SIG SG 550 (Sturmgewehr Model 550) / Stgw 90 Assault Rifle / Assault Carbine
The SIG SG 550 series has seen widespread use by special forces, regular army and security elements worldwide in its various forms.
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The SIG SG 550 (Sturmgewehr Model 550) series was born in a Swiss Army initiative requiring an automatic weapon chambered for the 5.56x45mm NATO cartridge as a replacement for its 1950s-era SIG SG 510 Battle Rifle. Development of the new system began in 1979 and spanned into 1980. After formal evaluations of two competing systems - the W+F C42 from Swiss Federal Arms Factory and the SIG SG 541 - the SIG submission was selected as the winner. Both designs were initially tested with the 6.45mm GP 80 cartridge and the 5.6x45mm GP 90 cartridge (the latter essentially the Swiss version of the 5.56x45mm NATO cartridge) with the 5.6x45 winning out. The SG 541 was adopted as the next standard Swiss Army self-loading weapon system in 1983 (becoming the SG 550 in 1984) and known formally in the Swiss Army inventory as the "Sturmgewehr 90 (Stgw 90)".
The SG 550 was developed into a family of automatic weapons, each born from the basic automatic action and intended to be inherently modular to produce specialized carbine, commando and sniper rifle forms. This benefitted prospective buyers by way of its logistically friendly design that could arm frontline, secondline and specialized forces units as needed - all sharing the same internal components, ammunition and function/training.