SIG SG 550

SIG SG 550
SG 550
Stgw 90.jpg
The SG 550 service rifle
Type Assault rifle
Place of origin  Switzerland
Service history
In service 1990–present
Used by See Users
Production history
Designer SIG
Designed 1970s
Manufacturer Swiss Arms AG (formerly SIG)
Produced 1986–present
Number built 600,000+
Variants See Variants
Weight SG 550: 4.1 kg (9.04 lb)
SG 551: 3.40 kg (7.5 lb)
SG 552 Commando: 3.2 kg (7.1 lb)
SG 553: 3.2 kg (7.1 lb)
SG 550 Sniper: 7.02 kg (15.5 lb)
Length SG 550 (stock extended): 998 mm (39.3 in)
SG 550 (stock folded): 772 mm (30.4 in)
SG 551 (stock extended): 833 mm (32.8 in)
SG 551 (stock folded): 607 mm (23.9 in)
SG 552 Commando (stock extended): 730 mm (28.7 in)
SG 552 Commando (stock folded): 504 mm (19.8 in)
SG 553 (stock extended): 730 mm (28.7 in)
SG 553 (stock folded): 501 mm (19.7 in)
SG 550 Sniper (stock extended): 1,130 mm (44.5 in)
SG 550 Sniper (stock folded): 905 mm (35.6 in)
Barrel length SG 550: 528 mm (20.8 in)
SG 551: 363 mm (14.3 in)
SG 552 Commando: 226 mm (8.9 in)
SG 553: 227 mm (8.9 in)
SG 550 Sniper: 650 mm (25.6 in)

Cartridge 5.6mm Gw Pat 90 (5.56x45mm NATO)
Action Gas operated, rotating bolt
Rate of fire Approx. 700 rounds/min
Muzzle velocity SG 550: 911 m/s (2,989 ft/s)
SG 551: 850 m/s (2,788.7 ft/s)
SG 552 Commando: 725 m/s (2,378.6 ft/s)
SG 550 Sniper: 940 m/s (3,084.0 ft/s)
Effective range 100–400 m sight adjustments
Feed system 5, 20, 30-round detachable box magazine
Sights Rear: rotating diopter drum with tritium night inserts; front: hooded post with folding night post
540 mm (21.3 in) sight radius (SG 550)
466 mm (18.3 in) sight radius (SG 551)

The SG 550 is an assault rifle manufactured by Swiss Arms AG (formerly Schweizerische Industrie Gesellschaft) of Neuhausen, Switzerland (SG is an abbreviation for Sturmgewehr, or "assault rifle"). The rifle is based on the earlier 5.56mm SG 540 and is also known as the Fass 90 (Fusil d'assaut 90 / Fucile d'assalto 90) in French / Italian or Stgw 90 in German (Sturmgewehr 90).




In 1978, the Swiss Army formulated requirements for a successor to the Stgw 57 battle rifle (known commercially as the SG 510) using the 7.5x55mm GP11 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-owned Waffenfabrik Bern, using both 6.45x48mm and 5.6x45mm cartridges) and the SG 541 (developed by SIG). In 1981, the experimental 6.45mm GP 80 cartridge was rejected in favor of the more conventional 5.6x45mm GP 90 round (with a 4.1 g, steel-jacketed, lead core projectile) that is the Swiss equivalent to NATO's standard 5.56x45mm 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.

Design details

Operating mechanism

SG 550 disassembled into its main constituent groups

The SG 550 is a selective fire 5.56x45mm NATO assault rifle firing from a closed bolt. It has a gas-actuated piston-driven long stroke operating system derived from the SIG SG 540 series of rifles, which uses burnt powder gases vented through a port in the barrel to power the weapon's moving parts. Once inside the gas cylinder, propellant gases pass through an L-shaped channel machined in the piston head and are directed forward towards the gas valve. The pressure build-up in front of the piston head pushes the piston and bolt carrier rearward. As the piston is driven back, the gas port and the L-shaped channel move out of alignment, cutting off the supply of gas to the cylinder. Surplus gas and powder residues are evacuated through an exhaust port in the gas cylinder. This system ensures that only the precise volume of gas required to overcome the mass and resistance of the rifle's moving assembly is admitted from the barrel. The manually adjustable gas valve has two settings, one for normal operation, and the second setting for use in the presence of heavy fouling or icing.

The rotary bolt locking mechanism consists of two steel locking lugs that engage locking recesses in the breech, and is identical to that used in the SG 540. A spring-loaded extractor is incorporated into the bolt while a fixed protrusion on one of the receiver's internal guide rails ejects the spent cartridge casings.


