" powder, which increased the automatic firing rate but also increased fouling of the bore and consequently caused the rifle to jam. To correct this, a "forward assist" plunger device to close the bolt in case of a misfeed was added. Colt, the Air Force, the Marine Corps and Eugene Stoner all agreed this device needlessly complicated the rifle and added about $4.50 to its procurement cost with no real benefit, but after another three years the Army ordered 840,000 of this version on February 28th, 1967. The version became known as the M16A1.
[[Image:M-16 gas impingement system.JPG|none|M16 direct gas impingement system]]
Colt had oversold the M16's reliability during testing, to the point where they claimed it never had to be cleaned. While this may have been true with the original IMR powder the rifle was developed with, it was not the case with the more finely-grained, faster-burning ball powder that was considerably "dirtier". The [[direct impingement]] gas operating system used a tube along the top of the barrel that vented gas back into a 'piston' formed behind the bolt and the recess in the bolt carrier. When combustion gases reached this area, they drove the bolt carrier to the rear and then vented the excess gas out the ejection port and out between the gas key at the top of the bolt carrier and the gas tube from the port in the barrel. Conventional designs keep the piston above or below the barrel and vent excess gas at that point. The advantage of the Stoner system was that the 'piston' formed by the bolt and bolt carrier operated in a direct line and on the same axis as the bore of the rifle. This resulted in no adverse movement of the bore axis due to the movement of the bolt carrier assembly. The adverse result of this design is that when the propellant gas is traveling down the tube, it cools and condenses becoming solid carbon. This carbon builds up in the action of the gun quickly. The M-16 therefore requires frequent cleaning to remain reliable.
Making matters worse, troops were told the weapon required no cleaning because of its [[space age]] construction, and had not been supplied with cleaning kits. In the field the guns started jamming all the time. Soldiers often derisively referred to them as "toy guns" and used the [[catch phrase]] "You can tell it's [[Mattel]]" when one malfunctioned. This later blossomed into an [[urban legend]] that the first M16s were actually manufactured by the [[toy]] giant.
The M16 debate once again took off, both in the Army and in [[Washington, DC]]. Stoner's latest design, a family of weapons known as the [[Stoner 63]], were sent to Vietnam for testing, while the [[SPIW]] flechette test weapon program was re-activated.
Luckily cooler heads prevailed. Cleaning kits were quickly produced, and a [[comic book]] was circulated among the troops to demonstrate proper maintenance. The reliability problems disappeared almost overnight, although the reputation did not. This did not appear to be true for the North Vietnamese troops, however, who started to use the rifle whenever one could be found.
Perhaps the most important change to the M16A1 was the introduction of chrome plating in the chamber, and some time later, the barrel as well. This improvement had been suggested in the original SALVO tests, but was dismissed as not cost-effective or practical. At the time, no reliable way had been devised to chrome-plate a .224" diameter barrel. The true value of Chrome Plating is preventing corrosion in the Chamber. Being a nearly straight-walled chamber, the slightest quantity of rust, corroded brass, sand, fouling, or even machining marks increase friction exponentially. Soldiers in the field found that the first round nearly always fired but would stick in the chamber. This is why the [[AK-47]] was designed with a tapered chamber. Chrome lining not only prevents rust, but it also decreases friction. Fouling that does get into the chamber is pressed into the side of the fired case and ejected along with it.
After its rocky start, the M16 has proven itself to be one of the more reliable combat rifles. By the end of 1967, the troops, when asked, would only trade in their M16s for the [[XM177]], a carbine version of the same weapon.
The lightweight round was likewise a matter of much debate in the rifle community. The "big round" concept refused to die for many years, and calls for an increase in caliber continued into the 1980s. Much of the debate centered on the Soviet Union's use of a larger StG44-style cartridge, the 7.62 x 39 mm, cut down from their wartime 7.62 x 54 mmR "full power" design. The debate ended for good when in the early 1970s the USSR introduced their own small round, one even smaller than the M16 at only 5.45 x 39 mm. Apparently SALVO had the right idea all along.
