Type Assault Rifle
Place of origin United States
In service None
Used by See Users
Designer Gene Stoner (AR-16), Arthur Miller
Manufacturer Armalite (US), HOWA Machinery Co. (Japan), Sterling Armaments Company. (UK)
Variants AR-18S, AR-180, AR-180B—foreign designs based upon the AR-18 include the British SAR-87, Singaporean SAR-80 and the Japanese Howa Type 89; bullpup adaptations include the British SA-80 and the Australian Bushmaster M17S
Weight 6.6 lb (3 kg) (empty)
Length 38 in (965 mm)
Barrel length 18 in (457 mm)
Cartridge 5.56x45mm NATO
Action Gas operated, rotating bolt
Rate of fire 700–800 rounds/min
Muzzle velocity 3,250 ft/s (991 m/s)
Feed system 20, 30, or 40-round box magazine
Sights Iron or removable 3× scope
The AR-18 is a gas operated, selective fire assault rifle chambered for 5.56x45mm NATO ammunition. The AR-18 was designed at ArmaLite in California by Arthur Miller, George Sullivan, and Charles Dorchester in 1963 as an improved 5.56 mm caliber alternative to Armalite's previous AR-15 design, for which production rights had been sold to Colt. Armalite's interest in the design waned when the Colt AR-15 was selected for production by the U.S. Army as the M16. While it was never adopted as the standard service rifle of any nation, it has influenced many later weapons such as the British SA80, the Singaporean SAR-80 and SR-88, and the Heckler and Koch G36. It gained some notoriety through its use by the IRA, who allegedly christened it the "Widowmaker".
In 1955, the US Army was holding trials for a battle rifle to replace their M1 Garands with a new weapon capable of fully automatic fire. The new weapon was intended to either fully or partially replace the M1 Carbine, Browning Automatic Rifle (BAR), and M3 Submachinegun as well. The US Army was against any reduction in power in their new weapon despite arguments that the full power round was not suitable for automatic fire and through their dominant position a slightly shorter version with similar power to their current rifle round became the standard 7.62x51mm NATO round. Springfield Armory and Fabrique Nationale both entered designs based on fairly conventional engineering; the M14 was selected. This rifle replaced the Garand, but was essentially a product-improved M1 Garand.
Eugene Stoner's ArmaLite 7.62x51mm AR-10 came too late in the evaluation for serious consideration, but his advanced design was a dramatic improvement on conventional thinking. Using a number of advanced features and materials, the AR-10 was almost two pounds lighter than the M14. One of the most novel concepts of the AR-10 was a composition aluminum/steel barrel. Unfortunately during endurance testing of the AR-10 at Springfield Armory, an AR-10 suffered a burst barrel. ArmaLite realized a change was in order, and switched to a steel barrel, but it was too late. The M14 won the selection process over both the AR-10 and the Belgian FAL rifle, but the M14's victory would be short lived. The Army quickly learned that a full power 7.62 mm rifle fired on full auto was an uncontrollable beast. With the United States involvement in the close quarters jungle fighting of Vietnam, a lighter rifle with increased firepower and capacity was desired.
Only two years later, the US Army was once again looking for a new rifle, this time based on a much smaller .22 caliber round and lighter in weight. This time, ArmaLite was invited to compete right from the start, and responded with a smaller version of the AR-10, the AR-15. Winchester Arms submitted a remake of a 'Carbine' Williams prototype carbine, and Springfield Armory was forbidden to participate, as senior Ordnance Corps officials had not yet accepted the small-caliber, high-velocity concept.
In the end the Army selected the AR-15, as the M16, as their new standard rifle. This was not without further controversy, especially early reports of problems with the gas system fouling. Although these problems were later traced to changes in the ammunition and an almost complete lack of cleaning in the field, it was often used as evidence against the weapon itself. During the protracted acceptance trials (which took several years) ArmaLite had essentially given up, and sold the AR-15 production license to Colt.
AR-16 and AR-18
After selling the design, ArmaLite began the development of two new rifles based on a modified action that no longer used a direct gas impingement action and were less prone to the fouling problems of the AR-15. The new design was intended to be easier to manufacture than the complex alloy forgings of the AR-15, in order to allow licensed manufacture while requiring easily-available tooling and less specialised expertise. The AR-16 was a 7.62 mm rifle similar to the AR-10, and the AR-18 was its 5.56 mm counterpart. The scaling down of the AR-16 to the AR-18 is mainly credited to ArmaLite's chief designer at the time, Arthur Miller who received U.S. Patent 3,246,567 for the rifle in 1969.
