SIG-556
Summary
| Country | 🇺🇸 United States |
| Category | Assault rifle |
| Manufacturer | Sig Sauer |
Technical specifications
| SIG-556 | |
|---|---|
| Fire Rate | 800 rounds/min. |
| Caliber | 5.56 x 45 mm OTAN |
| Magazine | 30 rounds |
| Length | 940 mm (37.0 in) |
| Weight | 3.54 kg (7.8 lb) |
| Range | 450 m (1476 ft) |
Description
Development of a successor to the Stgw 57 battle rifle began in Switzerland in 1978, with emphasis on modularity, reduced weight, and maintained accuracy. This led to a competition between the W+F C42 and the SIG SG 541. In 1981, the experimental 6.45mm cartridge was replaced by a 5.6x45mm round equivalent to the 5.56x45mm NATO. The SG 541 was selected in February 1983 and later designated the SG 550 in October 1984. Production commenced in 1986, and the rifle was officially adopted as the Stgw 90 in 1990. Over 600,000 rifles have been delivered, and production for military use has ceased.
The SG 550 is a selective-fire 5.56x45mm NATO rifle that operates from a closed bolt. It utilizes a gas-actuated, piston-driven, long-stroke system derived from the SIG SG 540, featuring a manually adjustable gas valve. Locking is achieved via a rotary bolt with two steel lugs. The firearm is hammer-fired and includes an ambidextrous safety and fire selector offering "S" (safe), "1" (single), "3" (3-round burst), and "20" (full automatic) settings, with options to disable burst and automatic modes. It feeds from translucent polymer magazines of various capacities that can be linked together and includes a bolt hold-open device. The rifle features a side-folding skeletonized buttstock and an aluminum bipod. Barrels are heavy and cold hammer-forged, equipped with a slotted flash suppressor that allows for rifle grenade launching and bayonet attachment.
Accuracy testing is conducted at 300m, with production rifles tested for R50 dispersion. Standard iron sights include a rear rotating diopter and hooded front post, adjustable for windage and elevation with specific range settings up to 400m, including night use tritium inserts. Optics can be mounted via quick-detachable rails or an integral Picatinny rail version. Standard accessories include a spare magazine, sling, cleaning kit, and loading aid. It can be fitted with GL 5040/5140 or GL 5340 underbarrel grenade launchers and an Stgw 90 bayonet or certain NATO-pattern bayonets with an adapter.
Variants include: * The SG 551 carbine, which features a shorter barrel and different handguards, lacking the bipod, bayonet lug, and rifle grenade capability in its base form (although an SG 551 LB version incorporates an extended barrel for these features).
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Specialized SG 551 versions, such as the 551-1P police carbine and 551 SWAT.
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The compact SG 552 Commando, which has an even shorter barrel and redesigned bolt carrier group with a rear-mounted recoil spring, superseded by the SG 553 in 2008.
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The SG 553, which improves reliability by returning the recoil spring to its position around the piston rod.
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The SG 552 and 553 LB versions, which accommodate bayonet and rifle grenade use.
The SG 553 series includes variants chambered in 7.62x39mm (SG 553 R) and .300 AAC Blackout (SG 553 BK). An upgrade kit is available to convert the SG 552 to the SG 553 configuration, designated SG 552-A1. The SG 550-1 Sniper, designed for police, is accurized with a heavier barrel, refined trigger, and adjustable stock and grip. Civilian semi-automatic versions, such as the SP, PE 90, and SIG Sport, are available with either 178mm or 254mm twist rate barrels. The SIG 556 series was produced in the United States for the civilian market and accepted M16 magazines and M4 stocks; it includes variants such as the Classic, DMR, P556 pistol, R (7.62x39mm), and xi models. Production of the SIG 556 was discontinued as of 2017. The SIG 522LR is a separate .22-caliber sporting rifle styled after the series but featuring a simple blowback action.
The firearm was adopted by the Swiss Armed Forces. The SG 550-1 Sniper variant was designed at the request of the Swiss Police.