SIG SG 550
Encyclopedia
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).
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.
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 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. 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 grenade
s (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).
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.
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 (25.7 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. The basic model of this optical sight was already used on the Stgw 57.
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 rail
s. 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.
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
.
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.
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.
and an adjustable butt stock.
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 in). The main difference is a new aluminum lower receiver that accepts M16
STANAG magazine
s 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.
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. 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.
Assault rifle
An assault rifle is a selective fire rifle that uses an intermediate cartridge and a detachable magazine. Assault rifles are the standard infantry weapons in most modern armies...
manufactured by Swiss Arms AG
Swiss Arms
SAN Swiss Arms AG is a Swiss manufacturer of small arms. It was known as SIG Arms AG before 2000 when it was acquired by the German investors Michael Lüke and Thomas Ortmeier from parent company Schweizerische Industrie Gesellschaft .-Products:...
(formerly Schweizerische Industrie Gesellschaft
Schweizerische Industrie Gesellschaft
Schweizerische Industrie Gesellschaft , or SIG, is the former name of SIG Holding AG, a Swiss company that has been active in various businesses during its more than 150 years of operation. Since the year 2000 the Society has undergone strategic refocus, concentrating on its core compentence in...
) of Neuhausen
Neuhausen am Rheinfall
Neuhausen am Rheinfall is a municipality in the canton of Schaffhausen in Switzerland.The little town is well known for the Rhine Falls, a tourist attraction and mainland Europe's largest waterfall....
, Switzerland
Switzerland
Switzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....
(SG is an abbreviation for Sturmgewehr, or "assault rifle"). The rifle is based on the earlier 5.56mm
5.56x45mm NATO
5.56×45mm NATO is a rifle cartridge developed in the United States and originally chambered in the M16 rifle. Under STANAG 4172, it is a standard cartridge for NATO forces as well as many non-NATO countries. It is derived from, but not identical to, the .223 Remington cartridge...
SG 540
SIG SG 540
The SG 540 is a 5.56mm assault rifle developed in the early 1970s by Schweizerische Industrie Gesellschaft based out of Neuhausen, Switzerland as a private venture primarily destined for export markets and as a potential replacement for the 7.5mm SG 510 automatic rifle known as the Stgw 57 in...
and is also known as the Fass 90 (Fusil d'assaut 90 / Fucile d'assalto 90) in French
French language
French is a Romance language spoken as a first language in France, the Romandy region in Switzerland, Wallonia and Brussels in Belgium, Monaco, the regions of Quebec and Acadia in Canada, and by various communities elsewhere. Second-language speakers of French are distributed throughout many parts...
/ Italian
Italian language
Italian is a Romance language spoken mainly in Europe: Italy, Switzerland, San Marino, Vatican City, by minorities in Malta, Monaco, Croatia, Slovenia, France, Libya, Eritrea, and Somalia, and by immigrant communities in the Americas and Australia...
or Stgw 90 in German
German language
German is a West Germanic language, related to and classified alongside English and Dutch. With an estimated 90 – 98 million native speakers, German is one of the world's major languages and is the most widely-spoken first language in the European Union....
(Sturmgewehr 90).
Development
In 1978, the Swiss ArmyMilitary of Switzerland
The Swiss Armed Forces perform the roles of Switzerland's militia and regular army. Under the country's militia system, professional soldiers constitute about 5 percent of military personnel; the rest are male citizen conscripts 19 to 34 years old...
formulated requirements for a successor to the Stgw 57 battle rifle
Battle rifle
A battle rifle is a military service rifle that fires a full power rifle cartridge, such as 7.62x51mm NATO. While the designation of battle rifle is usually given to post-World War II select fire infantry rifles such as the H&K G3, the FN FAL or the M14, this term can also apply to older military...
(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
Carbine
A carbine , from French carabine, is a longarm similar to but shorter than a rifle or musket. Many carbines are shortened versions of full rifles, firing the same ammunition at a lower velocity due to a shorter barrel length....
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
W+F C42
The C42 was a prototype assault rifle manufactured by W+F Bern of Switzerland as an entry in a competition for a new Swiss Army service rifle . It was chambered in 5.56x45mm NATO and 6.8mm SPC in and designed in conventional as well as bullpup layouts. As the competition was won by what became the...
(developed by the state-owned Waffenfabrik Bern
Waffenfabrik Bern
Waffenfabrik Bern, also known as W+F Bern, was an arms manufacturer in Bern, Switzerland and was a government-owned corporation.-List of W+F weapons:*Vetterli rifle*Schmidt M1882 1882 revolver. Chambered in 7.5 Swiss Ordnance...
