First model ArmaLite Ar-15 rifle, with original 25-round magazine. Note the position of charging handle
Early model M16 rifle, as used by US AF, with early military issue 20-round magazine. Note the three-prong flash hider and the lack of forward assist
M16A1 rifle with 30-round magazine and bayonet, right side
M16A1 rifle with 20-round magazine, left side
M16A1 rifle with M203 40mm grenade launcher
M16A2 rifle with 30-round magazine, right side
M16A4 rifle with 30-round magazine and carrying handle installed over the Picatinny rail, right side
M16A4 rifle with RIS (Rai Interface System) installed around the barrel, and the Aimpoint red-dot signt installed on the rail instead of the detachable carrying handle
See the M16A1 field-stripping
See typical markings and controls on the M16A1 rifle
See M16A3 receiver X-ray image. Aluminum parts are in blue color, steel parts are black
Exploded view of the AR15
| M16A1 | M16A2 | M16A4 | |
| Caliber | 5.56x45mm (.223 Remington), M193 | 5.56x45mm NATO / M855 | 5.56x45mm NATO / M855 |
| Action | gas operated, rotating bolt | ||
| Overall length | 986 mm | 1006 mm | 1000 mm |
| Barrel length | 508 mm | 508 mm | 508 mm |
| Weight, empty | 2.89 kg | 3.77 kg | 3. 4 kg |
| Magazine capacity | 20 or 30 rounds standard | ||
| Rate of fire, cyclic | 650 - 750 rounds per minute | 700 - 950 rounds per minute | |
The story of the M16 rifle is one of most turbulent and controversial episodes in the whole history of US small arms. It was hastily adopted as an iterim measure, but eventually soldiered on to see more than 40 years of active service. Its early days were full of controversy and scandals, its present is full of competition, but it appears that this weapon will serve with American armed forces and abroad for at least several years (if not decades) more. Today it can be considered as adequate military rifle with good current service record. Obviously, it is far from being ideal, but no rifle in the world is ideal as well. We only have to see, if the American armed forces will eventually step up and produce a better rifle and / or cartridge in a foreseeable future.
The origins of the M16 rifle lay in the research, conducted soon after the Korean war by Operations Research Office (ORO), founded at Hopking University and sponsored by US Army. Among the reports, produced by the ORO, two are most significant in this respect, the so called Hall and Hitchmann reports. One report stressed the fact that most hits, achieved by soldiers in battle, were made at relatively short ranges (within 300 meters) and, mostly, at random. This significantly undermined the obsession for long-range aimed fire, promoted by the Army. Second report suggested, that the most effective way to increase the probability of hits in the battle is to fire multiple small caliber, high velocity projectiles with controlled dispersion instead of one, relatively heavy and large projectile as used in conventional rifles at the time. The latter concept initiated so called "Project SALVO", which was conducted between 1952 and 1957 to develop a proper concept of a new, small bore military rifle. There were several basic concepts, including different projectile types (standard bullets or small, arrow-like finned projectiles known as "flechettes"), fired by score from single round (to achieve 'shotgun' effect) or in rapid bursts of several rounds, each firing single projectile. Eventually, army selected the concept of weapon, firing controlled bursts of single flechettes (steel arrows with body diameter of amout 1.5mm) to go ahead, and called this APHHW - All Purpose Hand Held Weapon, later renamed to SPIW - Special Purpose Individual Weapon. In teh mean time, some elements within Army also sponsored a more conventional approach to the same problem, and oredered development of conventional automatic rifles, firing ordinary small-caliber bullets. During late 1950s and early 1960s there was a lot of experimentation and development in regard of new ammunition, optimal calibers and rifle designs. The problem was, that widely promoted SPIW program seemed to have no end, and the recently adopted "full-power" 7.62mm M14 rifle faced serious production problems.
Enter the Armalite. In the year of 1957 The US Army requests the Armalite Division of the Fairchild Aircraft Corp to develop a rifle of .22 caliber, lightweight, select-fire, and capable to penetrate the standard steel helmet at 500 meters. The Eugene Stoner, then a designer at the Armalite, began to develop this rifle, based on his earlier design, 7.62mm AR-10 battle rifle. At the same time, experts at the Sierra Bullets and the Remington, in conjunction with Armalite, began do develop a new .22 caliber cartridge, based on the .222 Remington and .222 Remington Magnum hunting cartridges. This development, initially called the .222 Remington Special, was finally released as .223 Remington (metric designation 5.56x45mm). Next year Army tests new rifles, known as Ar-15, and rejects these in favor of the M14. Feeling that the Ar-15 rifle has poor chances to compete with the recently adopted M14 in the US Military, in 1959 the Fairchild Corp, a parent company of the Armalite, sells all rights and manufacturing documentation for this rifle to the Colt's Patent Firearms Manufacturing Company, which had long-time relations with US Military and proven track of selling military guns both in USA and abroad. Colt instantly begins aggresive marketing campaign for the new rifle, stressing its accuracy, low recoil, light weight and modern design. In the 1962, US DoD Advanced Research Projects Agency (ARPA) purchases 1000 AR-15 rifles from Colt and sends those rifles to the South Vietnam, for field trials. Same year brings glowing reports about the effectiveness of the new "black rifle", used by South Vietnamese forces.
