When first introduced in 1956, the AR-10 used an innovative combination of a straight-line barrel/stock design with phenolic composite, a new patent-filed gas-operated bolt and carrier system and forged alloy parts resulting in a small arm significantly easier to control in automatic fire and over 1 lb (0.45 kg) lighter than other infantry rifles of the day.

[2] In 1959, ArmaLite sold its rights to the AR-10 and AR-15 to Colt's Manufacturing Company due to financial difficulties, and limitations in terms of manpower and production capacity.

Sullivan leased a small machine shop in Hollywood, California,[8] hired several employees, and began work on a prototype for a lightweight survival rifle for use by downed aircrew.

Springfield Armory's T44E4 and heavier T44E5 were essentially updated versions of the Garand chambered for the new 7.62 mm round, while Fabrique Nationale submitted their FN FAL as the T48.

ArmaLite's AR-10 entered the competition late, hurriedly submitting two hand-built "production" AR-10 rifles based on the fourth prototype in the fall of 1956 to the United States Army's Springfield Armory for testing.

[11] The AR-10 prototypes (four in all) featured a straight-line stock design, rugged elevated sights, an oversized aluminum[12] flash suppressor and recoil compensator, and an adjustable gas system.

That same year, ArmaLite completed about 50 production AR-10 rifles at its workshop for use as demonstrator models for its sales agents, including Samuel Cummings, a famous international arms dealer.

[17] Attempts to rush completion of these fifty rifles resulted in a few units that were assembled with improperly machined barrel extensions, a defect that went unnoticed at the time.

The remaining Hollywood rifles were inspected and refitted as necessary with new parts to prevent the reoccurrence of the bolt lug failure, but the Nicaraguan order was lost for good.

product improvement requests, including an adjustable regulator, a repositioned gas tube, and a new three-prong flash suppressor.

[23] All AR-10s, whether produced by ArmaLite or by A.I., used the same Stoner-designed 20-round lightweight aluminum 'waffle' magazine with pressed-in, corrugated sides, intended to be discarded in combat once emptied.

Germany, Austria, the Netherlands, Finland, and South Africa also purchased small numbers of the AR-10 for test purposes, and Cuba's Batista government ordered 100 "Transitional" model rifles in 1958.

The Cuban order was delivered to Havana, but in December 1958 Fidel Castro's forces took control of the country, including the warehouse containing the AR-10 shipment.

[25] However, rapidly worsening relations with the United States eliminated any chance of future AR-10 sales to Cuba, and Castro transferred the ex-Batista AR-10s to a group of Communist revolutionaries from the Dominican Republic.

This final version incorporated all that had been learned to date about the AR-10, including infantry service rifle and field test reports.

In addition to a heavier barrel with chrome-lined chamber, optional bipod, and the removable plastic/metal handguards of the Transitional model, the Portuguese variant had wider bolt lugs, a stronger extractor, a new simplified three-position gas regulator, and a cocking handle featuring a forward bolt assist.

[26] The AR-10 was officially adopted by the Portuguese paratrooper battalions (Caçadores páraquedistas), and the rifle saw considerable combat service in Portugal's counter-insurgency campaigns in Angola and Mozambique.

[35] Portuguese paratroopers found the AR-10 to be not only accurate but reliable in combat, despite rugged service conditions in African jungle and savannah.

[36] A few Portuguese and Sudanese model AR-10s found their way by various means to nearby African countries; in Chad, the AR-10 was much appreciated by members of the French Foreign Legion.

[38] These rifles were used by marksmen accompanying small patrols to eliminate individual enemies at extended ranges in open country.

Paratroopers deploying to Africa in later years were subsequently issued a collapsible stock version of the German Heckler & Koch G3 rifle.

[40] Most of the AR-10 ex-military rifles shipped to the United States were in the form of parts kits, having been previously dismantled, though a few were legally imported as National Firearms Act (NFA) weapons.

Many of these kit rifles were combined with various semi-auto receivers made by civilian manufacturers in order to permit legal ownership.

In 1957, in an effort to increase profits from the ArmaLite venture, Fairchild decided to compete in the U.S. Army's CONARC requirement for a new six-pound, high-velocity, .22-caliber selective-fire rifle accurate to 500 yards.

However, the AR-10 rifle marketed by ArmaLite after 1958 was not the product-improved AR-10 developed by Artillerie Inrichtingen, but rather a design scaled-up from AR-15 plans and specifications, the AR-10A.

[43] In 1959, ArmaLite sold its rights to the AR-10 and AR-15 to Colt Firearms due to financial difficulties, and limitations in terms of manpower and production capacity.

The rifle has a conventional layout; it features an in-line stock, an aluminum alloy receiver and a fiberglass reinforced pistol grip, handguard, and buttstock.

Movement of the bolt carrier was in-line with the bore, greatly improving inherent accuracy, as well as keeping the rifle on target as the gun fired.

All of the belt-fed prototypes experienced numerous issues with feed malfunctions and parts breakages, and these problems were never wholly solved during the weapon's development stage, which ended with the termination of A.I.

Notably, the AR-10B was not designed using the original AR-10 drawings from either ArmaLite or Artillerie Inrichtingen, but instead was based on the AR-15A2, with parts scaled up or redesigned as needed to fire the 7.62×51mm NATO (.308 Winchester) cartridge.