While the AR-18 was never adopted as the standard service rifle of any nation, its production license was sold to companies in Japan and the United Kingdom, and it is said to have influenced many later weapons such as the British SA80,[1][2][3] the Singaporean SAR-80 and SR-88,[3] the Belgian FN F2000,[4] the Japanese Howa Type 89[5] and the German Heckler and Koch G36.

ArmaLite and Winchester Arms were solicited by CONARC to provide prototype automatic rifles chambered for high-velocity centerfire .22 rounds.

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.

[12] 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 license agreement.

Despite being pioneered by the Germans during WW2 in weapons such as the MP 44, and later adopted for the Soviet 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.

[13] Compared to the smooth lines of the AR-15, which had demonstrably finer tolerances in parts fit, the AR-18 faced criticism over its stamped and welded construction.

The rear end of the piston emerges through the barrel extension to contact the forward face of the bolt carrier, causing it in turn to move rearwards.

[6] The bolt is moved into and out of the locked position via a cam pin that engaged a helical slot in the bolt carrier, which rides 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.

[16] Unlike the AR-15, the cocking handle fits directly into a recess in the bolt carrier and reciprocates with it during firing, allowing the firer to force the breech closed or open if necessary.

The cocking handle slot has a spring-loaded cover that can be closed by the user to prevent debris entering the receiver, and it will open automatically as the bolt carrier moves rearwards after the first shot.

A dovetail is spot welded to the receiver in front of the rear sight for a proprietary ArmaLite quick-detachable scope mount.

The original magazines made by ArmaLite and Howa were of gray anodized aluminum alloy with black plastic followers and came in 5- and 20-round capacities.

A plastic copy of the fixed folding metal bipod issued with the early M-16 was available and came in a similar protective case.

AR-180 users were leery of buying a non-adjustable bipod made of thermoset plastic so few were sold, making it a rare accessory today.

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 hinge pin immediately forward of the magazine well.

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.

[13] Between 1975 and 1978, there was a brief pause in production as ArmaLite was finalizing an agreement with Sterling Armaments Company, United Kingdom to produce the rifle under license.

[17] Production plans for the AR Series 100 would fail to push through as Elisco would be dissolved and its assets liquidated in the late 1980s.

The reasons for this are unclear, but may have had something to do with the existing sales popularity of the AR-15/M16, 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.

[18] 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.

[18] 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.

[citation needed] Towards the end of AR-180 production at ArmaLite's Costa Mesa shop in 1972, some unused AR-18 lowers were used to assemble AR-180s.

[24] It has a large single-piece wooden thumbhole stock that replaces 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.

It is marked "ArmaLite", and has a quick-detachable, see-through mount that attaches to an integral dovetail spot-welded to the top of the receiver.

A delayed-blowback upper was also developed by Ross Rudd using a hesitation lock but not manufactured due to financial backing reasons.

[34] When the AR-18 was designed, a plethora of different methods of gas and recoil operation existed in self-loading intermediate caliber rifles.