M16 rifle
 An M16A2 assault rifle |
|
| M16 | |
|---|---|
| Type | Service rifle |
| Nation(s) of Origin | United States of America |
| Era | Vietnam War, modern |
| History | |
| Date of design | 1957 |
| Production period | 1960— |
| Service duration | 1960–present |
| Operators | NATO |
| War service | Vietnam War, Gulf War, Iraq War |
| Variants | M4 Carbine |
| Number built | Over 8 million |
| Specifications | |
| Type | Selective fire rifle |
| Caliber | 5.56 mm |
| Barrel length | 508 mm (20 in) |
| Ammunition | 5.56 x 45 mm NATO, .223 Remington |
| Magazine | 20 or 30-round detachable box (see Design) |
| Action | Gas-operated, rotating bolt |
| Length | 1,002 mm (39.4 in) |
| Weight | See Design |
| Rate of fire | 750 to 900 round/min, cyclic |
| Muzzle velocity | 975 m/s (3,200 ft/s), 884 m/s (2,900 ft/s) (see Variants) |
| Effective range | 550 m (600 yd) |
| AR-15 related firearm articles. |
|
AR-10,
AR-15 |
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 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.
The M16 is a lightweight, 5.56 mm caliber, air-cooled, gas-operated, magazine-fed rifle, with a rotating bolt, actuated by direct impingement gas operation. It is constructed of steel, aluminum and composite plastics.
There have been three main iterations of the M16. The first was M16 and M16A1 models, fielded in the 1960s that fired a U.S. M193/M196 round that could fire either semi or fully-automatically. The second was the M16A2, which entered service in the 1980s and is intended to fire the Belgian M855/M856 rounds (5.56 mm NATO). The M16A2 can fire either semi-automatic or bursts of up to three rounds. Mode of fire is determined by using a selector switch on the side of the weapon. Finally, the M16A4 became standard issue for the United States Marine Corps during Operation Iraqi Freedom, increasingly replacing the earlier M16A2. In the U.S. Army, a combination of the M16A4 and M4 Carbine continue to replace existing M16A2s. The M16A4 features a handguard with four Picatinny rails for mounting optical sights, laser pointers, night vision, forward handgrips and flashlights.
Despite some early problems, the M16 has matured into a reasonably reliable weapon system. It is primarily manufactured by Colt and Fabrique Nationale, with variants produced by numerous countries around the world. The semi-automatic version, the AR-15, is a popular recreational firearm in the United States being made by a handful of larger manufacturers and over a dozen smaller concerns.
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. Various modified versions of the M16 design were subsequently fielded under experimental designations, culminating in the M16A1. The M16A1 was simply the M16 with a forward assist as requested by the Army. This weapon remained the primary infantry rifle of the United States military from 1967 until the 1980s, when it was supplemented by the M16A2. The M16A2, in turn, is currently being supplemented by the M16A4, which incorporates the modular flattop receiver unit developed for the M4 Carbine. Previous versions of the weapon are still in stock and used primarily by reserve and national guard units in the United States as well as by the U.S. Air Force. The M16A3 is a fully-automatic variant of the M16A2, issued primarily within the U.S. Navy.
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. 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) 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, which Springfield Armory developed prior 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 also submitted their new FN FAL via the American firm of Harrington & Richardson 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 despite a strong showing by the T48.
Acceptance of the M14 did not occur before a newcomer entered the contest. In 1954, Eugene Stoner of the newly-formed ArmaLite helped develop the AR-10. Springfield's T44 and similar entries were conventional rifles using wood for the "furniture" and otherwise built entirely of steel using mostly forged and machined parts. 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 for its day. The barrel was composite, consisting of a stainless steel liner carrying the rifling, inside an aluminum alloy tube for stiffness and heat dissipation. The receiver was made of forged and milled aluminum instead of steel. The barrel was mated to the receiver by a separate hardened steel adapter to which the bolt locked. This allowed a lightweight aluminum receiver to be used while still maintaining a steel-on-steel lockup. The bolt was operated by gases vented from the front of the barrel directly into a cylinder created in the bolt carrier with the bolt itself acting as a piston. Traditional rifles located this cylinder and piston close to the gas vent. The stock and grips were made of a plastic-reinforced fiberglass shell over a rigid foam plastic core. Even the flash suppressor was fabricated from titanium.