===NATO standardization===
In March 1970, the Pentagon shocked other NATO nations by stating all U.S. forces assigned to NATO would be equipped with the M16A1. The British military was highly vocal in voicing its anger after being thrashed by American Ordnance personnel into adopting the 7.62 mm NATO round because their .280 caliber round wasn't effective enough nearly twenty years earlier. Now they were being told the U.S. recognized the need for such a caliber of firearm after all, and was willing to start the NATO standardization of a lighter round after all.
But by the middle of the 1970s other armies were also looking at an M16 style weapon. A NATO standardization effort soon started, and tests of various rounds were carried out starting in 1977. The U.S. offered their original design, the M193, with no modifications, but there were serious concerns about its penetration in the face of the wider introduction of [[body armor]]. The British introduced a modified 5.56 mm round, using a longer and thinner bullet of 4.85 mm, mounted in the existing U.S. cartridges. The round had somewhat better ballistics, and considerably better penetration, able to reach 600 m and meet their requirements for a squad automatic weapon (small [[machine gun]]). The Germans introduced a new 4.7 mm caseless round, which was considerably lighter while offering similar ballistics to the original U.S. design. However, there was considerable distrust of the system due to the possibility of "cook off". A final design was offered by the Belgians, the SS-109, a new round also based on the U.S. cartridge and a new bullet with the same 5.56 mm caliber, but with a small tip of steel to improve penetration.
Testing soon showed that the British and Belgian designs were roughly equal, both outperforming the original U.S. design. In order to get full performance from the SS-109, however, the barrels would have to use a 1-in-7 twist in the rifling, and in the existing 1-in-9 it offered almost no advantage over the M193. In the end, it appears that the Belgian round was an easier sell to the U.S. Army, even though either round would require all-new rifles. The resulting M16A2, introduced in 1982, has been the standard U.S. military rifle since then.
After all of the debate, the M16 is still considered to be one of the best combat rifles ever produced. Total world-wide production is about 8 million.
==Future replacement?==
===Overview===
In the 1980s, many soldiers who had been equipped with M16A1s were given a [[M249]] (in addition to the M60s it replaced). In the 1990s, the adoption of the M4 Carbine meant many more M16A2s would be replaced by it. The Air Force currently plans to replace all its M16s with M4s according to a 2004 presentation. The M16A2 still remains the main US service rifle in the Army, though in the 2000s the Marine Corp moved to M16A4 rifles. Also the M16 never entirely replaced the M14 in all roles, which continues to be used in a number of niche applications throughout the Armed Forces.
The M16 family itself would have potentially been replaced at various points, and its longevity is in part due to a series of delays and failures in projects to replace it. It was going to be replaced by the winner of the Advanced Combat Rifle program, but none scored high enough to be worth the cost of changing over. It was also potentially going to be replaced by the SABR, from the OICW project. The rifle originally planned by the OICW project was put on hold around the turn of century, in favor of simpler new 5.56 mm rifle project, that offered less far-reaching improvements. The [[XM8 rifle]] which resulted, was also potentially going to replace the M16 family. However, this too ran into problems around 2004-5 and was put on hold in favor of a competition. The new competition itself was put on hold in 2005 to take into account input from other services.
===History===
Throughout the 1970s the Army experimented with various materials to replace the brass casings. Brass has a number of features that make it almost ideal for a cartridge, including low-friction against steel which made it easier to extract, and its ability to carry away a considerable amount of heat from the weapon and thereby keep it cooler. However brass is also heavy and expensive, replacing it would lower both the cost and weight of the ammunition.
Aluminum and steel were popular materials for complete rounds, and AAI successfully developed a plastic blank. However none of these materials ever entered production for one reason or another. Completely caseless ammunition was also studied on several occasions, notably the German 4.7 mm designs, but issues with reliability and "cook off" were never completely solved.
Later in the 1980s the Advanced Combat Rifle program was run to find a replacement for the M16. The Army was pressing for a 100% increase in the ability for infantry to hit their targets, in the same way that SALVO had aimed to increase effectiveness by 100% through increased rate of fire.
