SIG 551 chambered for the widely used 5.56 x 45mm NATO caliber using Swiss Polymer magazines. The SIG551-A1 features a distinctive swiss folding stock, and a M1913 rail for accessory attachment. The 16″ barrel features a four-grove rifling and a twist rate of 1:7″.
The SIG551-A1 measures 36.1″ but can fold to 26″, making it ideal for situations where maximum maneuverability is required. For Special Forces requiring an accurate, more potent rifle, chambered in 5.56 x 45mm NATO, the SIG551-A1 sets a new standard for dependable operation and function.
The SG 553 is an improved version of the SG 552 and was released in 2008. Even though it mostly resembles the SG 552, the SG 553 has one key advantage, the recoil spring is now wrapped around the piston rod as in the SG 550/551 models, which address several reliability issues encountered in the SG 552 and also allows the usage of the standard SG 550/551 charging handle.
The SG 553 series rifles have a 339 mm (13.3 in) lon.
In place of the odd blowback action of its previous design, SIG developed a gas-operated system. The heart of this is a rotating bolt and carrier assembly pirated directly from Kalashnikov’s Automate series. Unlike the Russian design, though, the SIG’s gas system is adjustable to allow an operator to compensate for a dirty weapon.
The firearm is fed by lightweight 20-round box magazines, 30-, 10- and 5-round