Following the delays in introduction of the ill-fated 'next generation' SPIW system and production troubles with M14, in 1963 Colt receives contracts from US Government for 85 000 rifles for US Army (designated as XM16E1) and for further 19 000 rifles for US Air Forces (designated M16). The US AF M16 was no more than an AR-15 rifle with appropriate markings. The XM16E1 differed from AR-15/M16 by having an additional device, the so called "forward assist", which was used to manually push the bolt group in place in the case of jams. Next year US Air Forces officially adopted new rifle as M16. Same year US Army adopted the XM16E1 as a limited standard rifle, to fill the niche between discontinued 7.62mm M14 rifle and the forthcoming SPIW system (which newer got past the prototype and trial stages).
With rapidly growing presence of US troops in Vietnam, in 1966 US Government makes the first large purchase of the Ar-15 / M16 rifles, ordering 840 000 rifles for US Armed forces, worth almost $92 millions, and in 1967 US Army officially adopts the XM16E1 rifle as a standard "US Rifle, 5.56mm, M16A1".
During immediately following years, a number of negative reports apears from Vietnam. M16A1 rifles, issued to US troops in the Vietnam, severely jammed in combat, resulting in numerous casualties. There were some causes for malfunction. First of all, during the introduction of the new rifle and its ammunition into the service, US Army replaced originally specified Dupont IMR powder with standard ball powder, used in 7.62x51mm NATO ammunition. The ball powder produced much more fouling, that quickly jammed the actions of the M16 unless the gun was cleared well and often. It also had different pressure curve, resulting in increased stress on operating parts of the gun. This pitifully combined with the fact that the initial M16 rifles were promoted by the Colt as "low maintenance", so, for the sake of economy, no cleaning supplies were procured for new M16 rifles, and no weapon care training was conducted fro the troops. As a result, soldiers did not knew how to clean their rifles, and had no provisions for cleaning, and things soon turned bad. Another cost-saving measure on the part of the Army was to give up with cromium plation of the barrel bore and bolt group, which made these parts much more sensitive to corrosion and rust that originally designed.
After several dramatic reports in US press and Congressional investigation of the troubles, several actions were taken to remedy the problems. The 5.56mm ammunition was now loaded using different powders that produce much less residue in the gun action. The barrel, chamber and bolt of the rifles were chrome-lined to improve corrosion resistance. Cleaning kits were procured and issued to troops, and a special training programs were developed and conducted ever since. Earliest cleaning kits could be carried separate from rifle only, but since circa 1970 all M16A1 rifles were manufactured with the containment cavity in the buttstock, that held the cleaning kit. At the same time (circa 1970) the new 30 rounds magazines were introduced into service instead of the original 20 rounds ones, to equal Soviet and Chinese AK-47 assault rifles, which had 30-rounds magazines from the very beginning.
Therefore, by the end of the US involvment in Vietnam war, the M16A1 rifle eventually became more or less mature. It gradually replaced older rifles in US service, and also influenced the work on the small-caliber ammunition and automatic firearms in other countries, including the USSR. This work culminated in the NATO trials, held in 1977 - 79, with intent to adopt a small-caliber, high-velocity cartridge to replace the potent, but somehow overly powerful 7.62mm NATO round as standard infantry rifle ammunition for the whole NATO organisation. Not surprisingly, the winner of the trials was the american 5.56x45mm cartridge, although in a version loaded with Belgian SS109 bullet, which provided better long-range ballistics than the original US 5.56mm M193 ammo.
In 1981, Colt developed a variation of the M16A1, adapted for the SS109/5.56mm NATO cartridge, and submitted it to the military trials as the M16A1E1. This rifle differed from the M16A1 by having the heavier barrel with faster 1:7 rifling, a different type rear sights (adjustable for both range and windage), round handguards instead of triangular ones, and by replacing the full-auto fire mode with the burst (limited to 3 rounds per trigger pull), to preserve the ammunition. It was officially adopted by US DoD as the "US Rifle, 5.56mm, M16A2" in 1982, which still is the primary infantry rifle for US Armed forces and a number of other armies and law enforcement organizations.
