page_title: ArmaLite AR-10
section_title: Design details
hierarchical_section_title: ArmaLite AR-10 / Design details
caption_attribution_description: Français&#160;: photo AR10
context_page_description: The ArmaLite AR-10 is a 7.62×51mm NATO battle rifle developed by Eugene Stoner in the late 1950s and manufactured by ArmaLite, then a division of the Fairchild Aircraft Corporation. When first introduced in 1956, the AR-10 used an innovative straight-line barrel/stock design with phenolic composite and forged alloy parts resulting in a small arm significantly easier to control in automatic fire and over 1 lb lighter than other infantry rifles of the day. Over its production life, the original AR-10 was built in relatively small numbers, with fewer than 10,000 rifles assembled. However, the ArmaLite AR-10 would become the progenitor for a wide range of firearms.
  In 1957, the basic AR-10 design was rescaled and substantially modified by ArmaLite to accommodate the .223 Remington cartridge, and given the designation ArmaLite AR-15.
  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. After modifications, the new redesigned rifle was subsequently adopted by the U.S. military as the M16 Rifle.
context_section_description: The AR-10 is a lightweight, air-cooled, magazine-fed, gas-operated rifle that uses a piston within the bolt carrier with a rotary bolt locking mechanism. 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. While mostly an original design, the AR-10 built upon previously proven concepts. From the FAL it took the hinged receiver system allowing the rifle to be opened for cleaning much like a break-action shotgun. The ejection port cover is similar to that found on the German World War II-era StG44. The bolt locking mechanism is similar to the M1941 Johnson rifle (itself an adaptation of the Browning-designed Remington Model 8 bolt). From the German MG 13 light machine gun, FG 42 and M1941 Johnson machine gun came the idea of the straight-line stock layout. A "straight-line" recoil configuration increases controllability during burst or automatic fire by reducing muzzle climb. The AR-10's method of rotary bolt locking, straight-line recoil, and gas operation enhanced its inherent accuracy.
  The original AR-10 action (later developed into the ArmaLite AR-15 and M16 rifle) designed by Eugene Stoner is commonly called a direct impingement system, but it does not utilize a conventional direct impingement system. In U.S. Patent 2,951,424, the designer states: ″This invention is a true expanding gas system instead of the conventional impinging gas system.″ 
  The gas system, bolt carrier, and bolt-locking design were novel for the time. Most gas-operated rifles divert combustion gases from a port in the barrel to a piston and cylinder arrangement adjacent to the port. In Stoner's design, the gas travels from a port near the middle of the barrel through a steel tube back into the receiver. The gas enters a chamber inside the bolt carrier formed between the rear of the bolt and the inside of the bolt carrier. The bolt within the bolt carrier is fitted with piston rings to contain the gas. Once the bolt carrier moves to the rear a small distance, excess gas is vented through holes in its side. This use of the bolt and bolt carrier for the separate actions of a piston and gas cylinder simplified construction and saved weight. 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. Since the straight-line stock placed the shooter's eye well above the barrel the rifle's sights were mounted high, with the rear sight contained in a carrying handle that also protected the cocking/charging lever.
  The receiver is made from forged and machined aluminum to reduce weight. The bolt locks into an extension on the barrel instead of the receiver allowing for a lightweight receiver while not compromising the strength of the bolt locking mechanism. On a few prototype guns, an all-aluminum ("Sullaloy") barrel was fitted at the insistence of George Sullivan – ArmaLite's president – though after the 1957 Springfield Armory tests, all production AR-10s were fitted with standard steel barrels.  The stock is made from a fiberglass-reinforced phenolic composite with a core of rigid plastic foam. The handguards and pistol grip are also fiberglass reinforced plastic. Fairchild was an aircraft manufacturer, and the use of plastics, titanium, and aluminum were common in the aircraft industry at the time, though not generally used in firearms.
  Several experimental prototypes of a belt-fed variant of the AR-10 were developed by ArmaLite and A.I. engineers, informally designated the AR-10 LMG. In one version, the belt was fed by a feed-chute connected to a 250-round ammo box carried on the user's back. 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.'s production contract. As a result, no AR-10 LMG variants were ever sold.
caption: AR-10 bolt
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