The Steyr AUG was designed in the early '70s by the Austrian defense firm Steyr Mannlicher GmbH for the Austrian Army. Since then, it has spread to many users worldwide who enjoy its low weight and compact arrangement. Since its inception it has evolved into variants tailored for many missions and situations, including a submachine gun variant firing pistol ammunition. (AUG Para) The strict gun laws of the United States ban most versions, however there are some produced under license in the US and specifically tailored for domestic legality. Within the Bundesheer (Austrian Armed Forces) it is commonly called "StG77", StG standing for "Sturmgewehr" (assault rifle).
The AUG has many desirable features. It fires fairly common 5.56x45mm NATO ammunition in rifle form and the ubiquitous 9mm as an SMG. The heavy use of polymer components keeps the weight down, even the magazines are polymer. The bullpup arrangement is more compact in overall length compared to more traditional assault rifles. The barrel is of the quick-change variety, allowing the rifle to be fired for long periods as well as making reconfiguration to a different barrel length nearly instantaneous. The gas-piston rotating-bolt firing mechanism is proven and reliable. And the original configuration features an integral 1.5x scope for an effective range of 300m (980ft).
Recent updates to the AUG have resulted in the A3. This new "core" version replaced the integral scope with a rail mounting system allowing the user to mount a variety of scope, sights, and accessories. Support for a grenade launcher is now better integrated as well, and other minor upgrades keep the rifle competitive with more recent designs.