The SIG SG 552 Commando is variant of the swiss assault rifle SIG SG 550. 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-ownedWaffenfabrik Bern, using both 6.45×48mm and 5.6×45mm cartridges) and the SG 541 (developed by SIG). In 1981, the experimental6.45mm 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.
In February 1983, the decision to adopt the SG 541 was publicly announced (the designation of the rifle was changed in October of the following year to SG 550, while the carbine version became known as the SG 551). The rifle was officially accepted into service in 1990, hence the military designation Stgw 90. Over 600,000 rifles have been delivered since then and production for the military has now ceased.
The compact SG 552 Commando (full designation as the 552-2P) carbine was released in 1998. It has a shorter 226 mm (8.9 in) barrel (with an open, 3-prong flash suppressor) and gas tube, ventilated handguards and a redesigned bolt carrier group that was integrated with the piston rod to form a single moving assembly. The SG 552 series rifles have a 360 mm (14.2 in) long sight radius. The return mechanism has been moved to the rear of the receiver housing and its recoil spring is guided in a way analogous to that of the AK-47: on a steel guide rod (later models feature a polymer guide rod) resting against the lower receiver’s rear surface under tension of the compressed recoil spring. Like the SG 550/551, this model can accept rails and accessories enabling the use of optics. A long barrel version of the SG 552 known as the SG 552 LB incorporates a 346 mm (13.6 in) barrel with provision to fire rifle grenades and support a bayonet.