Right side view of a SIG SG-550 full length assault rifle.
Source: Stw - © GNU Attribution - Share Alike license
The SG-550 is a modern assault rifle of Swiss origin. It was developed to replace the elderly Sturmgewehr 57 in Swiss service. The design is based on the SG-540, which was developed by SIG for export sales. The SG-550 is renowned for its high production quality and good performance.
The SG-550 was derived from the SG-541, which was a higher quality proof of principle based on the earlier SG-540. The SG-550 is gas operated and uses a long stroke gas piston. The receiver, barrel and internal mechanism are made out of metal and the forearm, magazines and the side folding stock out of plastics. Diopter sights are fitted and optics are easily installed.
The SG-550 fires the 5.6x45mm GP90 round, which is a Swiss derivative of the 5.56x45mm round. For export sales the SG-550 is available in the 5.56x45mm NATO round with associated faster twist rate. Translucent 20 and 30 round magazines are used. The firing selector allows for single shot, three round burst and full automatic fire at 700 rpm. Effective range is about 400 meters.
The main user of the SG-550 is the Swiss military with over 600.000 rifles adopted. No other nation adopted it as its standard assault rifle. It has been widely adopted by a wide variety of special military and law enforcement units. Due to its production quality and limited age the SG-550 remains in active use.
The SG-550 is the standard full size rifle from which all other versions have been derived. For use as a designated marksman rifle it can be fitted with optics, such as the 4x24mm Kern optics used by the Swiss army. The SG-550 can be fitted with the GL 5040 under barrel grenade launcher and is also capable of launching rifle grenades.
The SG-551 is the carbine model of the SG-550. Its design is identical to the SG-550, but it features a shorter barrel and forearm. The latest addition is the SG-551 LB which features a longer barrel than the original SG-551, which allows it to mount bayonets and fire rifle grenades. The SG-551 can be fitted with the GL 5140 under barrel grenade launcher.
The SG-551-1P and SG-551 SWAT are preconfigured rifles for law enforcement use. Both models include optics and a cheekpiece on the stock. The SG-551-1P features the Hensoldt 6x42 BL scope. The SWAT model is more commonly found with an ACOG 4x scope on a proprietary mount, a bipod and accessory rails for laser and light. These preconfigured models are now discontinued since Picatinny rails have become optional.
The SG-552 Commando is the most compact variant of the SG-550. This weapon and its variants are described in a separate article.
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