The AUG is an Austrian bullpup 5.56mm assault rifle was adopted by the Austrian Army as the StG 77 (Sturmgewehr 77) in 1977, where it replaced the 7.62mm StG 58 automatic rifle. In production since 1978, it is the standard small arm of the Austrian Bundesheer and various national police units.
The rifle has also been adopted by the armed forces of Argentina, Australia (accepted into service in 1985 and manufactured by Australian Defence Industries in Lithgow, this Austeyr model is also in use by New Zealand), Bolivia, Ecuador (since 1988), Republic of Ireland, Luxembourg, Saudi Arabia, Tunisia (introduced in 1978), Pakistan, and (since 1988) U.S. Customs (now the U.S. Immigration and Customs Enforcement agency).
The AUG, a bullpup 5.56mm assault rifle, is a selective fire weapon with a conventional gas piston operated action that fires from a closed bolt. Designed as a family of rifles that could be quickly adapted to a wide variety of roles with the change of the barrel to a desired length and profile, the AUG is a modular configuration rifle that employs a high level of polymer and advanced alloy components.
The primary variant of the rifle, designated the AUG A1, consists of six main assemblies: the barrel, receiver with integrated telescopic sight, bolt and carrier, trigger mechanism, stock and magazine.
The AUG uses the 5.56x45mm NATO cartridge and the standard 1:9 rifling twist will stabilize both SS109/M855 and M193 bullets. Some nations including Australia and New Zealand use a version with a 1:7 twist optimised for the SS109 NATO round.
The Steyr AUG rifle is fully ambidextrous. It can be configured for use by left-handed shooters by simply changing the bolt for a left-handed one with the extractor and ejector on opposite sides, and moving a blanking cap from the left ejection opening to the right.
Variants include a compact 350 mm (13.8 in) barrel, 407 mm (16.0 in) carbine barrel, 508 mm (20.0 in) standard rifle-length barrel and a 621 mm (24.4 in) light machine gun barrel.
Rifles equipped with 407 mm (16.0 in) and 508 mm (20.0 in) barrels are able to launch rifle grenades. 508 mm (20.0 in) pattern barrels produced for military purposes are also equipped with a bayonet lug. The manufacturer offers two other 508 mm (20.0 in) barrel configurations: the first – fitted with a fixed, post foresight (used on the standard rifle version with aperture iron sights) and the second type – equipped with a 40 mm M203 grenade launcher that can be used mounted on the standard length rifle or autonomously – as a stand-alone grenade launcher after attaching a shoulder pad to the end of the 5.56 mm barrel.