, 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
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
-jacketed, lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
core projectile) that is the Swiss equivalent to NATO's standard 5.56x45mm
5.56x45mm NATO
5.56×45mm NATO is a rifle cartridge developed in the United States and originally chambered in the M16 rifle. Under STANAG 4172, it is a standard cartridge for NATO forces as well as many non-NATO countries. It is derived from, but not identical to, the .223 Remington cartridge...
cartridge.
Production
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.Operating mechanism
The SG 550 is a selective fireSelective fire
A selective fire firearm has at least one semi–automatic and one automatic mode, which is activated by means of a selector which varies depending on the weapon's design. Some selective fire weapons utilize burst fire mechanisms to limit the maximum or total number of shots fired automatically in...
5.56x45mm NATO
5.56x45mm NATO
5.56×45mm NATO is a rifle cartridge developed in the United States and originally chambered in the M16 rifle. Under STANAG 4172, it is a standard cartridge for NATO forces as well as many non-NATO countries. It is derived from, but not identical to, the .223 Remington cartridge...
assault rifle
Assault rifle
An assault rifle is a selective fire rifle that uses an intermediate cartridge and a detachable magazine. Assault rifles are the standard infantry weapons in most modern armies...
firing from a closed bolt
Closed bolt
A semi or full-automatic firearm which is said to fire from a closed bolt is one where, when ready to fire, a round is in the chamber and the bolt and working parts are forward...
. It has a gas-actuated
Gas-operated reloading
Gas-operation is a system of operation used to provide energy to operate autoloading firearms. In gas-operation, a portion of high pressure gas from the cartridge being fired is used to power a mechanism to extract the spent case and chamber a new cartridge. Energy from the gas is harnessed...
piston-driven long stroke operating system derived from the SIG SG 540
SIG SG 540
The SG 540 is a 5.56mm assault rifle developed in the early 1970s by Schweizerische Industrie Gesellschaft based out of Neuhausen, Switzerland as a private venture primarily destined for export markets and as a potential replacement for the 7.5mm SG 510 automatic rifle known as the Stgw 57 in...
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
Rotating bolt
Rotating bolt is a method of locking originally developed by Ferdinand Ritter von Mannlicher and found in his Steyr-Mannlicher M1895 straight-pull bolt-action rifle designed for and issued to the Austro-Hungarian Army...
locking mechanism consists of two steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
locking lugs that engage locking recesses in the breech, and is identical to that used in the SG 540. A spring-loaded extractor
Extractor (firearms)
An extractor is a part in a firearm that serves to remove brass cases of fired ammunition after the ammunition has been fired. When the gun's action cycles, the extractor lifts or removes the spent brass casing from the firing chamber.-Overview:...
is incorporated into the bolt while a fixed protrusion on one of the receiver's internal guide rails ejects the spent cartridge casings.
Features
The firearm is fed by lightweight 20-round box magazines, 30-,10- and 5-round magazines are also available. The magazines are molded
Injection molding
Injection molding is a manufacturing process for producing parts from both thermoplastic and thermosetting plastic materials. Material is fed into a heated barrel, mixed, and forced into a mold cavity where it cools and hardens to the configuration of the cavity...
from a translucent polymer and can be locked together using studs in order to facilitate quicker reloading; Jungle style
Jungle style
The term "Jungle Style" usually refers to the practice of taping or securing two gun magazines together, with one taped upside down while the other is inserted into the rifle. However, a rifle may also be jungle styled by using plastic divider or cradle in which the two magazines sit, usually upright...
. 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
Stock (firearm)
A stock, also known as a buttstock or shoulder stock, is a part of a rifle or other firearm, to which the barrel and firing mechanism are attached, that is held against one's shoulder when firing the gun. Stocks are also found on crossbows though a crossbow stock is more properly referred to as a...
(folds to the right side of the receiver) and a lightweight aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
bipod
Bipod
A bipod is a support device that is similar to a tripod or monopod, but with two legs. It provides significant stability along two axes of motion .-Firearms:...
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
Pistol grip
On a firearm or other tool, the pistol grip is that portion of the mechanism that is held by the hand and orients the hand in a forward, vertical orientation, similar to the position one would take with a conventional pistol such as the M1911....
, and handguards are made of a high-strength polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
, and are produced in either green or black colour options. The steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
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. The gas system's components are made of stainless steel
Stainless steel
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....
. The barrel, bolt, bolt carrier, and firing pin are all made with steel that has been gas nitrided
Nitridization
Nitriding is a heat treating process that diffuses nitrogen into the surface of a metal to create a case hardened surface. It is predominantly used on steel, but also titanium, aluminum and molybdenum....