The development of the M16 rifle continued. By the mid-1990s, Colt, at the request of the US Special Forces, produced a carbine version of the M16A2, designated M4. This carbine traces its roots back to the 1960s vintage Colt CAR-15 carbine, but has several improvements. Actually, it was the M16A2 rifle, fitted with a shorter barrel and handguards, with the gas port moved back. The fixed buttstock was replaced by a retractable telescoping buttstock, originally designed in the mid-1960s by a Colt employee, Robert E. Roy for the Colt “Commando” carbines. The M4 was supposed to become the standard US Special Forces rifle, and could be fitted with the standard M16A2-type bayonet and the M203 40mm grenade launcher.
By 1996, the two newest versions of the M16 appeared, the M16A3 and M16A4. These differ from the M16A2 by having a removable carrying handle, with the upper receiver being fitted with a Picatinny-type accessory rail. Otherwise the M16A4 is similar to the M16A2, while the M16A3 also replaced the infamous three-round burst mode with a full auto mode. The key advantage of both the M16A3 and A4 rifles is the ability to quickly mount and re-mount a wide variety of optical, red dot or night vision / IR sights with MIL-STD 1913 (Picatinny-type) compatible mounts. The M4 carbine was also upgraded to “flat top” configuration, which is now standard.
The M16 is still a general-issue rifle with the US Armed forces. It is also widely used by the US Law Enforcement agencies, either in military form (for example, the LAPD had some M16s, retired from the Army), or in "civilian" semi-automatic only form. The AR-15 style rifles are made in the USA by at least a dozen large companies, such as ArmaLite, Bushmaster, Colt, FN Manufacturing, Hesse, Les Baer, Olympic, Wilson Combat, and by a number of smaller companies, many of which assemble their rifles from components made by other major manufacturers. M16-type rifles are also manufactured outside the USA, most notably in Canada, by Diemaco Co (now Colt Canada). China also makes some AR-15 type rifles at the NORINCO state factories, known as CQ. M16 rifles are used by many foreign military groups, most notably the British SAS, who preferred the M16 over the infamous L85A1 rifle, and by many others.
At the present time almost all of the initial flaws of the M16 have been removed and it is considered among the best assault rifles in the world. While its reliability in harsh conditions cannot match that of its main rival, the Kalashnikov AK-47 and AK-74, it is still a quite reliable weapon, especially when well maintained. It is also comfortable to fire and quite accurate.
It must be noted that during recent operations in Afghanistan and Iraq (2002 and 2003, respectively), there were several controversial complaints about the effectiveness and reliability of the M16A2 and M4 rifles. It seems that most complaints about the reliability of the M16A2 rifles came from inadequate troop training and the resulting improper handling of the rifles. The M4 carbines are a somewhat different story, since the problems can be partially traced to the shortened gas system, which now operates at higher pressures, thus more violently. The M4 also rapidly overheated. Another general complaint was about the poor effectiveness of the standard M855 ammunition, which lacked stopping power especially from shorter M4 carbine barrels. To partially cure this problem, the US SOCOM recently issued a new type of 5.56 mm ammunition, the Mk.262 mod.0, which is loaded with heavier Sierra Match King bullets, weighing 4.99 gram compared with the 4.0 gram bullet in the M855 cartridge. The most recent experience also clearly showed the excessive length of the M16A2 rifles, which are too clumsy for motorised troops, riding in cars, armored carriers and helicopters. At the present time, many M16A2 rifles are being replaced in the hands of US troops with more compact and maneuverable M4A1 carbines.
One of the key advantages of the Stoner design, that must be especially stressed, is the extreme flexibility of the construction. At the present time the interchangeable complete upper receiver assemblies ("upper" in short) are available in various barrel lengths and profiles (from 7 to 24 inches long, slim and heavy), in dozens of rifle and pistol calibers (from tiny but fast .17 Remington and up to monstrous .458 SOCOM, and from .22LR and 9mm Luger up to mighty .50AE). Special, manually single-shot uppers are commercially available in the extremely powerful .50BMG (12.7x99mm) caliber. Various "lower receiver" assemblies offer a broad variety of trigger units, buttstocks and other options. This advantage is viable for both military (especially Spec Ops), Law Enforcement, and civilian applications, as it allows to tailor any particular AR-15 type rifle to the current situation and tactical needs.
