Steyr AUG The AUG is an Austrian bullpup 5 . 56mm assault rifle , designed in the early 1970s by Steyr Mannlicher GmbH & Co KG ( formerly Steyr - Daimler - Puch ) . The AUG ( " Armee Universal Gewehr " — " universal army 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 ( a license - built FN FAL ) . 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 ) . Design details . 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 . Features . The rifle features a two - stage trigger ( pulling the trigger halfway produces semi - automatic fire , pulling the trigger all the way to the rear produces fully automatic fire ) and a safety mechanism ( cross - bolt , button type ) , located immediately above the hand grip . In its “ safe ” position ( white dot ) the trigger is mechanically disabled ; pressing the safety button to the left exposes a red dot and indicates the weapon is ready to fire . Some versions have an ALO or " automatic lockout " , a small projection at the base of the trigger . This was first included on the Irish Defence Forces variant of the rifle , and soon after , the Australian Defence Forces variant . In the exposed position the ALO stops the trigger being squeezed past the semi - automatic position . If needed , the ALO can be pushed up to permit automatic fire . The rifle is fed from translucent , double - column box magazines ( molded from a high - strength polymer ) with a 30 - round capacity and an empty weight of . The light machine gun version of the AUG uses an extended 42 - round magazine . Integrated with the receiver casting is a fixed carry handle that contains a 1 . 5x telescopic sight made by Swarovski Optik . It contains a simple black ring reticle with a basic rangefinder that is designed so that at a tall man - size target will completely fill ( subtend ) it , giving the shooter a relatively accurate method of estimating range . The sight cannot be set to a specific range but can be adjusted for windage and elevation for an initial zero and is designed to be calibrated for 300 m . When so set , aiming at the centre of a target will produce a hit at all ranges out to 300m . The rifle also has a back - up iron sight with a rear notch and front blade , cast into the top of the aluminum optical sight housing , used in case of failure or damage to the primary optical sight . The sight is also equipped with a set of three illuminated dots ( one on the front blade and two at the rear ) for use in low - level lighting conditions . In order to mount a wide range of optics and accessories , a receiver with a NATO - standard Picatinny rail and detachable carry handle was also developed and introduced in 1997 . Three - pronged , open - type flash suppressors were used on the , and length barrels , whereas the light machine gun barrel received a closed - type ported muzzle device ( combination flash suppressor and compensator ) and an integral , lightweight folding bipod . The flash suppressors are screwed to the muzzle and internally threaded to take a blank - firing attachment . The rifle comes standard with four magazines , a muzzle cap , spare bolt for left - handed shooters , blank - firing adaptor , cleaning kit , sling and either an American M7 or German KCB - 77 M1 bayonet . Modularity . The 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 barrel , carbine barrel , standard rifle - length barrel and a light machine gun barrel . Rifles equipped with and barrels are able to launch rifle grenades . pattern barrels produced for military purposes are also equipped with a bayonet lug . The manufacturer offers two other barrel configurations : the first – fitted with a fixed , post foresight ( used on the standard rifle version with aperture iron sight s ) 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 . Operating mechanism . The rotating bolt 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 used to remove fouling in the gas cylinder by utilizing the left - hand guide rod as a reamer . 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 grenade s ( 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 . Engineering . The quick - change barrel used in the AUG is cold hammer - forged by GFM - GmbH of Steyr Austria for increased precision and durability , its bore , chamber and certain components of the gas system are chrome - plated . The standard rifle - length barrel features 6 right - hand grooves and a rifling twist rate of 228 mm ( 1 : 9 in ) . An external sleeve is shrunk on to the barrel and carries the gas port and cylinder , gas valve and forward grip hinge jaw . There is a short cylinder which contains a piston and its associated return spring . The barrel locks into a steel insert inside the receiver through a system of eight lugs arranged around the chamber end and is equipped with a folding , vertical grip that helps to pivot and withdraw the barrel during barrel changes . The most compact of the barrels has a fixed vertical grip . The receiver housing is a steel - reinforced aluminum extrusion finished with a baked enamel coating . It holds the steel bearings for the barrel lugs and the guide rods . The non - reciprocating plastic cocking handle works in a slot on the left side of the receiver and is connected with the bolt carrier ' s left guide rod . The cocking handle has a forward assist feature – alternatively called a " silent cocking device " – used for pushing the bolt shut without recocking the rifle . A bolt hold - open device locks the bolt carrier assembly back after the last round has been fired . The AUG lacks a bolt release button , and the cocking handle must be retracted to release the bolt group after a new magazine has been inserted . The rifle ’ s stock is made from fiberglass - reinforced polyamide 66 . At the forward end is the pistol grip with an enlarged forward trigger guard completely enclosing the firing hand that allows the rifle to be operated with winter gloves . The trigger is hung permanently on the pistol grip , together with its two operating rods which run in guides past the magazine housing . Behind that is the locking catch for the stock group . Pressing this to the right will separate the receiver and stock . The magazine catch is behind the housing , on the underside of the stock . Above the housing are the two ejector openings , one of which is always covered by a removable strip of plastic . The rear of the stock forms the actual shoulder rest which contains the hammer unit and the end of the bolt path . The butt is closed by an endplate which is held in place by the rear sling swivel . This swivel is attached to a pin which pushes in across the butt and secures the plate . Variants . A semi - automatic version of the rifle known as the AUG P is available to the civilian and law enforcement markets . It features a shorter , barrel and a modified bolt , carrier and trigger assembly that will only allow semi - automatic fire . The rifle also has a slightly different optical sight that features a reticule with a fine dot in the center of the aiming circle , allowing for more precise aiming . The light machine gun variant can be modified to fire from an open bolt ( called the AUG LMG in this configuration ) . To accomplish this , a modified bolt carrier , striker and trigger mechanism with sear are used . Based on the AUG , Steyr developed the 9 mm AUG submachine gun that fires the 9x19mm Parabellum pistol cartridge . It is an automatic , blowback - operated model that fires from a closed bolt . Unlike the rifle variants , this SMG has a unique barrel with 6 right - hand grooves at a 250 mm ( 1 : 9 . 8 in ) rifling twist rate , ended with a recoil compensator , a slightly different charging handle and a magazine well conversion insert enabling the use of standard 25 - round box magazines from the Steyr MPi 81 and TMP submachine guns . A conversion kit used to transform any rifle variant into the submachine gun is also available . It consists of a barrel , bolt , adapter insert and magazine .