The ergonomics of the rifle provide the shooter with easy access to various controls. The ambidextrous fire selector/safety is manipulated by the thumb of the shooting hand (the 3 bullet burst mode "3" and the fully automatic "20" position can be disabled by a rotating safety guard to avert accidentally activating the continuous fire mode). The magazines can be stacked using a connector system.
The gas block integrates an adjustable gas regulator, the front sight with a flip-up night sight post, and the bayonet connector on the flash suppressor.
A loaded 20-round magazine. These are made from a translucent durable polymer allowing the shooter to monitor ammunition levels visually.

The rifle is hammer-fired and has a trigger mechanism with an ambidextrous safety and fire selector switch that has 4 settings: "S"—safe, "1"—single fire, "3"—3 round burst and "20"—fully automatic fire. The trigger is enclosed in a pivoting trigger guard which can be folded down to the left or right side allowing for unhindered operation with winter gloves. The trigger pull is approximately 35 N (7.9 lbf)

The firearm is fed by lightweight 20-round box magazines, 30-,10- and 5-round magazines are also available. The magazines are molded from a translucent polymer and can be locked together using studs in order to facilitate quicker reloading; Jungle style. The empty weight of a 20-round magazine is 95 g (3.4 oz) and 110 g (3.9 oz) for a 30-round magazine.

A bolt hold-open device locks the bolt carrier assembly open after expending the last cartridge from the magazine and is released by lifting the bolt catch lever located on the left side of the receiver. Alternatively, a left-handed shooter may release the bolt by pulling the rubber-coated charging handle to rear a short distance.

The SG 550 has a side-folding skeletonized buttstock (folds to the right side of the receiver) and a lightweight aluminium bipod that folds into grooves in the lower handguard. The hinged stock is firmly locked in the folded position by a socket in the butt which clips into a plastic stud on the handguard; a firm pull will release the stock which is then swung into the closed position and locked by a button catch. A collapsible side-folding stock is also available. The stock, pistol grip, and handguards are made of a high-strength polymer, and are produced in either green or black colour options. The steel receiver housing and several other components are manufactured using stamping and welding; external steel surfaces are finished with a ceramic-reinforced enamel coat known as Ilaflon.[1] The gas system's components are made of stainless steel. The barrel, bolt, bolt carrier, and firing pin are all made with steel that has been gas nitrided, hardened and tempered. The bolt and carrier, along with most other components internal to the receiver undergo a phosphating process.

The heavy, cold hammer-forged barrel is screwed into the receiver and is equipped with a slotted "bird cage" type flash suppressor that is also used to launch rifle grenades (using standard, live ammunition) or attach a knife bayonet (the bayonet is supported by a lug located at the base of the gas block). The rifled barrel has 6 right-hand grooves and the Swiss Army specification 254 mm (1:10 in) rifling twist rate is optimized for Swiss military GP 90 ammunition. An export-oriented barrel with a 178 mm (1:7 in) twist rate is also available, designed to stabilize 5.56x45mm NATO rounds with the heavier SS109 projectile.

All rifles are test fired for accuracy and function prior to leaving the factory at the manufacturer's underground 300 m test range. Random new rifles out of production were tested of a machine rest. In a 24 single shot string starting with a cold weapon and using GP 90 ammunition, the 50% windage and elevation dispersion of any individual weapon must have been within an 11 cm (4.3 in) group at 300 m, the 50% windage and elevation dispersion must have averaged 7 cm (2.8 in).[2]


Rotating diopter drum rear sight. The aperture above the "3" (denoting the 300 m setting) can be seen.
Tritium-illuminated night sights. Rear sight at notch "1" with front night sight flipped-up.

The SG 550 series rifles have a 540 mm (21.3 in) long sight radius and are equipped with iron sights adjustable for both windage and elevation. The sights consist of a rear, rotating diopter drum soldered to the receiver and a hooded front post installed in the gas block. The rear sight has an open notch setting marked "1" designed for immediate firing up to 100 m but also contains apertures with settings "2", "3" and "4" corresponding to 200, 300 and 400 m firing ranges. The 400 m setting has a removable iris for sportive shooting. The sights are adjustable via micrometer screws with windage and elevation increments of 1.5 mrad or 4.5 cm (1.8 in) at 300 m. For night use, the dedicated "1" notch setting in the rear sight drum is provided with two self-luminous tritium-powered inserts fitted laterally on each side of the notch and additionally in a flip-up post attached to the foresight. When firing rifle grenades the front sight hood is aligned with the uppermost edge of the grenade's warhead, this provides an estimated point of impact up to 75 m. The rifle grenades intended for this purpose were FN/Luchaire Type 58-N bullet-though anti-tank grenades.