The origins of the M16 rifle lay in the research, conducted soon after the Korean war by Operations Research Office (ORO), founded at Hopking University and sponsored by US Army. Among the reports, produced by the ORO, two are most significant in this respect, the so called Hall and Hitchmann reports. One report stressed the fact that most hits, achieved by soldiers in battle, were made at relatively short ranges (within 300 meters) and, mostly, at random. This significantly undermined the obsession for long-range aimed fire, promoted by the Army. Second report suggested, that the most effective way to increase the probability of hits in the battle is to fire multiple small caliber, high velocity projectiles with controlled dispersion instead of one, relatively heavy and large projectile as used in conventional rifles at the time. The latter concept initiated so called "Project SALVO", which was conducted between 1952 and 1957 to develop a proper concept of a new, small bore military rifle. There were several basic concepts, including different projectile types (standard bullets or small, arrow-like finned projectiles known as "flechettes"), fired by score from single round (to achieve 'shotgun' effect) or in rapid bursts of several rounds, each firing single projectile. Eventually, army selected the concept of weapon, firing controlled bursts of single flechettes (steel arrows with body diameter of amout 1.5mm) to go ahead, and called this APHHW - All Purpose Hand Held Weapon, later renamed to SPIW - Special Purpose Individual Weapon. In teh mean time, some elements within Army also sponsored a more conventional approach to the same problem, and oredered development of conventional automatic rifles, firing ordinary small-caliber bullets. During late 1950s and early 1960s there was a lot of experimentation and development in regard of new ammunition, optimal calibers and rifle designs. The problem was, that widely promoted SPIW program seemed to have no end, and the recently adopted "full-power" 7.62mm M14 rifle faced serious production problems.
Enter the Armalite. In the year of 1957 The US Army requests the Armalite Division of the Fairchild Aircraft Corp to develop a rifle of .22 caliber, lightweight, select-fire, and capable to penetrate the standard steel helmet at 500 meters. The Eugene Stoner, then a designer at the Armalite, began to develop this rifle, based on his earlier design, 7.62mm AR-10 battle rifle. At the same time, experts at the Sierra Bullets and the Remington, in conjunction with Armalite, began do develop a new .22 caliber cartridge, based on the .222 Remington and .222 Remington Magnum hunting cartridges. This development, initially called the .222 Remington Special, was finally released as .223 Remington (metric designation 5.56x45mm). Next year Army tests new rifles, known as Ar-15, and rejects these in favor of the M14. Feeling that the Ar-15 rifle has poor chances to compete with the recently adopted M14 in the US Military, in 1959 the Fairchild Corp, a parent company of the Armalite, sells all rights and manufacturing documentation for this rifle to the Colt's Patent Firearms Manufacturing Company, which had long-time relations with US Military and proven track of selling military guns both in USA and abroad. Colt instantly begins aggresive marketing campaign for the new rifle, stressing its accuracy, low recoil, light weight and modern design. In the 1962, US DoD Advanced Research Projects Agency (ARPA) purchases 1000 AR-15 rifles from Colt and sends those rifles to the South Vietnam, for field trials. Same year brings glowing reports about the effectiveness of the new "black rifle", used by South Vietnamese forces.
Following the delays in introduction of the ill-fated 'next generation' SPIW system and production troubles with M14, in 1963 Colt receives contracts from US Government for 85 000 rifles for US Army (designated as XM16E1) and for further 19 000 rifles for US Air Forces (designated M16). The US AF M16 was no more than an AR-15 rifle with appropriate markings. The XM16E1 differed from AR-15/M16 by having an additional device, the so called "forward assist", which was used to manually push the bolt group in place in the case of jams. Next year US Air Forces officially adopted new rifle as M16. Same year US Army adopted the XM16E1 as a limited standard rifle, to fill the niche between discontinued 7.62mm M14 rifle and the forthcoming SPIW system (which newer got past the prototype and trial stages).
With rapidly growing presence of US troops in Vietnam, in 1966 US Government makes the first large purchase of the Ar-15 / M16 rifles, ordering 840 000 rifles for US Armed forces, worth almost $92 millions, and in 1967 US Army officially adopts the XM16E1 rifle as a standard "US Rifle, 5.56mm, M16A1".
During immediately following years, a number of negative reports apears from Vietnam. M16A1 rifles, issued to US troops in the Vietnam, severely jammed in combat, resulting in numerous casualties. There were some causes for malfunction. First of all, during the introduction of the new rifle and its ammunition into the service, US Army replaced originally specified Dupont IMR powder with standard ball powder, used in 7.62x51mm NATO ammunition. The ball powder produced much more fouling, that quickly jammed the actions of the M16 unless the gun was cleared well and often. It also had different pressure curve, resulting in increased stress on operating parts of the gun. This pitifully combined with the fact that the initial M16 rifles were promoted by the Colt as "low maintenance", so, for the sake of economy, no cleaning supplies were procured for new M16 rifles, and no weapon care training was conducted fro the troops. As a result, soldiers did not knew how to clean their rifles, and had no provisions for cleaning, and things soon turned bad. Another cost-saving measure on the part of the Army was to give up with cromium plation of the barrel bore and bolt group, which made these parts much more sensitive to corrosion and rust that originally designed.
