SG 550

The SG 550 is an assault rifle manufactured by Swiss Arms AG (formerly Schweizerische Industrie Gesellschaft) 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
In 1978, the Swiss Army formulated requirements for a successor to the Stgw 57 battle rifle (known commercially as the SG 510) using the 7.5x55mm GP11 cartridge. Emphasis was placed on modularity; the weapon family was to include several variants of the base design, including a compact carbine that would be issued to rear-echelon and support troops, commanding staff, vehicle crews, special operations personnel and paratroopers. Another aim was to reduce the overall weight of the rifle while retaining comparable or improved accuracy out to 300 m. The solicitation was narrowed down to two designs: the W+F C42 (developed by the state-owned Waffenfabrik Bern, using both 6.45x48mm and 5.6x45mm cartridges) and the SG 541 (developed by SIG). In 1981, the experimental 6.45mm GP 80 cartridge was rejected in favor of the more conventional 5.6x45mm GP 90 round (with a 4.1 g, steel-jacketed, lead core projectile) that is the Swiss equivalent to NATO's standard 5.56x45mm cartridge.