Colt entered a modified M16A2 known as the Colt ACR, which used duplex rounds, used a system that lowered recoil by 40% to allow better repeating shots, and added a 3.5x scope. The [[Steyr ACR]] used new flechette ammunition that was nominally called 5.56 mm, with a very high 4750 ft/s (1450 m/s) muzzle velocity. Other variants experimented with [[caseless ammunition]] technologies as well.
Although they all offered some improvement, none came close to the benchmark set for the testing.
More recently the Army has started the [[XM8]] system project for a radically improved weapon. However, the program has been shelved in favor of an open competition for what is now known as OICW Increment 1. (Increment 2 is the stand-alone airbursting grenade launcher known as the XM25, and Increment 3 will be the XM29, a weapon which combines the earlier two increments.)
==Design==
[[Image:Usafm16.jpg|thumb|right|200px|Top drawing is of an A2 style rifle; Bottom drawing is of an A2 style rifle with A1 rear sights (As with the Diemaco C7)]]
The M16 is made of [[aluminum]] alloy and [[plastics]], except for the steel barrel and parts of the action. Early models were especially lightweight at 3.2 kg (7.5 lb), about 30% less than older 7.62 mm "battle rifles" of the 1950s and 1960s. It also compares very favourably with the 5 kg (loaded) [[AK47]]. New models weigh more (8.5 lb or 3.9 kg) because of the "heavy" barrel used to increase accuracy. The rifle is 40 inches (1.02 m) long with standard 20 inch (508 mm) barrel. Stoner experimented with [[titanium]] barrels and receivers for even greater weight savings, but failed to achieve reliable operation at the time.
One distinctive ergonomic feature is a plastic or metal stock directly behind the action, which contains a [[recoil]] spring that serves the dual function of operating spring and recoil buffer. The straight-back stock and spring act to reduce muzzle rise, especially during automatic fire. As a result, most users find the M16 type rifle easy to use. Because recoil does not significantly shift the point of aim, user fatigue is reduced.
Another distinctive ergonomic feature is that the main sight is on the top of a carry handle on top of the receiver. This means that the user need not turn the head sideways to sight the rifle. The carry handle is also a popular feature. Newer models have a "flattop" upper receiver to which the user can attach either a conventional carry handle/sighting system or numerous optical devices such as [[night vision]] scopes.
The action is gas-operated, cocked by gases from a small hole in the barrel. The M16 design has a uniquely simple "direct drive" gas system, which also saves weight. Hot gases from the barrel vent directly into the receiver to push the bolt carrier rearward, eliminating the need for a traditional operating rod and spring assembly. While this reduces the number of moving parts and results in a simpler design, authorities differ about whether the design is more reliable than earlier service rifles.
The magazine release is on the right side of the rifle but releases are available for left-handed users. Current military magazines have 30 rounds, as opposed to the 20 round magazines issued in Vietnam. (30 round magazines were not developed and issued until late in the war.) Magazines are sometimes taped in upside-down pairs to speed reloading. Aftermarket double magazine clips are available. This practice is discouraged by military authorities because it is said to increase the chance that the top of a magazine will be damaged or pick up dirt. Nevertheless, all it takes is a quick look at recent pictures from Iraq (2004), to see that Special Forces and mainstream military forces are quick to make use of double magazine clips, as well as high-capacity magazines.
The bullet is small in caliber, 0.224 in (contrary to the 5.56 mm designation, the actual diameter is roughly 5.7 mm). The bullet often fragments when it strikes flesh. When fired from less than 100 meters, the bullet will penetrate 100 mm (4 in) into body tissue, before rotating 90 to 180 degrees. The force of bullet being pushed through dense tissue will then cause it to break nearly in half at the cannelure, which is a groove allowing the bullet casing to be sealed to the copper jacket. The rear section of the 5.56 mm bullet will then splinter into numerous tiny pieces, causing severe damage to surrounding tissue. The combination of high velocity and a fragile small bullet is more likely to cause incapacitating injuries than death by [[hydrostatic shock]]. The relatively small bullet drifts more than heavier bullets at long ranges, but users can be trained to compensate to a degree. For this reason the M16 and variants are well suited for urban and jungle warfare, unlike previous 7.62 mm infantry small arms, which cannot be fired successfully at close ranges as rapidly or with as much volume of fire.
