The first design for the IWS2000 was called the Steyr AMR (Anti-Materiel Rifle), but was later changed to the IWS. It fires a 15.2 mm armor piercing fin stabilized discarding sabot round, and is the first man-portable rifle to use this type of ammunition.
This rifle is based on a nine-and-three-quarter inch long recoil mechanism. This is a mechanism usually used on shotguns due to its recoil dampening effect.
Such a system is necessary when firing the heavy 15.2 mm Steyr APFSDS. This design allows for better recoil distribution over a longer period of time. Another interesting function of this weapon is the movement of the barrel itself. When firing the barrel recoils into a shock absorbing hydro-pneumatic sleeve much like those found on a LG 1 Mark II 105 mm Howitzer. The IWS 2000 also uses a remarkable multi-baffle muzzle break to distribute muzzle energy and further reduce recoil, similar to the ones used on D-30 2A18M 122 mm Towed Howitzers. The entire rifle body is made up of a combination of high tension plastics and super light polymers to increase manageability and cut down on weight. The smoothbore barrel is easily detached and packed away for increased mobility.
The projectile is a 15.2 mm APFSDS round which is highly unusual in small arms. This type of round is almost exclusively used in tank or anti-tank rounds. The round was designed specifically for the IWS 2000. It contains either a tungsten carbide or depleted uranium armor piercing penetrator that is capable of penetrating over 40 mm of rolled homogeneous armor at a range of 1000 m, as well as causing considerable damage behind the target with secondary fragmentation. The cartridge is a unique design including a plastic case with a steel head as well as a plastic sabot shell around the penetrator.