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. Semi-automatic only AR-10 production ArmaLite AR-10B series In 1995, former Army Ordnance officer Mark Westrom, owner of Eagle Arms, purchased the ArmaLite brand and the company became ArmaLite Inc. Shortly thereafter, ArmaLite Inc. introduced the completely new semi-automatic-only AR-10B rifle series. 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. The AR-10B prototype was composed of individual sub-components tested on a special lower receiver made of two slabs of aluminum fitted to a Knight's Armament Company SR-25 upper receiver assembly, and prototyped using computer analysis. The full prototype AR-10B was the first rifle off the production line. Since 1995, the new ArmaLite company has also incorporated various other design and engineering improvements to the AR-10, including a newly designed steel magazine derived from the model used on the U.S. M14 rifle. The current ArmaLite AR-10 is offered in several versions including an A2 and A4 rifle or carbine with a collapsible stock, a target model (AR-10T), a "retro" AR-10B with Sudanese AR-10-style handguard and cocking lever (limited production) and one version chambered in 300 Remington SAUM. Current users