The Sturmgewehr 57 (Stgw. 57 ) is a selective fire battle rifle designed by Schweizerische Industrie Gesellschaft (now SAN Swiss Arms) of Switzerland. The Stgw. 57 assault rifle uses a roller-delayed blowback system similar to the blowback system of the Heckler & Koch G3 (H&K G3) and CETME rifles. As an assault rifle, the model AM 55 entered service in the Swiss Army in three designations F. ass. 57 7.5mm (Fr: Fusil d’Assaut; Ital: Fucile d’Assalto 1957) and 7.5mm Stgw. 57 (Ger: Sturmgewehr 1957). Technologically, the Stgw. 57 was the mechanical and design basis for the export-variations of the SG 510 family of small arms. After thirty-three years, from 1957 to 1990, the Swiss Army replaced the Stgw. 57 with the SIG SG 550, a lighter-weight assault rifle.