The F88 Austeyr, more commonly known by todays society as the Steyr AUG is a weapon system developed as a bullpup, reducing the overall length of the weapon, it is chambered for a 5.56x45mm NATO Round. The system utilises the conventional gas system and also fires from a closed bolt, reducing foreign material entering the working parts of the weapon. 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 F88 is a modular configuration rifle that employs a high level of polymer and advanced alloy components.
The Primary varient of this rifle is the F88 A3, currently used by the Australian Defence Force. This rifle consists of 6 main part groups. These are the Barrel, Receiver, Stock, Bolt, Trigger Mechanism and Magazine.
As stated above, the F88 is chambered for the 5.56x45mm NATO cartridge and has the standard 1:7 rifling twist. This will stabilize both SS109/M855 and M193 bullets. The standard rifle made by Steyr Mannlicher is made with a 1:9 twist.
The rifle features an Spz-kr type 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 Force's variant of the rifle, and soon after, the Australian Defence Force's 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 130 g (4.6 oz). The light support weapon version of the F88 uses an extended 42-round magazine. An Argentine version of the FN FAL chambered in 5.56 mm NATO and known as the FALMP III Type 2 also used the AUG 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 300 m (984.3 ft) a 180 cm (5.9 ft) tall man-size target will completely fill it, giving the shooter an 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 300 m. 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 350 mm (13.8 in), 407 mm (16.0 in) and 508 mm (20.0 in) length barrels, whereas the 621 mm (24.4 in) 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.
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 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.
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 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.
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 aluminium 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. 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. There is a cavity under the buttplate that holds a cleaning kit.