Overall, the new designs were much more conventional than previous ArmaLite designs. They were immediately criticized for their appearance. At the time, crude sheet metal and welded components were frowned upon in the use of service rifles. However, such construction proved to be a sign of things to come, as it promised significantly reduced production costs, and allowed it to be made on less advanced machinery. Moreover, the gas piston operation of the AR-18 proved much more resistant to fouling than that of the earlier AR-15 and M16 rifles.
Construction and design
Key to the cost reduction was the use of stamped-metal receivers and other components, as opposed to the AR-10/15's forged aluminum receiver. In addition a simpler operating system with a conventional short-stroke gas piston was selected in place of the lightweight direct gas tube and cutoff used in the earlier AR-15, intended to address complaints about reliability and fouling. The bolt, springs and recoil buffer were housed within the receiver, and the bolt rode on two metal rods instead of the receiver walls, which provided additional clearance for dust and mud. Compared to the AR-15, which housed its buffer mechanism in the buttstock, the AR-18's compact design enabled the use of a side-folding stock with a hinging mechanism (that later proved to be less than adequately rigid).
Armalite's AR-16 design never progressed beyond prototype stage, but the AR-18 was put into limited production, and underwent testing as an alternative to the AR-15. At this point, however, the AR-15/M16 rifle had been fully developed, flaws had been ironed out in successive modifications, and the U.S. military was not interested in acquiring yet another 5.56 mm service rifle. A semi-automatic version of the AR-18 design known as the AR-180 was later produced for the civilian market between 1969 and 1972 at Armalite's Costa Mesa manufacturing plant. The Costa Mesa AR-180s were one of the first military-type semi-automatic rifles to become widely available in the USA. Howa, of Japan, continued production of the AR-18/AR-180 from 1972 until 1974, but the Japanese government later forbade them to make war weapons, eventually axing the production. Sterling Armament Company of Dagenham in the UK produced the AR-18/AR-180 from 1976 to the mid 1980s and also as part of the ill fated but reliable SAR-87 concept. Parts from the AR-18 were used in the British forces' SA80, and the Singaporean SAR-80.
Use by the IRA
Many UK-made Sterling rifles were purchased by IRA sympathizers, and found their way into the hands of the Provisional IRA, where the rifle was known as the "widowmaker" (see also Provisional IRA arms importation). The Armalite rifle was for many years the most lethal weapon available to the PIRA. For this reason it become an iconic symbol within that movement. The Republican ballad "Little Armalite" tells of how the AR-18 changed the fortunes of Republican freedom fighters in their war with Britain. The 1980s Republican political strategy of parallel political and paramilitary campaigns was also christened the "Armalite and ballot box strategy".
Unlike the AR-15/M16, the AR-18 did not see substantial development over its life, and was not adopted in large numbers by any military service. In the end, the commercial failure of the AR-18 was not due to any significant flaws in its basic design, but in the lack of marketing efforts by ArmaLite. In 1968, dissatisfied with the way ArmaLite had marketed the AR-18, Arthur Miller left ArmaLite.
 Recent Developments
The ArmaLite brand was purchased in 1996 by Eagle Arms, a small US arms manufacturer, who adopted the Armalite brand for their company. An updated model of the AR-180 was introduced in 2001 as the AR-180B, with a moulded polymer lower receiver replacing the stamped steel original. The new lower receiver is combined with the buttstock, which is fixed on the AR-180B, instead of the side-folding butt on the original AR-18 and AR-180. Other AR-180B changes  include the use of standard AR-15 trigger group and rear sight parts. The AR-15 magazine release is also used, in contrast to the original AR-18 which had a different magazine release and corresponding slot in the body of the magazine, meaning AR-15 magazines needed a new slot cut to fit properly in the AR-18. As a result the AR-180B uses standard AR-15/M-16 magazines. An AR-180B version with a Picatinny rail is planned for production.
Although this rifle was not officially adopted by any nation as a standard service rifle, it was used for trials and some found their way into the hands of insurgents in Ireland among other places, and were sold to civil users and on the international arms market. The AR-18 was purchased by various armed forces for evaluation by the United States, the United Kingdom and elsewhere.