Meanwhile the layout of the gun itself was also somewhat different. Typical designs placed the sights directly on the barrel, using a bend in the stock to transfer the recoil to the shoulder to keep the sights at eye level. However this meant that the gun tended to rise when fired, making it very difficult to control especially under fully-automatic fire. The Armalite team used a solution borrowed from the German FG42 and Johnson Light Machinegun, placing the barrel in line with the stock, well below eye level, and then raise the sights up. The rear sight was built into a convenient carrying handle. The carrying handle also enclosed the charging handle which was on top of the receiver.
The AR-10 was a very advanced design for its time. At over two pounds (900 g) lighter than the competition, it also offered significantly greater recoil control. However, it was entered late and somewhat rushed, and the unconventional layout found few followers among the traditionalist big-round players. When a stainless, steel-lined aluminum barrel burst in 1957, the AR-10 was no longer considered viable. It did, however, provide enough of a showing to warrant further development for the new, small-caliber, high-velocity concept then being developed.
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 (5.6 mm) 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 entered 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, and 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 31, 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 (6.55 mm). 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 in (6.55 mm) 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, M14 and AK-47, the Army 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-man team equipped with the AR-15 would have the same firepower as a current 11-man 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 1,000 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, certain flaws became apparent for certain types of use. It was somewhat cumbersome to be highly effective in a close-quarters urban or jungle environment, although it was lighter than many dedicated CQB firearms. The ammunition was lighter than .30-06, which meant more quantities were carried on patrol, though it was heavier than the .30 Carbine. The fully-automatic fire is often criticized as useless, 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 firearm to another improved one, one that would have long — but small — service life. It would soon be replaced, even though this appeared to happen 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 less attention. The Army chose to field the M14's design after a lengthy development building on nearly 20 years experience on experiments with the Garand. While the M14 may have been a good replacement for the Garand, it was not very good at replacing the M1/M2/M3 Carbine.
Meanwhile the troops desperately tried to increase their own firepower in the face of the Vietcong's Soviet-designed AK-47s. They improvised with any weapon they could find, such as the pre-WWII Thompson submachine gun. The XM16E1 was being introduced in increasing numbers, but quickly gained a bad reputation.
With the XM16E1, the Pentagon ordered a change in the cartridge's propellant from the coarse-grained Improved Military Rifle (IMR) to the finer grained "ball" powder. This increased the cyclic rate of fire, increasing wear on parts and causing increased fouling. Several problems were blamed on this simple change. Stoppages were generally due to a corroded chamber, poor maintenance, worn parts, or a combination of these. Although dirtier, the ball powder only added to the increased wearing. The solution was to redesign the buffer to slow down the cyclic rate of fire, at which point parts breakage returned to normal. As a testament, ball powder is still used today in issue ammunition.
A "forward assist" plunger device was designed to close the bolt in case of a misfeed. 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 28, 1967. The version became known as the M16A1.
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. Therefore, the M16 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. As a result, the weapons frequently jammed in the field. 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 partially, or completely, 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 reactivated.
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 diminished quickly, 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-inch 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, rust pitting, 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 (7.1 mm) round wasn't effective enough nearly 20 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.
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 SS109, 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 SS109, however, the barrels would have to use a 1-in-7 twist in the rifling, and in the existing 1-in-12 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.
Total worldwide 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 U.S. service rifle in the Army, though in the 2000s the Marine Corps 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.