, hardened and tempered. The bolt and carrier, along with most other components internal to the receiver undergo a phosphating
Parkerizing
Parkerizing is a method of protecting a steel surface from corrosion and increasing its resistance to wear through the application of an electrochemical phosphate conversion coating...
process.
The heavy, cold hammer-forged barrel is screwed into the receiver and is equipped with a slotted "bird cage" type flash suppressor
Flash suppressor
A flash suppressor, also known as a flash guard, flash eliminator, flash hider, or flash cone, is a device attached to the muzzle of a rifle or other gun that reduces the visible signature of the burning gases that exit the muzzle. This reduces the chances that the shooter will be blinded in dark...
that is also used to launch rifle grenade
Rifle grenade
A rifle grenade is a grenade that uses a rifle-based launcher to permit a longer effective range than would be possible if the grenade was thrown by hand...
s (using standard, live ammunition) or attach a knife bayonet
Bayonet
A bayonet is a knife, dagger, sword, or spike-shaped weapon designed to fit in, on, over or underneath the muzzle of a rifle, musket or similar weapon, effectively turning the gun into a spear...
(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).
Sights
The rifle's sights were placed relatively low over the bore axis to ensure a minimal silhouette when firing from the prone position
Prone position
The term means to lie on bed or ground in a position with chest downwards and back upwards.-Etymology :The word "prone," meaning "naturally inclined to something, apt, liable," has been recorded in English since 1382; the meaning "lying face-down" was first recorded in 1578, but is also referred to...
(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
Kneeling position
The kneeling position is a position for rifle shooting. There are no longer international competitions in pure kneeling shooting, but it is included as the last part of 300 metre rifle three positions, 300 metre standard rifle and 50 metre rifle three positions.It takes a very long time to achieve...
and offhand
Standing position
In shooting, the standing position, also known as "offhand", refers to shooting while standing. It is often regarded as the most difficult position. The rules vary depending on the shooting discipline. Generally, one must stand freely, without the aid of a rest or bench. Highpower rifle, smallbore...
shooting positions. The design of the shoulder stock also facilitates the rapid alignment of the shooting eye with the rifle's line of sight.
Telescopic sight
A telescopic sight, commonly called a scope, is a sighting device that is based on an optical refracting telescope. They are equipped with some form of graphic image pattern mounted in an optically appropriate position in their optical system to give an accurate aiming point...
on a quick-detachable mount. The sight weighs 730 g (25.7 oz) and includes a variety of features, such as STANAG 2324/MIL-STD-1913
Picatinny rail
The Picatinny rail or MIL-STD-1913 rail or STANAG 2324 rail or a "Tactical Rail" is a bracket used on some firearms in order to provide a standardized mounting platform. A similar system is the Weaver rail mount.-Description:...
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. The basic model of this optical sight was already used on the Stgw 57.
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
Dovetail
Dovetail may refer to:* The dovetail joint used in woodworking* The dovetail or "riffle" method of shuffling playing cards* German equatorial mount, or dovetail plate, used to fix a telescope to its mount...
-like mounting point at the front end of the receiver. Swiss Arms (respectively Brügger & Thomet
Brügger & Thomet
Brügger & Thomet AG is a licensed Swiss defense supplier specializing in the design and manufacturing of firearms and tactical components such as sound suppressors and rail systems. The company is located in Thun, Switzerland. B&T consists of a trading and manufacturing division...
) offer several types of quick-release scope mounts and Picatinny rail
Picatinny rail
The Picatinny rail or MIL-STD-1913 rail or STANAG 2324 rail or a "Tactical Rail" is a bracket used on some firearms in order to provide a standardized mounting platform. A similar system is the Weaver rail mount.-Description:...
s. 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.
Accessories
Sling (firearms)
In the context of firearms, a sling is a type of strap or harness designed to allow a shooter to carry a firearm on his/her person and/or aid in greater hit probability with that firearm...
, cleaning kit and a loading aid for rapid magazine filling.
The firearm will accept SIG's 40 mm GL 5040/5140
SIG GL 5040
The SIG GL 5040/5140 is a 40 mm grenade launcher, which can be mounted under all SIG SG 550/551 assault rifle models and is operated in single-shot mode.-Users:: The Swiss military in-service designation for the GL 5040 is 40 mm Gewehraufsatz 97....
grenade launcher
Grenade launcher
A grenade launcher or grenade discharger is a weapon that launches a grenade with more accuracy, higher velocity, and to greater distances than a soldier could throw it by hand....
