The SIG SG 550 series is the culmination of a long line of Swiss rifle development. The progenitor is the Swiss Army’s previous service rifle, the SIG SG 510. Also known as the Sturmgewhr 57, the 510 used a roller-delayed blowback action and fired the 7.5x55mm round (a 7.62x51mm version was produced by Beretta for export).
With the rise of the 5.56mm cartridge during the 1960s, SIG began work on a rifle to fire it. At this point there was no Swiss military requirement for a new rifle, it was being developed with foreign sales in mind. Continuing their partnership with Beretta, SIG developed the SG 530 (Beretta eventually went their own way, going on to develop the AR70 rifle). Rather unusually, the 530 combined roller-delayed blowback with a gas piston in a hybrid operating system. This arrangement never proved satisfactory and the SG 530 did not enter production.
For their next attempt, SIG discarded the roller delayed blowback system and looked to the Kalashnikov for the basis of their gas system and bolt design. With some Swiss refinements this proved to be just the ticket and it entered production as the SG 540.
Again, the rifle was intended for foreign sales. Due to Swiss export law production was carried out at the MANUHRIN factory in France, and eventually licensed to Portugal (INDEP) and Chile (FAMAE). The SG 540 was adopted by over 20 countries. It was even the standard service rifle of the French Army during the 1970s while the FAMAS was under development.
In 1978 the Swiss Army formulated a requirement to replace the SIG 510. SIG submitted the SG 541, a modified version of the 540. It won the competition over the Waffenfabrik Bern C42 and was chosen as the Swiss Army’s new service rifle in 1983. Interestingly, that the new rifle would be chambered in 5.56mm was not a foregone conclusion. Prototypes were tested in 6.5x48mm GP80. Eventually the Swiss chose to adopt the 5.6mm Gw Pat 90 (GP90). Despite the 5.6mm designation, this is actually a 5.56x45mm cartridge and is interchangeable with standard NATO or .223 ammunition.
Financial considerations delayed production for several years. The new rifle, now designated the SG 550 by SIG and the Sturmgewher 90 by the Swiss military, entered service in 1990. It spawned an impressive family of variants.
From top to bottom: The SIG SG 550, SG 551 LB, SG 551, and SG 552 Commando