The U.S. does not, generally, issue [[fully automatic]] M16-style rifles. Doctrinally, automatic fire is reserved for heavier machine guns that are designed to manage the recoil and deliver accurate fire even on fully automatic. Fully automatic fire would also expend ammunition faster, requiring soldiers to carry more to compensate. Also, the M16 barrel is too light to support sustained automatic fire and would overheat. Most M16- and M4-style weapons issued are capable of [[semiautomatic]] fire with an additional mode that utilizes a three-part automatic [[sear (firearm)|sear]] that fires three-round bursts for each pull of the [[trigger]], providing an "optimal" tradeoff of firepower, accuracy, and ammunition conservation. Colt did develop an AR variant made with a heavier barrel, belt-feed, and fast barrel replacement, but this was canceled in favor of the [[M249]] [[Squad Automatic Weapon]] in the 1970s. Squads are now issued the M249 (one per fireteam) to provide automatic fire. Fully automatic versions (the M16A3 and [[M4A1]]) are issued by the U.S. military to certain specialized units.
==Operation==
'''Safety Precaution''' (no magazine fitted) Safety precautions should be performed when taking possession of the weapon from another user, or any time the state of the weapon is unknown or in doubt. Always assume for safety purposes that such a weapon has a round in the chamber, ready to fire. Point the weapon in a safe direction, pull the cocking handle to the rear (a round may be ejected) and hold it there, examine the chamber to ensure it is clear, allow the action to go forward under control, push the forward assist, fire the action, and close the ejection port cover.
'''Safety Precaution''' (magazine fitted) Perform an "unload". If the above safety precaution is used with a charged magazine fitted a round will be chambered.
'''Load''' Insert a charged magazine into the magazine housing. There is a slight audible click when the magazine is properly fitted. The secureness of the magazine can be tested by gently trying to remove the magazine.
'''Ready''' Pull the charging handle all the way to the rear and release. Push the forward assist. If the weapon is not to be fired immediately then put the fire selector to "SAFE" and close the ejection port cover.
'''Fire''' [[Shooting|Marksmanship]] is a complex and subtle art and is beyond the scope of this article. However, in general the weapon is fired by putting the fire selector on either "SEMI" or "BURST" ("AUTO" on some models), resting the butt plate against the shoulder, aligning the eye of the firer, aperture of the rear sight, tip of the foresight, and target, and squeezing the trigger.
'''Unload''' Attempt to put the fire selector on "SAFE" (the selector will only go on "SAFE" if the hammer is depressed, i.e.: the weapon is cocked). Remove the magazine by pressing the magazine release with the trigger hand while grasping the magazine with the other hand. Tilt the weapon to the right and cock the weapon (a round may be ejected). Pull the charging handle to the rear again and hold it. Tilt the weapon to the left and ensure the chamber is empty. Allow the action to go forward, push the forward assist, put the fire selector to "SEMI" and squeeze the trigger. Close the ejection port cover and recover the ejected round.
==Variants==
The original military-version XM16E1 was different in appearance from the pre-production AR-15 adding the forward assist. The M16A1, replacing the XM16E1 featured an improved "bird-cage" flash hider (replacing the old three-pronged flash hider, which was easier for foreign material to get into, and caught on twigs and leaves and the like.) Soon after its adoption, barrels with chromed chambers and later fully chromed bores were introduced for the M16A1 to down on malfunctions due to fouling and corrosion.
