High Quality Content by WIKIPEDIA articles! The SG 540 is a 5.56mm assault rifle developed in the early 1970s by Schweizerische Industrie Gesellschaft (SIG, currently SAN Swiss Arms AG) based out of Neuhausen, Switzerland as a private venture primarily destined for export markets and as a potential replacement for the 7.5mm SG 510 automatic rifle known as the Stgw 57 in Swiss service.