 The StG 58 was replaced by the Steyr AUG (designated StG 77) in 1977, although the StG 58 served with many units as the primary service rifle through the mid-1980s.A semi-automatic, twin-barrel variant chambered in the 5.56mm "Duplex" round during Project SALVO.This weapon was designed by Stefan Kenneth Janson who previously designed the EM-2 rifle.