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). 
7.92×33mm Kurz The 7.92×33mm "Kurz (designated as the 7.92 x 33 kurz by the C.I.P.) is a rimless bottlenecked intermediate rifle cartridge developed in Nazi Germany prior to and during World War II. The ammunition is also referred to as 7.9mm "Kurz ("German: "Kurz" " meaning "short"), 7.9 "Kurz", or 7.9mmK, or 8×33 Polte. It was specifically intended for development of an automatic carbine (assault rifle). The round was developed as a compromise between the longer 7.92×57mm rifle and the 9×19mm Parabellum pistol rounds, and is known as an intermediate cartridge (German: "Mittelpatrone" ).