The rifle's sights were placed relatively low over the bore axis to ensure a minimal silhouette when firing from the prone position (the shooter presents a 20% smaller target than with the Stgw 57), but high enough to provide comfort and speed when shouldering the rifle in the kneeling and offhand shooting positions. The design of the shoulder stock also facilitates the rapid alignment of the shooting eye with the rifle's line of sight.

An SG 550 equipped with the Kern 4x24 telescopic sight

For designated marksman use, the SG 550 is equipped with a Kern 4x24 telescopic sight on a quick-detachable mount. The sight weighs 730 g (26 oz) and includes a variety of features, such as STANAG 2324/MIL-STD-1913 compliant mounting components, a Bullet Drop Compensation (BDC) elevation adjustment knob for ranges from 100 to 600 m, a tritium-illuminated reticle that enables target acquisition in low-light conditions and a diopter eyesight correction adjustment. Included with the sight is a lens hood for mounting on the ocular that reduces image quality-impairing stray light and a gray filter for glare reduction.[3] The basic model of this optical sight was already used on the Stgw 57.[4]

The upper receiver can accept quick-detachable rails and adapters used to mount optics (STANAG 2324 compliant). The scope mounting system consists of a centering hole located on the front face of the rear sight assembly and a dovetail-like mounting point at the front end of the receiver. Swiss Arms (respectively Brügger & Thomet) offer several types of quick-release scope mounts and Picatinny rails. A version of the rifle with an integral receiver-mounted Picatinny rail is also offered; in this configuration the weapon is fitted with flip-up emergency battle sights—a rear aperture sight which folds down into a recess in the rail and a folding front blade.


SG 550 with GL 5040 40 mm grenade launcher

Both the rifle and carbine come standard with a spare magazine, sling, cleaning kit and a loading aid for rapid magazine filling.

The firearm will accept SIG's 40 mm GL 5040/5140 grenade launcher (Swiss military designation: 40 mm Gewehraufsatz 97), which is mounted under the barrel via an eccentric latch and replaces the lower handguard. The grenade launcher is a single-shot breech-loaded weapon that is supplied with a leaf sight that attaches to the rifle's rear sight base and enables accurate firing out to 200 m. The lightweight aluminium launcher weighs 1.7 kg (3.7 lb) unloaded, and is operated independently of the rifle. It can use a wide array of 40x46mm grenades, including extended range high-pressure types and non-lethal baton or anti-riot projectiles.

A Stgw 90 bayonet can also be mounted to the rifle. The bayonet has an overall length of 310 mm and a muzzle ring diameter of 22 mm. The 177 mm long blade is single-edged and it has no fuller. The bayonets are manufactured exclusively for the Swiss Army by Wenger and Victorinox (before the two companies merged). With a proper lug adaptor, the rifle will also accept a NATO-pattern KCB-77 (made originally by Carl Eickhorn of Solingen, West Germany) or the American M9.


SG 551

SG 551 carbine

The SG 551 carbine has a short pattern 363 mm (14.3 in) barrel, gas tube and piston compared to the SG 550. The SG 551 series rifles have a 466 mm (18.3 in) long sight radius. The handguards were also changed and the bipod removed. The SG 551 cannot be used with a bayonet or fire rifle grenades. The SG 551 comes in several specialized variants designed for use with security and special forces. Among those variants are the SG 551-1P police carbine (designed to engage point targets out to 300 m; equipped with a Hensoldt 6x42 BL telescopic sight and detachable cheek riser), the SG 551 SWAT carbine (coated with a corrosion-resistant finish and equipped with an optical sight mount used with a wide array of sights, and can also accept mission-critical accessories such as a bipod, laser pointer or tactical light) and the SG 551 LB carbine with an extended 454 mm (17.9 in) barrel that enables the use of rifle grenades and a bayonet.

SG 552 Commando

The compact SG 552 Commando carbine with 30-round magazine

The compact SG 552 Commando carbine was revealed 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.

SG 553

SG 553 in the hands of Malaysian Air Force PASKAU commando during LIMA 2009

The SG 553 is an improved version of the SG 552 and has been released in 2009. 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 like 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) long sight radius. A long barrel version of the SG 553 known as the SG 553 LB incorporates a 347 mm (13.7 in) barrel with provision to fire rifle grenades and support a bayonet. Further factory options for the SG 553 rifle series are an integrated receiver Picatinny rail and an adjustable butt stock.[5]

SG 550 Sniper

Another member of the SG 550 family is the SG 550 Sniper variant designed specifically for Swiss security forces. This accurized rifle has a refined two-stage trigger (the pull force was reduced from 35 N (7.9 lbf) to 15 N (3.4 lbf), a heavy, hammer-forged 650 mm (25.6 in) long barrel with a 254 mm (1:10 in) rifling twist rate (it has no flash hider) and is used exclusively with telescopic sights. The new folding stock has an adjustable cheek piece and a spacer system on the butt, the ergonomic pistol grip's angle of inclination can be regulated and the bipod features a height and cant adjustment mechanism. The rifle is no longer in production.