Replacement of the M16 family has been proposed at various points, and its longevity is in part due to a series of delays and failures in projects meant 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 weapon system originally planned by the OICW project was put on hold around the turn of century, in favor of a simpler new 5.56 mm rifle project that offered less far-reaching improvements. The resulting XM8 rifle was also intended as a potential replacement for the M16 family. However, this program too ran into problems around 2004-5, and was put on hold in favor of a competition for what became known as the OICW Increment 1. The OICW-1 competition was put on hold in the summer of 2005 to take into account input from other services, and several months later was cancelled outright.
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. This weapon, designated M16A2E2, also featured a "guide" of sorts as part of a special handguard developed by the U.S. Army Human Engineering Laboratory (HEL) designed to assist in snap-shooting, and a carbine style stock very similar to the recent stock developed by the Naval Surface Warfare Center, Crane Division.
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 started the XM8 system project for a radically improved weapon. However, the program was shelved in favor of an open competition for what became 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.) The OICW-1 competition was cancelled on October 31, 2005.
Design
The M16's receivers are made of aluminum alloy, its barrel, bolt, and bolt carrier of steel, and its forestock, pistol grip, and buttstock of plastics. Early models were especially lightweight at 2.9 kg (6.4 lb). This was significantly less than older 7.62 mm "battle rifles" of the 1950s and 1960s. It also compares very favorably with the 5 kg (loaded) AK47. New models weigh more (8.5 lb or 3.9 kg) because of the "heavy" barrel profile in front of the front site. This was to prevent bending. The profile under the handguards remained the same for compatibility with clamp-on grenade launchers. The rifle is 40 inches (1.02 m) long with standard 20-inch (508 mm) barrel. Stoner experimented with titanium barrels in the prototype AR-10 for weight savings, but one barrel burst in the test. Stoner contended that the test had been rigged.
One distinctive ergonomic feature is a plastic or metal stock directly behind the action, which contains a recoil spring. This serves the dual function of operating spring and recoil buffer. The stock being in line with the bore reduces muzzle rise, especially during automatic fire. 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. Newer models have a "flattop" upper receiver with a picatinny mounting rail to which the user can attach either a conventional carry handle/sighting system or numerous optical devices such as night vision scopes.
The M16 utilizes direct impingement gas operation; energy from high-pressure gas tapped from a port halfway down the barrel actuates the moving parts in the weapon. Combustion gases travel directly into a chamber in the bolt carrier behind the bolt itself, pushing the carrier away from the bolt. This reduces the number of moving parts by eliminating the need for a separate piston and cylinder.
The primary fault of direct impingement is that fouling and debris from expended gunpowder is blown directly into the breach. As the superheated combustion gas travels down the tube, it expands and cools, not unlike an aerosol can cools when depressurized. This cooling causes vaporized matter to condense as it cools depositing a much greater volume of solids and doing so right on the operating parts in the action. Conversely, gas-piston operation uses high-pressure gasses for very short periods of time and keeps those gasses away from the breech. Because of this, the M16 requires more frequent cleaning and lubrication for reliable operation compared to gas piston operation.
The magazine release is on the right side of the rifle ahead of the trigger guard. Current military magazines have a capacity of 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.) 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, recent pictures from Iraq (2004) show that Special Forces and mainstream military forces are quick to make use of double magazine clips.
The M193 bullet routinely fragments when it strikes soft tissue. When fired from less than 100 meters, the bullet will penetrate 100 mm (4 in) into body tissue, before yawing 90 to 180 degrees. Fragmentation occurs latteral forces on the bullet cause it to break in half. This occurs at the weak 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 fragment into numerous tiny pieces, causing increased damage to surrounding tissue.
The U.S. does not, generally, issue fully-automatic M16-style rifles. Most M4 variants trade 3-round burst for automatic fire that is more effective in close-quarters weapon. 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 semi-automatic fire. The burst-fire mechanism utilizes a three-part automatic sear that fires up to a three-round burst for each pull of the trigger. It is non resetting meaning that if a soldier fires a two-round burst and releases the trigger, he will encounter a single-round fired the next burst. Burst mechanisms provide a tradeoff between firepower, accuracy, and ammunition conservation. They do, however, limit the effectiveness of the M16 when used in suppression, ambush situations, and close-quarters combat.
