Which riffle on which SIG SG 550 is based is a 5.56×45mm NATO assault rifle developed in the early 1970s by Schweizerische Industrie Gesellschaft?
SIG SG 550 The SG 550 is an assault rifle manufactured by Swiss Arms AG (formerly a division of Schweizerische Industrie Gesellschaft now known as Sig Holding AG) of Neuhausen, Switzerland. "SG" is an abbreviation for "Sturmgewehr", or "assault rifle". The rifle is based on the earlier 5.56mm SG 540 and is also known as the Fass 90 ("Fusil d'assaut" 90/"Fucile d'assalto" 90) in French/Italian or Stgw 90 in German ("Sturmgewehr" 90). 
Assault gun An assault gun is a form of self-propelled artillery which utilizes an infantry support gun mounted on a motorized chassis, normally an armored fighting vehicle. Assault guns are designed to provide direct fire support for infantry attacks, especially against other infantry or fortified positions. The term is a literal translation of the German word "Sturmgeschütz", which was applied to the first purpose-built assault gun, the StuG III, in 1940.