After several dramatic reports in US press and Congressional investigation of the troubles, several actions were taken to remedy the problems. The 5.56mm ammunition was now loaded using different powders that produce much less residue in the gun action. The barrel, chamber and bolt of the rifles were chrome-lined to improve corrosion resistance. Cleaning kits were procured and issued to troops, and a special training programs were developed and conducted ever since. Earliest cleaning kits could be carried separate from rifle only, but since circa 1970 all M16A1 rifles were manufactured with the containment cavity in the buttstock, that held the cleaning kit. At the same time (circa 1970) the new 30 rounds magazines were introduced into service instead of the original 20 rounds ones, to equal Soviet and Chinese AK-47 assault rifles, which had 30-rounds magazines from the very beginning.
Therefore, by the end of the US involvment in Vietnam war, the M16A1 rifle eventually became more or less mature. It gradually replaced older rifles in US service, and also influenced the work on the small-caliber ammunition and automatic firearms in other countries, including the USSR. This work culminated in the NATO trials, held in 1977 - 79, with intent to adopt a small-caliber, high-velocity cartridge to replace the potent, but somehow overly powerful 7.62mm NATO round as standard infantry rifle ammunition for the whole NATO organisation. Not surprisingly, the winner of the trials was the american 5.56x45mm cartridge, although in a version loaded with Belgian SS109 bullet, which provided better long-range ballistics than the original US 5.56mm M193 ammo.
In 1981, Colt developed a variation of the M16A1, adapted for the SS109/5.56mm NATO cartridge, and submitted it to the military trials as the M16A1E1. This rifle differed from the M16A1 by having the heavier barrel with faster 1:7 rifling, a different type rear sights (adjustable for both range and windage), round handguards instead of triangular ones, and by replacing the full-auto fire mode with the burst (limited to 3 rounds per trigger pull), to preserve the ammunition. It was officially adopted by US DoD as the "US Rifle, 5.56mm, M16A2" in 1982, which still is the primary infantry rifle for US Armed forces and a number of other armies and law enforcement organizations.
The development of the M16 rifle continued. By the mid-1990s, Colt, at the request of the US Special Forces, produced a carbine version of the M16A2, designated M4. This carbine traces its roots back to the 1960s vintage Colt CAR-15 carbine, but has several improvements. Actually, it was the M16A2 rifle, fitted with a shorter barrel and handguards, with the gas port moved back. The fixed buttstock was replaced by a retractable telescoping buttstock, originally designed in the mid-1960s by a Colt employee, Robert E. Roy for the Colt “Commando” carbines. The M4 was supposed to become the standard US Special Forces rifle, and could be fitted with the standard M16A2-type bayonet and the M203 40mm grenade launcher.
By 1996, the two newest versions of the M16 appeared, the M16A3 and M16A4. These differ from the M16A2 by having a removable carrying handle, with the upper receiver being fitted with a Picatinny-type accessory rail. Otherwise the M16A4 is similar to the M16A2, while the M16A3 also replaced the infamous three-round burst mode with a full auto mode. The key advantage of both the M16A3 and A4 rifles is the ability to quickly mount and re-mount a wide variety of optical, red dot or night vision / IR sights with MIL-STD 1913 (Picatinny-type) compatible mounts. The M4 carbine was also upgraded to “flat top” configuration, which is now standard.
The M16 is still a general-issue rifle with the US Armed forces. It is also widely used by the US Law Enforcement agencies, either in military form (for example, the LAPD had some M16s, retired from the Army), or in "civilian" semi-automatic only form. The AR-15 style rifles are made in the USA by at least a dozen large companies, such as ArmaLite, Bushmaster, Colt, FN Manufacturing, Hesse, Les Baer, Olympic, Wilson Combat, and by a number of smaller companies, many of which assemble their rifles from components made by other major manufacturers. M16-type rifles are also manufactured outside the USA, most notably in Canada, by Diemaco Co (now Colt Canada). China also makes some AR-15 type rifles at the NORINCO state factories, known as CQ. M16 rifles are used by many foreign military groups, most notably the British SAS, who preferred the M16 over the infamous L85A1 rifle, and by many others.
At the present time almost all of the initial flaws of the M16 have been removed and it is considered among the best assault rifles in the world. While its reliability in harsh conditions cannot match that of its main rival, the Kalashnikov AK-47 and AK-74, it is still a quite reliable weapon, especially when well maintained. It is also comfortable to fire and quite accurate.
It must be noted that during recent operations in Afghanistan and Iraq (2002 and 2003, respectively), there were several controversial complaints about the effectiveness and reliability of the M16A2 and M4 rifles. It seems that most complaints about the reliability of the M16A2 rifles came from inadequate troop training and the resulting improper handling of the rifles. The M4 carbines are a somewhat different story, since the problems can be partially traced to the shortened gas system, which now operates at higher pressures, thus more violently. The M4 also rapidly overheated. Another general complaint was about the poor effectiveness of the standard M855 ammunition, which lacked stopping power especially from shorter M4 carbine barrels. To partially cure this problem, the US SOCOM recently issued a new type of 5.56 mm ammunition, the Mk.262 mod.0, which is loaded with heavier Sierra Match King bullets, weighing 4.99 gram compared with the 4.0 gram bullet in the M855 cartridge. The most recent experience also clearly showed the excessive length of the M16A2 rifles, which are too clumsy for motorised troops, riding in cars, armored carriers and helicopters. At the present time, many M16A2 rifles are being replaced in the hands of US troops with more compact and maneuverable M4A1 carbines.
