ArmaLite AR - 18 The AR - 18 is a gas operated , selective fire assault rifle chambered for 5 . 56x45mm ammunition . The AR - 18 was designed at ArmaLite in California by Arthur Miller , George Sullivan , and Charles Dorchester in 1963 as an improved alternative to the AR - 15 design , which had just been selected by the U . S . military as the M16 . While the AR - 18 was never adopted as the standard service rifle of any nation , its production licence was sold to companies in Japan and England , and it is said to have influenced many later weapons such as the British SA80 , the Singaporean SAR - 80 and SR - 88 , the Austrian Steyr AUG , and the Heckler and Koch G36 . It gained some notoriety through its use by the Provisional IRA , which allegedly christened it the " Widowmaker " . Background . Soon after the adoption of the 7 . 62x51mm NATO M14 rifle in 1957 , the U . S . Army ' s Continental Army Command ( CONARC ) began an investigation of Small Caliber High Velocity ( SCHV ) rifles as an off - shoot of the military ' s existing research program , Project SALVO . ArmaLite and Winchester Arms were solicited by CONARC to provide prototype automatic rifles chambered for high velocity centerfire . 22 rounds . ArmaLite ' s AR - 15 was a scaled down version of the 7 . 62mm AR - 10 , which had appeared too late to be a serious contender against the M14 for adoption by the US Army . Its competitor was the Winchester . 224 Light Rifle , a ' Carbine ' Williams prototype carbine design re - made in a . 22 high velocty round which was similar to , but not interchangeable with , the . 223 Remington ( 5 . 56x45mm ) . Construction and design . Overall , the new AR - 18 rifle was much more conventional than previous ArmaLite designs , although it used the relatively new stamped steel construction from its predecessor , the AR - 16 . Despite being pioneered by the Germans during WW2 in weapons such as the MP44 , and later adopted for the AKM , the use of stamped and welded sheet metal components was still uncommon in the manufacture of military rifles in the West in the early 1960s , which had , until then , largely retained the use of traditional machined forgings . Compared to the smooth lines of the AR - 15 , the AR - 18 faced criticism over its stamped and welded construction , which had demonstrably greater tolerances in parts fit . However , the rifle proved to be both reliable and very accurate at all ranges up to . Its simple construction promised significantly reduced production costs , and allowed it to be licence - produced locally on less advanced machinery , potentially reducing dependence on foreign manufacturers . Moreover , the gas piston operation of the AR - 18 proved much more resistant to carbon fouling than the direct gas impingement system of the earlier AR - 10 and AR - 15 rifles , as it did not vent gas and carbon particles directly into the receiver . The AR - 18 ' s action was powered by a short - stroke gas piston above the barrel . The gas piston was of 3 - piece design to facilitate disassembly , with a hollow forward section with 4 radial gas vent holes fitting around a stainless steel gas block projecting rearwards from the foresight housing . The gas was vented from the barrel and travelled via a vent through the foresight housing into the hollow front section of the piston , which caused it to move rearwards a short distance . The rear end of the piston emerged through the barrel extension to contact the forward face of the bolt carrier , causing it in turn to move rearwards . The bolt itself was of similar configuration to the AR - 15 with 7 radial locking lugs engaging corresponding recesses in the barrel extension , and the extractor in place of the 8th lug . The bolt was moved into and out of the locked position via a cam pin that engaged a helical slot in the bolt carrier , which rode on two metal guide rods ( each with its own return spring ) instead of contacting the receiver walls , providing additional clearance for foreign matter entering the receiver . Unlike the AR - 15 , the cocking handle fitted directly into a recess in the bolt carrier and reciprocated with it during firing , allowing the firer to force the breech closed or open if necessary . The cocking handle slot had a spring - loaded cover that could be closed by the user to prevent debris entering the receiver , and it would open automatically as the bolt carrier moved rearwards after the first shot . The recoil springs were housed within the receiver , differing from the AR - 15 which housed its more elaborate 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 ) . The sights were of similar design and sight picture to those of the AR - 15 - a 2 - position flip aperture rear sight and post foresight - but the rear sight was made of stampings . A notable change is the use of a more conventional lower sight line closer to the axis of the bore , in contrast to the elevated sights of the AR - 15 . A dovetail was spot welded to the receiver in front of the rear sight for a proprietary ArmaLite quick - detachable scope mount . Overall , the design is simple and effective with some clever touches ; for example the bolt guide rod assembly guides the bolt in the receiver , retains the recoil springs and the rear end of the top handguard , as well as serving as the latch holding the upper and lower receivers together in the closed position . Disassembly is somewhat similar to the AR - 15 , with the working parts accessed by the rifle pivoting open on a cross - pin immediately forward of the magazine well . History . M16 . During the protracted U . S . military trials of the AR - 15 , ArmaLite ' s corporate owners Fairchild essentially gave up on the design , and sold the AR - 15 production rights to Colt . Fairchild also spun off ArmaLite as an independent company , allowing the new owners to buy all of the company ' s designs except for the AR - 10 and AR - 15 . When the U . S . military ultimately selected the AR - 15 as the M16 , ArmaLite could no longer profit from its adoption . AR - 16 . The AR - 16 appeared in the later 1950s . The AR - 16 , a 7 . 