SIG SG 550

SG 550
The SG 550 service rifle
Type	Assault rifle
Place of origin	Switzerland
Service history
In service	1990–present
Used by	See Users
Production history
Designer	Schweizerische Industrie Gesellschaft
Designed	1970s–1980s
Manufacturer	Swiss Arms AG (formerly Schweizerische Industrie Gesellschaft)
Produced	1986–present
No. built	600,000+
Variants	See Variants
Specifications
Weight	SG 550: 4.1 kg (9.04 lb) SG 551: 3.40 kg (7.5 lb) SG 552 Commando: 3.2 kg (7.1 lb) SG 553: 3.2 kg (7.1 lb) SG 550 Sniper: 7.02 kg (15.5 lb)
Length	SG 550 (stock extended): 998 mm (39.3 in) SG 550 (stock folded): 772 mm (30.4 in) SG 551 (stock extended): 833 mm (32.8 in) SG 551 (stock folded): 607 mm (23.9 in) SG 552 Commando (stock extended): 730 mm (28.7 in) SG 552 Commando (stock folded): 504 mm (19.8 in) SG 553 (stock extended): 730 mm (28.7 in) SG 553 (stock folded): 501 mm (19.7 in) SG 550 Sniper (stock extended): 1,130 mm (44.5 in) SG 550 Sniper (stock folded): 905 mm (35.6 in)
Barrel length	SG 550: 528 mm (20.8 in) SG 551: 363 mm (14.3 in) SG 552 Commando: 226 mm (8.9 in) SG 553: 227 mm (8.9 in) SG 550 Sniper: 650 mm (25.6 in)
Cartridge	5.56×45mm NATO (5.6mm Gw Pat 90)
Action	Gas operated, rotating bolt
Rate of fire	Approx. 700 rounds/min
Muzzle velocity	SG 550: 911 m/s (2,989 ft/s) SG 551: 850 m/s (2,788.7 ft/s) SG 552 Commando: 725 m/s (2,378.6 ft/s) SG 550 Sniper: 940 m/s (3,084.0 ft/s)
Effective firing range	100–400 m sight adjustments
Feed system	5-, 20-, or 30-round detachable box magazine
Sights	Rear: rotating diopter drum with tritium night inserts; front: hooded post with folding night post 540 mm (21.3 in) sight radius (SG 550) 466 mm (18.3 in) sight radius (SG 551)

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).

In 1978, the Swiss Army formulated requirements for a successor to the Stgw 57 battle rifle (known commercially as the SG 510) using the 7.5×55mm Schmidt–Rubin 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 6.45×48mm and 5.6×45mm 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 5.6×45mm GP 90 round (with a 4.1 g, tombac-jacketed, lead core projectile) that is the Swiss equivalent to NATO's standard 5.56×45mm cartridge.