One of the key advantages of the Stoner design, that must be especially stressed, is the extreme flexibility of the construction. At the present time the interchangeable complete upper receiver assemblies ("upper" in short) are available in various barrel lengths and profiles (from 7 to 24 inches long, slim and heavy), in dozens of rifle and pistol calibers (from tiny but fast .17 Remington and up to monstrous .458 SOCOM, and from .22LR and 9mm Luger up to mighty .50AE). Special, manually single-shot uppers are commercially available in the extremely powerful .50BMG (12.7x99mm) caliber. Various "lower receiver" assemblies offer a broad variety of trigger units, buttstocks and other options. This advantage is viable for both military (especially Spec Ops), Law Enforcement, and civilian applications, as it allows to tailor any particular AR-15 type rifle to the current situation and tactical needs.
M16 / AR-15 Technical description
The original AR-15 rifle is a gas operated, selective fire, magazine fed weapon. Every rifle from the M16 family is generally the same, but most civilian AR-15 type rifles are semi-automatic only.
The heart of the AR-15 is the direct gas system, developed by the Eugene Stoner in the early 1950s. This system uses no conventional gas piston and rod to propel bolt group back after the shot is fired. Instead, the hot powder gases are fed from the barrel and down to the stainless steel tube into the receiver. Inside the receiver, the rear end of the gas tube enters into the "gas key", a small attachment on the top of the bolt carrier. The hot gases, through the gas key, enter the hollow cavity inside the bolt carrier, and expands there, acting against the bolt carrier and the collar around the bolt body. The pressure of the gases causes the bolt carrier to move back against initially stationary bolt. The linear rearward movement of the carrier initially transferred into the rotation of the bolt, via the cam slot in the bolt carrier and the cam pin, attached to the bolt, that followed the slot. As soon as the bolt is rotated to unlock from the barrel, the bolt group continues its rearward travel under the inertia and the residual pressure in the barrel, extracting the spent case and compressing the buffer return spring, located in the buttstock. The forward movement of the bolt group first strips the fresh cartridge from the magazine and, on the final stage of the movement, rotates the bolt to lock into the barrel extension. The bolt has 7 radial locking lugs, eight lug is located on the extractor claw. Since the introduction of the XM16E1 rifle, the forward assist device is used on all military and most civilian AR-15 type rifles. This device consist of the spring-loaded button with internal claw, that engages the serrations on the right side of the bolt carrier to push it forward, if the pressure of the return spring is insufficient to do so (for example, due to the fouling inside the receiver or chamber). The rifle will not fire unless the bolt is locked and the bolt carrier is in its forwardmost position. The bolt carrier and the bolt itself are chrome-plated. Another feature of the AR-15 type rifles is the bolt catch device, that locks the bolt group in the open position when the last round is fired. To release the bolt group one must push the button, located at the left side of the receiver, above the magazine. The "T"-shaped cocking handle is located at the rear of the receiver, above the buttstock, and does not reciprocate when gun is fired.
The trigger/hammer group is basically similar to one, found in M1 Garand rifle, and, actually, traces its roots back to the early 1900s, when the great John M. Browning developed his famous Auto-5 semiautomatic shotgun. This basically consists of a hammer, a trigger, a disconnector, a full auto sear and some springs. The fire selector / safety switch is located at the left side of the receiver, above the pistol grip, and is easily operated by the right hand thumb. This switch has 3 positions: "safe", "semi" (single shots), and "auto" (full automatic on M16A1 and M16A3 rifles) or "burst" (3 rounds bursts, on M16A2 and M16A4). In the latter case (on the M16A2 and M16A4 rifles), the trigger unit also includes the ratchet device to count the shots fired.
The ejection port is located at the right side of the receiver, and is closed by the spring-loaded dust cover, which automatically pops open when bolt carrier is pulled back. The M16A2 also featured the spent case deflector - a triangular bulb on the receiver, just behind the ejection port, that allows the gun to be safely fired left-handed.
The M16 is fed using box magazines. Earliest magazines were made from aluminum and held 20 rounds. Circa 1970 the new, 30 rounds magazines were introduced into service and these magazines are still in service now. An extremely wide variety of magazines available on the commercial marked, starting from the "US post-ban" 5 and 10 round magazines, and up to 40-rounds box, 90-rounds helical, 100-rounds dual drums (Beta-C) and 120-rounds single drums.