(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
Breech-loading weapon
A breech-loading weapon is a firearm in which the cartridge or shell is inserted or loaded into a chamber integral to the rear portion of a barrel....
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
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
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
Bayonet
A bayonet is a knife, dagger, sword, or spike-shaped weapon designed to fit in, on, over or underneath the muzzle of a rifle, musket or similar weapon, effectively turning the gun into a spear...
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
Fuller (weapon)
A fuller is a rounded or beveled groove or slot in the flat side of a blade . A fuller is often used to lighten the blade, much in the way that an I-beam shape allows a given amount of strength to be achieved with less material...
. The bayonets are manufactured exclusively for the Swiss Army by Wenger
Wenger
Wenger is one of two companies that have manufactured Swiss Army knives. Based in Delémont, Wenger was acquired by rival Victorinox in 2005.- History :The history of Wenger S.A...
and Victorinox
Victorinox
Victorinox is a knife manufacturer based in the town of Ibach, in the Canton of Schwyz, Switzerland. Since its acquisition of rival Wenger in 2005, it has, once more, become the sole supplier of multi-purpose knives to the Swiss army.-History:...
(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
Solingen
Solingen is a city in North Rhine-Westphalia, Germany. It is located on the northern edge of the region called Bergisches Land, south of the Ruhr area, and with a 2009 population of 161,366 is the second largest city in the Bergisches Land...
, West Germany
West Germany
West Germany is the common English, but not official, name for the Federal Republic of Germany or FRG in the period between its creation in May 1949 to German reunification on 3 October 1990....
) or the American M9
M9 Bayonet
The M9 Bayonet is a multi-purpose knife and bayonet officially adopted in 1984 by the United States. It has a blade and is issued with a sheath designed to double as a wire cutter. It was designed and developed by Charles A. "Mickey" Finn at his R&D company, Qual-A-Tec. He later produced it under...
.
SG 551
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 sightTelescopic sight
A telescopic sight, commonly called a scope, is a sighting device that is based on an optical refracting telescope. They are equipped with some form of graphic image pattern mounted in an optically appropriate position in their optical system to give an accurate aiming point...
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
AK-47
The AK-47 is a selective-fire, gas-operated 7.62×39mm assault rifle, first developed in the Soviet Union by Mikhail Kalashnikov. It is officially known as Avtomat Kalashnikova . It is also known as a Kalashnikov, an "AK", or in Russian slang, Kalash.Design work on the AK-47 began in the last year...
: 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
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 railPicatinny rail
The Picatinny rail or MIL-STD-1913 rail or STANAG 2324 rail or a "Tactical Rail" is a bracket used on some firearms in order to provide a standardized mounting platform. A similar system is the Weaver rail mount.-Description:...
and an adjustable butt stock.
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-automaticSemi-automatic firearm
A semi-automatic, or self-loading firearm is a weapon which performs all steps necessary to prepare the weapon to fire again after firing—assuming cartridges remain in the weapon's feed device or magazine...
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
Exeter, New Hampshire
Exeter is a town in Rockingham County, New Hampshire, United States. The town's population was 14,306 at the 2010 census. Exeter was the county seat until 1997, when county offices were moved to neighboring Brentwood...
. 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 in). The main difference is a new aluminum lower receiver that accepts M16
M16 rifle
The M16 is the United States military designation for the AR-15 rifle adapted for both semi-automatic and full-automatic fire. Colt purchased the rights to the AR-15 from ArmaLite, and currently uses that designation only for semi-automatic versions of the rifle. The M16 fires the 5.56×45mm NATO...
STANAG magazine
STANAG magazine
A STANAG magazine is a type of detachable firearm magazine proposed by NATO in October 1980. Shortly after NATO's acceptance of the 5.56x45mm NATO rifle cartridge, Draft Standardization Agreement 4179 was proposed in order to allow the military services of member nations easily to share rifle...
s and an M4
M4 carbine
The M4 carbine is a family of firearms tracing its lineage back to earlier carbine versions of the M16, all based on the original AR-15 designed by Eugene Stoner and made by ArmaLite. It is a shorter and lighter variant of the M16A2 assault rifle, with 80% parts commonality.It is a gas-operated,...
telescoping buttstock. The barrel's twist rate is 178 mm (1:7 in). Most other parts are interchangeable with the SG 550 series.
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. 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
Magpul Industries
Magpul Industries Corporation is a designer and manufacturer of polymer firearms accessories and concept firearms. The company is based in Erie, Colorado in the United States...