Colt developed a variant with a heavier barrel, belt-feed, and fast barrel replacement. This was intended to provide a squad with the firepower of a machinegun with the portability of the M16. This was canceled in favor of the M249 Squad Automatic Weapon in the 1970s. Squads are now issued the M249 (one per fire team) 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. Strike it from the base with medium firmness to make sure it locks home.
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
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.
Production and usage
The M16 is the most commonly manufactured 5.56 x 45 mm rifle in the world. Currently, the M16/M4 system is in use by 15 NATO countries and more than 80 countries world wide. Together, the U.S., Canada (as the C7), Singapore, and China have produced more than 8,000,000 units with approximately 90% still in operation [1].
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 BAR Light automatic rifle. The M14 would go on to see service as a sniper rifle, and as a designated marksmen rifle.
Users of the M16 rifle and its variants have included and are: Australia, Barbados, Belize, Bolivia, Botswana, Brazil, Brunei, Burma, Cambodia, Cameroon, Canada, Chile, Congo, Costa Rica, Denmark, Dominican Republic, Fiji, France, Germany, Ghana, Greece, Grenada, Haiti, Honduras, Ireland, Israel, Kuwait, Liberia, Malaysia, Mexico, Morocco, New Zealand, Norway, Indonesia, Jamaica, Laos, Nigeria, Netherlands, Oman, Panama, Philippines, Qatar, Saudi Arabia, South Korea, Sri Lanka, Taiwan, Thailand, Tunisia, Turkey, United Kingdom, United States, Uruguay, and Vietnam. [2].
Variants
Colt Model's 601 and 602
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). The 601 and 602 are easily identified by their "slab-sideed" lower receivers without the commonly found "fencing" around the magazine well, and in certain cases their green or brown furniture. The 601 was adopted first of any of the rifles by the USAF, and was quickly supplemented with the XM16/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.
M16
Variant originally adopted by the USAF. This was the first M16 adopted operationally. This variant had triangular handguards, a three-pronged flash suppressor, and no forward assist. Bolt carriers were originally chrome plated and slick-sided, lacking any notches for a forward assist. Later, the chrome plated carriers were dropped in favor of Army issued notched and parkerized carriers. The Air Force continues to operate these weapons and upgrades them as parts wear or break and through attrition.
XM16E1 and M16A1
The prototype army-version, XM16E1, was essentially the same weapon as the M16 with the addition of a forward assist. The M16A1 was the finalized production model. To address issues raised by the XM16E1's testing cycle, a "bird-cage" flash suppressor replaced the XM16E1's three-pronged flash suppressor, which was too easy for foreign material to get into and which caught on twigs and leaves. After numerous problems in the field, numerous changes were fielded. Cleaning kits were developed and issued; barrels with chromed chambers and later fully-chromed bores were introduced. The number of malfunctions due to fouling and corrosion declined and later troops were generally unfamiliar with early problems.
M16A2
Modifications to the M16A2 were more 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. 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 SS-109 rounds. 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. The front grip was modified from the original triangular shape to a round one, which better fit smaller hands. The new handguards were also symmetrical so that armories didn't need separate left and right spares. The buttstock was redesigned to be longer and stronger. The new buttstock is said to be ten times stronger than the original due to advances in plastics and design. The heavier bullet has a reduced muzzle velocity from 3,200 feet per second (975 m/s) in the earlier models, to about 2,900 feet per second (875 m/s) in the A2. A special spent case deflector was incorporated into the upper receiver to the rear of the ejection port to prevent spent casings from striking left-handed users.