The receiver is made from aluminum alloy, and consists of two parts - "upper receiver" and "lower receiver" (sometimes referred simply as "upper" and "lower"). Most receivers are made from aluminum forgings by machining, but some commercially available receivers are made from aluminum castings with final drilling and machining. The upper and lower receivers are linked by two cross-pins - one at the front (pivot pin), and one at the rear, above the pistol grip (takedown pin). To field strip the AR-15, one must push the rear pin to the right as far as it will go, and then hinge the upper receiver around the front pin. This will allow the bolt group and the carrying handle to be removed from the upper receiver. For further disassembly, the front pin also must be pushed out, and the upper and lover receiver can be separated. The key benefit of this design is the great flexibility - if all components available are made to the same specifications (in most cases they are), one can easily swap various upper receivers on one lower receiver and vice versa. Since the complete "upper" module consist also of the bolt group and the barrel with the gas system, one can easily have different barrel lengths, styles (light, heavy, fluted, bull), and even calibers, for one "lower" group, that consists of the lower receiver with the trigger/hammer unit, recoil buffer, pistol grip and the buttstock.
The furniture on military rifles is made from the black plastic, hence the common name "the black rifle". On the early AR-15 and M16A1 rifles, the handguards were of triangular cross-section, and were made from two non-interchangeable parts. On the M16A2 and latter rifles, the handguards are of round cross-section, and have two interchangeable upper-lower sections. The buttstock on the M16A2 is similar in design to one of M16A1, but slightly longer. The one disadvantage of the Stoner system is that it can not be adapted for conventional folding buttstock. Instead, if required, a telescoped stock is used, that allows to shorten the rifle when required by about the half of the length of the standard stock. M16 is usually equipped with sling, and can accept a knife - bayonet, either an old style M7, or a newer style M9. The flash hiders on the earliest AR-15s and M16s were prong-type, with three open slots, but later were replaced with "bird-cage" flash hiders with four (M16A1) or five (M16A2) slots.
Both M16A1 and M16A2 can be equipped with underbarrel 40mm M203 grenade launcher. M203 mount replaces the standard handguards on the rifle and requires a grenade launcher sight to be mounted on the carrying handle.
Standard sights of the M16A1 consist of a protected front post, mounted on the gas block, and of an aperture flip-up rear, with 2 range settings. Rear sights are mounted within the carrying handle and are adjustable for windage. The A2 style rear sight also features an flip-up, dual aperture sights, with one smaller aperture for daylight usage, and another larger aperture for low light conditions. The range adjustments are made by the rotating knob, located just under the sight. The front sight is generally the same as on the M16A1. The M16A3 and A4 rifles have detachable carrying handles with A2 sights, and the Picatinny-type MilStd rail on the top of the receiver, that can accept a wide variety of sighting devices and mounts. The most common military sighting equipment beyond basic iron sights is an Trijicon ACOG low-magnification telescope or Aimpoint or EOTech 1X magnification red-dot sight, often complemented by removable back-up iron sights (BUIS), installed on the same Picatinny rail.
The original AR-15 rifle is a gas operated, selective fire, magazine fed weapon. Every rifle from the M16 family is generally the same, but most civilian AR-15 type rifles are semi-automatic only.
The heart of the AR-15 is the direct gas system, developed by the Eugene Stoner in the early 1950s. This system uses no conventional gas piston and rod to propel bolt group back after the shot is fired. Instead, the hot powder gases are fed from the barrel and down to the stainless steel tube into the receiver. Inside the receiver, the rear end of the gas tube enters into the "gas key", a small attachment on the top of the bolt carrier. The hot gases, through the gas key, enter the hollow cavity inside the bolt carrier, and expands there, acting against the bolt carrier and the collar around the bolt body. The pressure of the gases causes the bolt carrier to move back against initially stationary bolt. The linear rearward movement of the carrier initially transferred into the rotation of the bolt, via the cam slot in the bolt carrier and the cam pin, attached to the bolt, that followed the slot. As soon as the bolt is rotated to unlock from the barrel, the bolt group continues its rearward travel under the inertia and the residual pressure in the barrel, extracting the spent case and compressing the buffer return spring, located in the buttstock. The forward movement of the bolt group first strips the fresh cartridge from the magazine and, on the final stage of the movement, rotates the bolt to lock into the barrel extension. The bolt has 7 radial locking lugs, eight lug is located on the extractor claw. Since the introduction of the XM16E1 rifle, the forward assist device is used on all military and most civilian AR-15 type rifles. This device consist of the spring-loaded button with internal claw, that engages the serrations on the right side of the bolt carrier to push it forward, if the pressure of the return spring is insufficient to do so (for example, due to the fouling inside the receiver or chamber). The rifle will not fire unless the bolt is locked and the bolt carrier is in its forwardmost position. The bolt carrier and the bolt itself are chrome-plated. Another feature of the AR-15 type rifles is the bolt catch device, that locks the bolt group in the open position when the last round is fired. To release the bolt group one must push the button, located at the left side of the receiver, above the magazine. The "T"-shaped cocking handle is located at the rear of the receiver, above the buttstock, and does not reciprocate when gun is fired.