PRS stock and older style plastic handguards. SIGP556 pistol or "factory SBR
Short barreled rifle
Short-barreled rifle is a legal designation in the United States, referring to a shoulder-fired, rifled firearm with a barrel length of less than 16 inches or overall length of less than 26 inches . In the United States, an SBR is an item regulated by the Bureau of Alcohol, Tobacco, Firearms and...
" variants with 10 in barrels are also available.
The SIG522LR is a .22
.22 Long Rifle
The .22 Long Rifle rimfire cartridge is a long established variety of ammunition, and in terms of units sold is still by far the most common in the world today. The cartridge is often referred to simply as .22 LR and various rifles, pistols, revolvers, and even some smoothbore shotguns have...
-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.
Users
- Uses the SG 550 and SG 551 variants.: The SG 551 and SG 551 LB carbines are used by some specialized units of the French ArmyFrench ArmyThe French Army, officially the Armée de Terre , is the land-based and largest component of the French Armed Forces.As of 2010, the army employs 123,100 regulars, 18,350 part-time reservists and 7,700 Legionnaires. All soldiers are professionals, following the suspension of conscription, voted in...
.: The German Federal Police'sGerman Federal PoliceThe Bundespolizei is a uniformed federal police force in Germany. It is subordinate to the Federal Ministry of the Interior...
counter-terrorism unit GSG 9GSG 9The GSG 9 der Bundespolizei , is the elite counter-terrorism and special operations unit of the German Federal Police.-History and name:...
and the SpezialeinsatzkommandoSpezialeinsatzkommandoSpezialeinsatzkommandos are the special response units of the German state police forces. German SEKs are full-time units whose members do not perform any other duties, and are essentially the equivalent of American SWAT Teams...
groups of some state police forcesLandespolizeithumb|[[Germany|German]] police officer in [[Hamburg]]The Landespolizei are the main police forces of Germany. They are under the sole jurisdiction, funded and operated by the states of Germany.-History:...
employ the SG 551 and SG 551 LB carbines in a variety of roles under the designation G37.: Used by the National Security Guard (NSG).: SG 550 and SG 552 variants are used by the Komando Pasukan KatakKOPASKAKopaska or Komando Pasukan Katak is the premier frogman and underwater demolition unit of the Indonesian Navy. The Unit's motto is 'Tan Hana Wighna Tan Sirna', which means 'There is no obstacle that can not be defeated'. It was officially established on March 31, 1962 by President Sukarno to help...
(Kopaska) tactical diver group and Komando Pasukan KhususKopassusKopassus is an Indonesian Army special forces group that conducts special operations missions for the Indonesian government, such as direct action, unconventional warfare, sabotage, counter-insurgency, counter-terrorism, and intelligence gathering.Kopassus was founded on April 16, 1952...
(Kopassus) special forces group.: The Royal Malaysian Air Force's counter-terrorism unit PASKAUPaskauPaskau may refer to:* PASKAU, a special forces unit of the Royal Malaysian Air Force* the town of Paskov in the Czech Republic...
employ the SG 552 and SG 553 LB/SB carbines.: Grupa Reagowania Operacyjno-ManewrowegoGROMGROM is one of five special forces units of the Polish Armed Forces. It was officially activated on July 8, 1990...
(GROM) special forcesSpecial forcesSpecial forces, or special operations forces are terms used to describe elite military tactical teams trained to perform high-risk dangerous missions that conventional units cannot perform...
group.: The Slovak Police Útvar Osobitného Určenia ("special assignments unit") utilizes the SG 551 SWAT carbine.: National police GEOGrupo Especial de OperacionesThe Grupo Especial de Operaciones , commonly known as GEOs, are the Special Operations Forces of the Spanish Cuerpo Nacional de Policía of Spain. They are stationed in Guadalajara near the capital, Madrid. The GEO has response capabilities and is responsible for VIP protection duties, as well as...
special operations group uses both the SG 551 SWAT and SG 552.: The SG 550 is the standard service rifle of the Swiss Armed Forces.: Used by some federal agencies such as the Drug Enforcement AdministrationDrug Enforcement AdministrationThe Drug Enforcement Administration is a federal law enforcement agency under the United States Department of Justice, tasked with combating drug smuggling and use within the United States...
(SG 551).
External links
- Swiss Arms AG—manufacturer's site
- Swiss Arms brochure
- Swiss Arms PE 90 brochure
- Modern Firearms
- Biggerhammer.net—portal for articles, information and manuals, etc. on the SIG Stgw 57/SG 510/AMT and SG 550 rifle series
- SG 550/551 technical data and test documentation
- The SIG SG 550 series—information, manuals and links
- SG 550/551 instruction manual
- SG 552 instruction manual
- Swiss Armed Forces Stgw 90 manual