The action was also modified, replacing the fully-automatic setting with a three-round burst setting. When using a fully-automatic weapon, poorly trained 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. There are mechanical flaws in the M16A2 burst mechanism. The trigger group does not reset when the trigger is released. If a soldier lets go of the trigger between the second and third round of the burst, for example, the next trigger pull would only result in a single shot. Even in semi-automatic mode, the trigger group mechanism affects weapon handling. With each round fired, the trigger group cycles through one of the three stages of the burst mechanism. The trigger pull at each of these stages is slightly different, detracting from accuracy, though not by any noticable amount for most shooters.
All together, the M16A2s new features added weight and complexity to the M16 while simultaneously decreasing barrel life and removing the fully-automatic setting. While the new gun was said to be more accurate, the heavier bullets had a more curved trajectory requiring more precise range estimation for accurate shot placement. Critics also point out that neither of the rear sight apertures is ideally sized. The small aperture is too small, making quick acquisition of the front site post difficult, and the large aperture is too large, resulting in decreased accuracy. To make matters worse, the rear sight apertures are not machined to be on the same plane. In other words, the point of impact changes when the user changes from one aperture to the other. The rear sight's range adjustment feature is rarely used in combat as soldiers tend to leave the rear sight on its lowest range setting: 300 meters. Despite criticism, a new rifle was needed both to comply with NATO standardization of the SS-109 (M855) and to replace aging Vietnam era weapons in the inventory.
M16A3
The M16A3 was a fully-automatic 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 the SEALs. It features a Safe-Semi-Auto (S-1-F) trigger group like that of the M16A1.
Some confusion continues to exist regarding the M16A3. It is often described as the fully-automatic version of the M16A4. Descriptions of the M16A3 that claim that it shares the M16A4's Picatinny rail are incorrect. This misunderstanding most likely stems from the usage of the A2 and A3 designations by civilian manufacturers to differentiate between A2-style fixed carry handles and Picatinny rail versions.
M16A4
The M16A4, now standard issue for frontline U.S. Army and USMC units, replaces the combination fixed carry handle/rear iron sight with a MIL-STD-1913 Picatinny rail, allowing for the rifle to be equipped with a carry handle and/or most military and consumer scopes or sighting systems. All of the U.S. Marine Corps' M16A4s are equipped with a Knight's Armament Company M5 RAS handguard, allowing vertical grips, lasers, tactical lights, and other accessories to be attached. U.S. Army M16A4s also often feature the KAC M5 RAS. In U.S. Army Field Manuals, M16A4s fitted with the RAS are sometimes referred to as M16A4 MWS or Modular Weapon System.
Specialist variants
Colt Model 655 and 656 "Sniper" variants
With the expanding conflict in South East Asia, 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 mount 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 3-9x 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, M4 carbine, and Colt Model 733
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 GAU-5/A (XM177) and the U.S. Army's XM177E1 variants differed over the latter’s inclusion of a forward assist. The final USAF GAU-5A/A and U.S. Army 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 referenced and marketed 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 M4 Carbine was developed from various outgrowths of these designs, including a number of 14.5" barreled A1 style carbines. The XM4 (Colt Model 720) started its trials in the mid-80s, with a 14.5 inch (368 mm) barrel. 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.
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. A more complete history of this weapon can be found with other information on the Colt Commando.
A Firing Port Weapon or FPW was also developed to work with the Bradley IFV, designated the M231.
Mk 4 Mod 0
The Mk 4 Mod 0 was a variant of the M16A1 produced for the U.S. Navy SEALs during the conflict in Vietnam 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 quarter-inch hole 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) 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 last 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 M16A1 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.