Civilian variants

The SG 550/551/552/553 are also available in semi-automatic only configurations, intended for the civilian shooting market. Among these variants are the SG 550/551/552 SP, PE 90 and SIG Sport rifles. The SG 550 series is available with either 178 mm or 254 mm (1:7 and 1:10 in) twist rate barrels. Rifles designated SG 55x-1 have a 254 mm (1:10 in) twist rate, while models marked SG 55x-2 have a 178 mm (1:7 in) twist rate. The ordnance GP 90 ammunition is optimized for use with the original Swiss 254 mm (1:10 in) rifling twist rate.

Due to import restrictions, the American civilian market required a partially American-made version assembled by SIG SAUER, Inc. (not to be confused with the Swiss-German entity) in Exeter, New Hampshire. The SIG556 is a commercial variant of the SG 551 designed to meet these requirements. The 556 lacks full-auto capability and the overall length is 940 mm (37.0 in). The main difference is a new aluminum lower receiver that accepts M16 STANAG magazines and an M4 telescoping buttstock. The barrel's twist rate is 178 mm (1:7 in). Most other parts are interchangeable with the SG 550 series.[6]

There are many variants of this rifle offered for sale. The first variant was sold with an aluminum Picatinny rail on the upper receiver and a series of plastic rails on the handguard. The market pushed SIG to produce the rifle with the slimmer profile 551-type handguards and a hooded front sight; this version is marketed as the SIG556 Classic.[7] Several folding stock models have been released as well as variants with railed forend combinations. The most recent major variant is a SIG556 DMR. This features a 21 in (533.4 mm) long barrel without flash suppressor, upgraded, a match type trigger, Magpul PRS stock and older style plastic handguards. SIGP556 pistol or "factory SBR" variants with 10 in barrels are also available.

The SIG522LR is a .22-caliber sporting rifle styled after the SG 551. It uses a simple blowback semi-automatic operating system and its barrel has a 406 mm (1:16 in) twist rate. Due to its operating principle, the rifle has no mechanical commonality with other SG 550 variants. The SIG522 accepts commonly available AR-style .22-caliber conversion magazines.


Swiss Grenadier carrying a Stgw 90 whilst taking part in the Swiss raid commando 2007 competition.


See also


  1. ^ "ILAG Industrielack AG -- Swiss quality coatings". Retrieved 2009-07-09. 
  2. ^ SIG Assault Rifles SG 550 / 551 Technical Data and Test Documentation
  3. ^ SIG 550 bzw. Sturmgewehr 90 (German)
  4. ^ Kern 4x24 telescopic sight of the Swiss Army.
  5. ^ Preisliste_2009
  6. ^ SIG SAUER website
  7. ^ American Rifleman Review of the SIG 556 Classic
  8. ^ Jones, Richard D. Jane's Infantry Weapons 2009/2010. Jane's Information Group; 35 edition (January 27, 2009). ISBN 978-0-7106-2869-5.
  9. ^ "Terre - SIG 551" (in (French)). Retrieved 2009-07-09. 
  10. ^
  11. ^ NSG Aims for Cornershot Weapons, Through the Wall Radars
  12. ^ "Kopassus & Kopaska - Specijalne Postrojbe Republike Indonezije" (in Croatian). Hrvatski Vojnik Magazine. Retrieved 2010-06-12. 
  13. ^ Thompson, Leroy (December 2008). "Malaysian Special Forces". Special Weapons. Retrieved 2009-11-28. 
  14. ^ Zabry Mohamad Madzlan (2008-12-10). "Sig SG 553 is a new rifle for PASKAU". Utusan Malaysia. Retrieved 2009-11-28. 
  15. ^ Wilk (REMOV), Remigiusz. "Nowe gromy GROM". 
  16. ^ "GROM Utility and Equipment". Retrieved 2009-08-02. 
  17. ^ "Špeciálne jednotky Slovenskej republiky". Retrieved 2009-07-09. 
  18. ^ "Web Del Grupo Especial De Operaciones (G.E.O.)". Retrieved 2009-07-09. 
  19. ^ "Web Del Grupo Especial De Operaciones (G.E.O.)". Retrieved 2009-07-09. 
  20. ^ "Sturmgewehr 90 (Stgw 90)". 2008-11-20. Retrieved 2009-07-09. [dead link]
  21. ^ "Exeter's Sigarms gets $115 million federal rifle contract". 2003-07-11. Retrieved 2009-11-17. 


  • Règlement 53.96 Fusil d'assaut 5,6 mm 1990

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