This is an excellent example of a rare Armalite prototype rifle, chambered in the .338 Federal cartridge. This round was developed by Federal in 2006, which featured a necked-up .308 case with a .338 bullet. The round was designed to give the better ballistics of the .338 bullet in the shorter case so that it could be used in standard semi-automatic rifles. Has a flat top upper receiver, round grooved forearm, stainless barrel and a stainless railed gas block. The stock is plastic with a rubber stick on cheek rest and has a Hogue rubber pistol grip. The lower receiver is marked "RIFLE 7.62MM" while the upper receiver is marked ".338 FEDERAL". The accompanying letter from Armalite states that the rifle was manufactured in 2007 as a proto-type AR-10 .338 Federal rifle. It further states that the features include a 22" 1-10 twist stainless steel barrel, free float aluminum hand guard, .338 engraved flat top picatinny upper receiver, national match 2 stage trigger, .308 Magnum stamped lower receiver and black furniture. Comes with case.