Summary
| Colt model no. | Military designation | Barrel Length | Barrel | Handguard type | Buttstock type | Pistol grip type | Lower receiver type | Upper receiver type | Rear sight type | Front sight type | Muzzle device | Forward assist? | Case deflector? | Bayonet lug? | Trigger pack |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 601 | AR-15 | 20 in (508 mm) | A1 profile (1/14 inch twist) | Green or brown full-length triangular | Green or brown fixed A1 | A1 | A1 | A1 | A1 | A1 | Duckbill flash suppressor | No | No | Yes | Safe-Semi-Auto |
| 602 | AR-15 or XM16 | 20 in (508 mm) | A1 profile (1/12 inch twist) | Full-length triangular | Fixed A1 | A1 | A1 | A1 | A1 | A1 | Duckbill or three-prong flash suppressor | No | No | Yes | Safe-Semi-Auto |
| 603 | XM16E1 | 20 in (508 mm) | A1 profile (1/12 twist) | Full-length triangular | Fixed A1 | A1 | A1 | A1 | A1 | A1 | Three-prong or M16A1 birdcage flash suppressor | Yes | No | Yes | Safe-Semi-Auto |
| 603 | M16A1 | 20 in (508 mm) | A1 profile (1/12 twist) | Full-length triangular | Fixed A1 | A1 | A1 | A1 | A1 | A1 | M16A1-style birdcage flash suppressor | Yes | No | Yes | Safe-Semi-Auto |
| 604 | M16 | 20 in (508 mm) | A1 profile (1/12 twist) | Full-length triangular | Fixed A1 | A1 | A1 | A1 | A1 | A1 | Three-prong or M16A1-style birdcage flash suppressor | No | No | Yes | Safe-Semi-Auto |
| 645 | M16A1E1/PIP | 20 in (508 mm) | A2 profile (1/7 twist) | Full-length ribbed | Fixed A2 | A1 | A1 or A2 | A1 or A2 | A1 or A2 | A2 | M16A1 or M16A2-style birdcage flash suppressor | Yes | Yes or No | Yes | Safe-Semi-Auto or Safe-Semi-Burst |
| 645 | M16A2 | 20 in (508 mm) | A2 profile (1/7 twist) | Full-length ribbed | Fixed A2 | A2 | A2 | A2 | A2 | A2 | M16A2-style birdcage flash suppressor | Yes | Yes | Yes | Safe-Semi-Burst |
| 645E | M16A2E1 | 20 in (508 mm) | A2 profile (1/7 twist) | Full-length ribbed | Fixed A2 | A2 | A2 | Flattop with Colt Rail | Flip-up | Folding | M16A2-style birdcage flash suppressor | Yes | Yes | Yes | Safe-Semi-Burst |
| N/A | M16A2E2 | 20 in (508 mm) | A2 profile (1/7 twist) | Full-length semi-beavertail w/ HEL guide | Retractable ACR | ACR | A2 | Flattop with Colt rail | None | A2 | ACR muzzle brake | Yes | Yes | Yes | Safe-Semi-Burst |
| 646 | M16A2E3/M16A3 | 20 in (508 mm) | A2 profile (1/7 twist) | Full-length ribbed | Fixed A2 | A2 | A2 | A2 | A2 | A2 | M16A2-style birdcage flash suppressor | Yes | Yes | Yes | Safe-Semi-Auto |
| 655 | M16A1 Special High Profile | 20 in (508 mm) | HBAR profile (1/12 twist) | Full-length triangular | Fixed A1 | A1 | A1 | A1 | A1 | A1 | M16A1-style birdcage flash suppressor | Yes | No | Yes | Safe-Semi-Auto |
| 656 | M16A1 Special Low Profile | 20 in (508 mm) | HBAR profile (1/12 twist) | Full-length triangular | Fixed A1 | A1 | A1 | A1 with modified Weaver base | Low Profile A1 | Hooded A1 | M16A1-style birdcage flash suppressor | Yes | No | Yes | Safe-Semi-Auto |
| 945 | M16A2E4/M16A4 | 20 in (508 mm) | A2 profile (1/7 twist) | Full-length ribbed or KAC M5 RAS | Fixed A2 | A2 | A2 | Flattop with MIL-STD-1913 rail | None | A4 | M16A2-style birdcage flash suppressor | Yes | Yes | Yes | Safe-Semi-Burst |
Popular culture
The M16 and its variants are almost ubiquitous in American and many other countries' films, TV series and video games. See M16 rifle in popular culture for a list of films and video games featuring the weapon.