The Steyr AUG () is an Austrian bullpup assault rifle chambered for the 5.56×45mm NATO intermediate cartridge, designed in the 1960s by Steyr-Daimler-Puch, and now manufactured by Steyr Arms GmbH & Co KG. It was adopted by the Austrian Army in 1978 as the StG 77 (Sturmgewehr 77), where it replaced the 7.62×51mm NATO StG 58 automatic rifle (a licence-built FN FAL). In production since 1978, it is the standard small arm of the Bundesheer and various Austrian federal police units, and its variants have also been adopted by the armed forces of dozens of countries, with some using it as a standard-issue service rifle. Steyr AUG importation into the United States began in the 1980s as the AUG/SA (SA denoting semiautomatic). 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 gun barrel left unthreaded to prevent attachment of flash hiders and suppressors. The ban sunsetted in 2004, and in 2008 Steyr Arms worked with Sabre Defence to produce parts legally in the U.S. Design details The Steyr AUG is a selective-fire, bullpup weapon with a conventional gas-piston-operated action that fires from a closed bolt. It is designed as a Modular Weapon System that could be quickly configured as a rifle, a carbine, a sniper rifle, a sub-machine gun and even an open-bolt squad automatic weapon. The AUG employs a very high level of advanced firearms technology and is made with the extensive use of polymers and aluminium components. It is chambered in 5.56×45mm NATO cartridge and has the standard 1:9 rifling twist that will stabilise both SS109/M855 and M193 rounds. Some nations including Australia, Ireland and New Zealand use a version with a 1:7 twist optimised for the SS109 NATO round. The submachine gun variants are chambered in 9×19mm Parabellum. The AUG consists of six interchangeable assemblies: the barrel, receiver with integrated telescopic sight or Picatinny rail, bolt carrier assembly, trigger mechanism, stock and magazine. Operating mechanism 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