The trigger/hammer group is basically similar to one, found in M1 Garand rifle, and, actually, traces its roots back to the early 1900s, when the great John M. Browning developed his famous Auto-5 semiautomatic shotgun. This basically consists of a hammer, a trigger, a disconnector, a full auto sear and some springs. The fire selector / safety switch is located at the left side of the receiver, above the pistol grip, and is easily operated by the right hand thumb. This switch has 3 positions: "safe", "semi" (single shots), and "auto" (full automatic on M16A1 and M16A3 rifles) or "burst" (3 rounds bursts, on M16A2 and M16A4). In the latter case (on the M16A2 and M16A4 rifles), the trigger unit also includes the ratchet device to count the shots fired.
The ejection port is located at the right side of the receiver, and is closed by the spring-loaded dust cover, which automatically pops open when bolt carrier is pulled back. The M16A2 also featured the spent case deflector - a triangular bulb on the receiver, just behind the ejection port, that allows the gun to be safely fired left-handed.
The M16 is fed using box magazines. Earliest magazines were made from aluminum and held 20 rounds. Circa 1970 the new, 30 rounds magazines were introduced into service and these magazines are still in service now. An extremely wide variety of magazines available on the commercial marked, starting from the "US post-ban" 5 and 10 round magazines, and up to 40-rounds box, 90-rounds helical, 100-rounds dual drums (Beta-C) and 120-rounds single drums.
The receiver is made from aluminum alloy, and consists of two parts - "upper receiver" and "lower receiver" (sometimes referred simply as "upper" and "lower"). Most receivers are made from aluminum forgings by machining, but some commercially available receivers are made from aluminum castings with final drilling and machining. The upper and lower receivers are linked by two cross-pins - one at the front (pivot pin), and one at the rear, above the pistol grip (takedown pin). To field strip the AR-15, one must push the rear pin to the right as far as it will go, and then hinge the upper receiver around the front pin. This will allow the bolt group and the carrying handle to be removed from the upper receiver. For further disassembly, the front pin also must be pushed out, and the upper and lover receiver can be separated. The key benefit of this design is the great flexibility - if all components available are made to the same specifications (in most cases they are), one can easily swap various upper receivers on one lower receiver and vice versa. Since the complete "upper" module consist also of the bolt group and the barrel with the gas system, one can easily have different barrel lengths, styles (light, heavy, fluted, bull), and even calibers, for one "lower" group, that consists of the lower receiver with the trigger/hammer unit, recoil buffer, pistol grip and the buttstock.
The furniture on military rifles is made from the black plastic, hence the common name "the black rifle". On the early AR-15 and M16A1 rifles, the handguards were of triangular cross-section, and were made from two non-interchangeable parts. On the M16A2 and latter rifles, the handguards are of round cross-section, and have two interchangeable upper-lower sections. The buttstock on the M16A2 is similar in design to one of M16A1, but slightly longer. The one disadvantage of the Stoner system is that it can not be adapted for conventional folding buttstock. Instead, if required, a telescoped stock is used, that allows to shorten the rifle when required by about the half of the length of the standard stock. M16 is usually equipped with sling, and can accept a knife - bayonet, either an old style M7, or a newer style M9. The flash hiders on the earliest AR-15s and M16s were prong-type, with three open slots, but later were replaced with "bird-cage" flash hiders with four (M16A1) or five (M16A2) slots.
Both M16A1 and M16A2 can be equipped with underbarrel 40mm M203 grenade launcher. M203 mount replaces the standard handguards on the rifle and requires a grenade launcher sight to be mounted on the carrying handle.
Standard sights of the M16A1 consist of a protected front post, mounted on the gas block, and of an aperture flip-up rear, with 2 range settings. Rear sights are mounted within the carrying handle and are adjustable for windage. The A2 style rear sight also features an flip-up, dual aperture sights, with one smaller aperture for daylight usage, and another larger aperture for low light conditions. The range adjustments are made by the rotating knob, located just under the sight. The front sight is generally the same as on the M16A1. The M16A3 and A4 rifles have detachable carrying handles with A2 sights, and the Picatinny-type MilStd rail on the top of the receiver, that can accept a wide variety of sighting devices and mounts. The most common military sighting equipment beyond basic iron sights is an Trijicon ACOG low-magnification telescope or Aimpoint or EOTech 1X magnification red-dot sight, often complemented by removable back-up iron sights (BUIS), installed on the same Picatinny rail.
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