62mm NATO selective - fire rifle , was Eugene Stoner ' s final design for ArmaLite . The AR - 16 and its predecessor , the AR - 12 were designed by Stoner in response to demands by the military forces of smaller , less developed nations for a less expensive , yet state - of - the - art selective - fire military rifle that unlike the AR - 10 and AR - 15 , could be produced inexpensively of heavy - gauge sheet metal using automatic screw machines , lathes , and presses . The AR - 12 originally featured a direct - impingement ( DI ) gas operation system , but this was changed to a more conventional short - stroke gas piston in the AR - 16 after ArmaLite sold the production rights to the DI system to Colt Firearms . The AR - 16 had a short , 15 - inch barrel , hinged wooden butt , and weighed 8 . 75 pounds empty ; only three examples were built . Eugene Stoner left ArmaLite in 1961 , shortly before Fairchild divested itself of ownership . AR - 18 . The U . S . military ' s later adoption of the AR - 15 gave legitimacy to its 5 . 56mm cartridge , and ArmaLite sought to develop a competing design chambered in 5 . 56mm that did not infringe on the Colt licence agreement . With Stoner gone , it was decided to scale down the AR - 16 , and ArmaLite ' s new chief designer , Arthur Miller , embarked on the project . The resulting 5 . 56mm design appeared in 1963 and was named the AR - 18 . Miller later received for the rifle in 1969 . Production and operational use . The AR - 18 was put into limited production at ArmaLite ' s machine shop and offices in Costa Mesa , California . A semi - automatic version of the AR - 18 known as the AR - 180 was later produced for the civilian market between 1969 and 1972 . ArmaLite was never equipped to build small arms on a production basis , and the Costa Mesa AR - 18 and AR - 180 rifles frequently show evidence of hand - fitting . A production license was granted to Nederlandsche Wapen - en Munitiefabriek ( NWM ) of Den Bosch , the Netherlands , but it is doubtful that any AR - 18 rifles were actually produced there . A license to produce the AR - 18 / 180 was then sold to Howa Machinery Co . , of Japan , and the rifle was produced there from 1970 until 1974 , when new controls on export of military arms by the Japanese government forced the company to cease all small arms production . From 1975 until 1983 , the Sterling Armaments Company of Dagenham , Essex , in the United Kingdom produced the AR - 18 / AR - 180 . Unlike the AR - 15 / M16 , the AR - 18 did not see substantial sales success , and was never officially adopted by any country as their standard service rifle . The reasons for this are unclear , but may have had something to do with the existing sales popularity of the AR - 15 / M - 16 , as well as the need for additional field testing and evaluation of the Costa Mesa - produced rifles , which were still in the advanced prototype stage . The AR - 18 was purchased for evaluation trials by various armed forces , including the United States ( 1964 ) and the United Kingdom ( 1966 ) . These suffered various malfunctions during evaluation trials by various nations . During the US trials at Aberdeen Proving Grounds in 1964 , the AR - 18 ' s functioning was found to vary from lot to lot of ammunition . The evaluating board concluded that while the basic design of the AR - 18 was sound , it required additional minor revisions and changes to improve safety and reliability before it could be considered for adoption as a service rifle . The British Ministry of Defence ( MOD ) tested the AR - 18 in March 1966 , and found the design unsatisfactory in performance during mud and sand trials . ArmaLite made several minor production modifications to the design commencing in 1965 , and the U . S . Army was directed to re - evaluate the AR - 18 at the end of 1969 . Testing was conducted at Aberdeen Proving Grounds , conducted by arsenal employees and the Infantry Board at Fort Benning , Georgia . However , American procurement officials were not interested in acquiring yet another 5 . 56 mm service rifle . Instead , the AR - 180 was sold on the civilian market , while the AR - 18 sold in small quantities to police and law enforcement organizations , as well as armies and security forces of nations such as Botswana , Haiti , and Swaziland . Still others found their way into the hands of terrorist or paramilitary groups , such as the Provisional IRA in Northern Ireland . In 1968 , dissatisfied with efforts to market the AR - 18 , Arthur Miller left ArmaLite . Variants . The standard AR - 18 versions manufactured by ArmaLite , Howa and Sterling differ only in minor details . Rifles were normally equipped with sling , cleaning kit ( bore / brush ) , and a knife - type bayonet with scabbard . An optional bipod with case was available . The AR - 180 was capable of semi - automatic fire only and was externally identical in appearance to the AR - 18 with one exception ; the selector had only 2 positions , omitting the third " AUTO " position found on the AR - 18 . Sterling manufactured a small number of sporter variants called the AR - 180 SCS , of which only 385 were reputed to have been made . It had a large single - piece wooden thumbhole stock that replaced the butt , pistol grip and handguard of conventional versions . The metal parts differ in the lack of the ejection port cover , a PH prefix to the serial number and adapted safety and magazine release controls . Sterling also manufactured small numbers of a short version , the AR - 18S . This version used the same basic mechanism and folding butt , but had a barrel and a length of with the butt extended . The shortened barrel was fitted with a cone - shaped flash suppressor to address the additional muzzle flash resulting from the short barrel . Some examples had an additional pistol grip fitted to the underside of the handguard . A 2 . 75 X 20 mm telescopic sight was available but few were sold . It was marked " ArmaLite " , and had a quick - detachable , see - through mount that attached to an integral dovetail spot - welded to the top of the receiver . Also of note is that bullpup conversions of the AR - 18 and the Stoner 63 were fabricated by Enfield , the rival company of Sterling Armaments Ltd when developing the SA80 . Recent developments . The ArmaLite brand was purchased in 1996 by Eagle Arms , a small U . S . 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 molded 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 , and the deletion of the original AR - 18 / 180 spring - loaded dust cover for the cocking handle slot . 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 / M16 magazines . An AR - 180B version with a Picatinny rail is planned for production . As of 2007 production has been put on hold due to sluggish sales and lacking profits , along with the fact that the polymer lower receiver is no longer produced .