page_title: Steyr AUG
section_title: Operating mechanism
hierarchical_section_title: Steyr AUG / Design details / Operating mechanism
caption_attribution_description: Deutsch: 30 Schuss .223 Remington für STG77; Magazin zur Selbstverteidigung im AssE GRÜ
context_page_description: The Steyr AUG is an Austrian 5.56×45mm NATO bullpup assault rifle, designed in the 1960s by Steyr-Daimler-Puch and now manufactured by Steyr Mannlicher GmbH & Co KG.
  It was adopted by the Austrian Army as the StG 77 in 1978, where it replaced the 7.62×51mm NATO StG 58 automatic rifle. In production since 1978, it is the standard small arm of the Austrian Bundesheer and various national police units. Its variants have also been adopted by the armed forces of dozens of countries.
  Steyr AUG importation into the U.S. began in the 1980s as the AUG/SA. President George H.W. Bush banned the AUG via an executive order under the 1989 Assault Weapon Import ban. Six years into the ban, AUG buyers gained a reprieve as cosmetic changes to the carbine’s design allowed importation once again. Changes included the pistol grip being changed into a thumbhole stock, and the barrel left unthreaded to prevent attachment of flash suppressors and silencers. The ban sunsetted in 2004, and in 2008 Steyr Arms worked with Sabre Defense to produce parts legally in the U.S.
context_section_description: The AUG has a rotating bolt that features 7 radial locking lugs and is unlocked by means of a pin on the bolt body and a recessed camming guide machined into the bolt carrier. The bolt carrier itself is guided by two guide rods brazed to it and these rods run inside steel bearings in the receiver. The guide rods are hollow and contain the return springs. The bolt also contains a claw extractor that forms the eighth locking lug and a spring-loaded "bump"-type casing ejector.
  The gas cylinder is offset to the right side of the barrel and works with one of the two guide rods. The AUG uses a short-stroke piston system where the right guide rod serves as the action rod, transmitting the rearward motion of the gas-driven piston to the bolt carrier. The left-hand rod provides retracting handle pressure when connected by the forward assist and can also be utilised as a reamer to remove fouling in the gas cylinder. The firearm uses a 3-position gas valve. The first setting, marked with a small dot, is used for normal operation. The second setting, illustrated with a large dot, indicates fouled conditions. The third, "GR" closed position is used to launch rifle grenades (of the non-bullet trap type).
  The AUG is hammer-fired and the firing mechanism is contained in the rear of the stock, near the butt, covered by a synthetic rubber shoulder plate. The hammer group is made entirely of plastics except for the springs and pins and is contained in an open-topped plastic box which lies between the magazine and the buttplate. During firing the recoiling bolt group travels over the top of it, resetting the hammer. Since the trigger is located some distance away, it transmits its energy through a sear lever which passes by the side of the magazine. The firing pin is operated by a plastic hammer under pressure from a coil spring.
caption: Steyr AUG with a loaded 30-round magazine.
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