*M16A2
Modifications to the M16A2 were more extensive. In addition to the new rifling, the barrel itself was made considerably stronger at the "open end" in order to resist bending in the field. A new adjustable dual-aperture rear sight corrects for both windage and elevation for better ranged shots, possible with the new SS-109 rounds. The flash hider was again modified, this time to be closed on the bottom so it would not kick up dirt or snow when being fired prone. The front grip was also modified from the original triangular shape to a round one, which better fit smaller hands. The new handguards were also symmetrical so that armories only had to stock one type rather than separate left and right handguards. The buttstock was also redesigned to be longer and stronger. In fact, the new buttstock is said to be 10 times stronger than the original due to advances in plastics and design. The heavier bullet has a reduced [[muzzle velocity]] from 3200 ft/s (975 m/s) in the earlier models, to about 2900 ft/s (884 m/s) in the A2. A special spent case deflector was incorporated into the upper receiver forging to the rear of the ejection port to prevent spent cases from striking left handed users.
The action was also modified to fire either semi-automatic, or in three round bursts, as it was found troops would often simply hold down the trigger and "spray" when under fire. The Army performed years of experiments to discover and verify that three-shot groups were optimum, originally in order to develop a flechette rifle.
In Vietnam, some soldiers were issued a [[carbine]] version of the M16 called the [[XM177]]. The XM177 had a shorter barrel (~260 mm) 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 USAF's XM177 and he U.S. Army's XM177E1 variants differed over the latter’s inclusion of a forward assist. The final XM177E2 had a 290 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, but incorrectly, referenced as the CAR-15. The variants were issued in limited numbers to special forces, helicopter crews, Air Force pilots, officers, radio operators, artillerymen, and troops other than front line riflemen.
The XM177E2 led to the M733, essentially the same gun with an M16A2 receiver and internal improvements and a flash hider/compensator to reduce perceived recoil. The M4 Carbine was developed from these designs in the early 1990s, with a 14.5 inch (368 mm) barrel and a "flat top" railed receiver. 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]], the 2000s [[War on Terrorism]], and in [[Iraq]].
*M16A3
Some confusion continues to exist, in spite of the evidence provided by U.S. government manuals and other documentation, concerning the M16A3 and M16A4. The M16A3 was adopted in small numbers around the time of the introduction of the M16A2, primarily by the U.S. Navy for use by the SEALs. The M16A3 is identical to the A2, but instead features a Safe-Semi-Auto (S-1-F) trigger group like that of the A1.
Descriptions of the M16A3 that claim that it is a flat top are incorrect. This misnomer most likely stems from the usage of the A2 and A3 designations by civilian manufacturers to differentiate between A2 style fixed carry handles and flat top receivers.
*M16A4
The M16A4, now standard issue for frontline U.S. Army and USMC units, replaces the fixed carry handle/rear iron sight with a M1913 Pictinny rail, allowing for the rifle to be equipped with a carry handle or most military and consumer scopes.
===Quick Reference===
{| border="1" cellpadding="4" cellspacing="0" style="margin: 1em 1em 1em 0; background: #f9f9f9; border: 1px #aaa solid; border-collapse: collapse; font-size: 95%;"
! Colt Model
! Army designation
! Air Force designation
! Barrel
! Handguard type
! Buttstock type
! Pistol grip type
! Lower receiver type
! Upper receiver type
! Rear sight type
! Muzzle device
! Forward assist?
! Case deflector?
! Bayonet lug?
