The ISL 274 40 mm grenade launcher was developed by ISTEC to meet an Australian Army requirement for an under slung 40 mm grenade launcher to fit onto the Steyr AUG/F88 5.56 mm assault rifle. It is a manually fired, fixed breech, side-opening weapon that can be under slung from an AUG barrel by means of interface brackets. A cutaway lower hand guard replaces the standard item and can be used when the grenade launcher is not attached to the rifle. The main components of the grenade launcher are manufactured from hard-anodized aluminum alloy. Other components are stainless steel. The firing mechanism is of the double-action type. As the launcher breech is opened, the spent case is ejected automatically. The direction of opening of the side-opening barrel can be to either side to meet individual user requirements; the conversion can be carried out by the user in the field. Barrel locking levers are on both sides of the grenade launcher body.
A sight unit is attached to the grenade launcher body, graduated in 50 m increments from 50 to 300 m. The sight can be secured to either the left or right-hand side of the launcher. When not in use, the grenade launcher is carried in a webbing carrying case.
Calibre: 40 mm
Operation: single shot
Weight: grenade launcher and sight, 1.2 kg; interface bracket, 180 g
Length: grenade launcher, 280 mm
Sights: 50 to 300 m in 50 m steps
Trigger pull force: 1st pull, 40 N; release pull, 70 N
Muzzle velocity: 76 m/s