! Trigger pack
|-
|601
|N/A
|AR-15
|20 in (508 mm) A1 profile
|Full-length triangular
|Fixed A1
|A1
|A1
|A1
|A1
|Type 1 Duckbill flash hider
|No
|No
|Yes
|S-1-F
|-
|603
|XM16E1
|N/A
|20 in (508 mm) A1 profile
|Full-length triangular
|Fixed A1
|A1
|A1
|A1
|A1
|Type 2 Duckbill flash hider
|Yes
|No
|Yes
|S-1-F
|-
|603
|M16A1
|N/A
|20 in (508 mm) A1 profile
|Full-length triangular
|Fixed A1
|A1
|A1
|A1
|A1
|M16A1-style flash hider
|Yes
|No
|Yes
|S-1-F
|-
|604
|XM16
|N/A
|20 in (508 mm) A1 profile
|Full-length triangular
|Fixed A1
|A1
|A1
|A1
|A1
|Type 2 Duckbill flash hider
|No
|No
|Yes
|S-1-F
|-
|604
|M16
|N/A
|20 in (508 mm) A1 profile
|Full-length triangular
|Fixed A1
|A1
|A1
|A1
|A1
|M16A1-style flash hider
|No
|No
|Yes
|S-1-F
|-
|N/A
|M16A1 PIP
|N/A
|20 in (508 mm) A1 profile
|Full-length ribbed
|Fixed A2
|A2
|A1
|A1
|A2
|M16A1-style flash hider
|Yes
|No
|Yes
|S-1-F
|-
|645
|M16A1E1/M16A2
|N/A
|20 in (508 mm) A2 profile
|Full-length ribbed
|Fixed A2
|A2
|A2
|A2
|A2
|M16A2-style flash hider
|Yes
|No
|Yes
|S-1-3
|-
|645E
|M16A2E1
|N/A
|20 in (508 mm) A2 profile
|Full-length ribbed
|Fixed A2
|A2
|A2
|Flat Top integral scope mount (pre-M1913 spec)
|N/A
|M16A2-style flash hider
|Yes
|No
|Yes
|S-1-3
|-
|Unknown
|M16A2E2
|N/A
|20 in (508 mm) A2 profile
|Full-length ribbed w/ HEL guide
|Fixed A2
|A2
|A2
|Flat Top integral scope mount (pre-M1913 spec)
|N/A
|M16A2-style flash hider
|Yes
|No
|Yes
|S-1-3
|-
|646
|M16A2E3/M16A3
|N/A
|20 in (508 mm) A2 profile
|Full-length ribbed
|Fixed A2
|A2
|A2
|A2
|A2
|M16A2-style flash hider
|Yes
|No
|Yes
|S-1-F
|-
|945
|M16A2E4/M16A4
|N/A
|20 in (508 mm) A2 profile
|Full-length ribbed or KAC M5 RAS
|Fixed A2
|A2
|A2
|Flat Top
|N/A
|M16A2-style flash hider
|Yes
|No
|Yes
|S-1-3
|}
==Production and usage==
The M16 is the most commonly manufactured 5.56 x 45 mm weapon in the world. Currently, the M16/M4 system is in use by 15 NATO countries and more than 80 countries world wide. Together, the [[United States|U.S.]], [[Canada]] (as the [[Diemaco C7|C7]]), [[Singapore]], and [[China]] have produced more than 8,000,000 units with approximately 90% still in operation [http://www.colt.com/mil/customers.asp].
In U.S service, the M16 primarily replaced the [[M14]] and [[M1 Carbine]] series as standard infantry rifles, and to a lesser extent, some of the jobs of the [[Browning_Automatic_Rifle|BAR]] Light automatic rifle. The M14 would go on to see service as a [[sniper Rifle]], and as a [[designated marksmen]] rifle.
==See also==
*[[AR-15]]
*[[M4 Carbine]]
*[[M203]] grenade launcher
*[[XM26 LSS]] shotgun
*[[XM29 OICW]]
*[[XM320]] grenade launcher
*[[List of individual weapons of the U.S. Armed Forces]]
*[[List of weapons of the U.S. Marine Corps]]
*[[Diemaco C7]]
*[[Diemaco C8]]
*[[SAR-21]]
*[[AK-47]]
*[[AK-74]]
==External links==
*[http://www.isayeret.com/weapons/assault/m4/m4.htm Israeli Special Forces Home Page: M16A2 Overview]
*[http://www.colt.com/mil/M16.asp Colt manufacturing: The M16A4 Rifle]
*[http://world.guns.ru/assault/as18-e.htm Modern Firearms]
*[http://www.thegunzone.com/556dw.html The Gun Zone: A 5.56 mm Timeline]
[[de:M16 (Gewehr)]]
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[[sl:M16]]
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[[zh:M16突击步枪]]
[[Category:Assault rifles]]
[[Category:Vietnam War equipment]]
[[Category:Modern firearms of the United States]]
[[Category:Cold War firearms of the United States]]
[[Category:Rifles of the United States]]
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