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SIG SG 550 (Sturmgewehr Model 550) / Stgw 90

Assault Rifle / Assault Carbine [ 1990 ]

The SIG SG 550 series has seen widespread use by special forces, regular army and security elements worldwide in its various forms.

Authored By: Staff Writer | Last Edited: 08/10/2023 | Content ©www.MilitaryFactory.com | The following text is exclusive to this site.

The SIG SG 550 (Sturmgewehr Model 550) series was born in a Swiss Army initiative requiring an automatic weapon chambered for the 5.56x45mm NATO cartridge as a replacement for its 1950s-era SIG SG 510 Battle Rifle. Development of the new system began in 1979 and spanned into 1980. After formal evaluations of two competing systems - the W+F C42 from Swiss Federal Arms Factory and the SIG SG 541 - the SIG submission was selected as the winner. Both designs were initially tested with the 6.45mm GP 80 cartridge and the 5.6x45mm GP 90 cartridge (the latter essentially the Swiss version of the 5.56x45mm NATO cartridge) with the 5.6x45 winning out. The SG 541 was adopted as the next standard Swiss Army self-loading weapon system in 1983 (becoming the SG 550 in 1984) and known formally in the Swiss Army inventory as the "Sturmgewehr 90 (Stgw 90)".

The SG 550 was developed into a family of automatic weapons, each born from the basic automatic action and intended to be inherently modular to produce specialized carbine, commando and sniper rifle forms. This benefitted prospective buyers by way of its logistically friendly design that could arm frontline, secondline and specialized forces units as needed - all sharing the same internal components, ammunition and function/training.©MilitaryFactory.com
The SG 550 was designed as an "soldier's weapon" and special care was taken in produce the most lightweight and inexpensive rifle yet one that was utterly reliable and worthy of frontline service. The SG 550 therefore incorporated plastics alongside its metal construction to produce an overall lighter assault weapon. Only key components - those required to absorb the punishment of the firing action - were left metal while the shoulder stock, handguard and magazine were all of plastic. Standard tritium iron sights were fitted for low-level light work though optics could be affixed across the top of the receiver as required. The weapon utilized a gas-operated, rotating bolt action in which the gas cylinder was mounted over the barrel and both of the assemblies were shrouded over by the plastic handguard. The handguard also integrated a folding bipod for the squad support/suppression role. The shoulder stock was skeletal (another weight-saving measure) and designed to fold over the side of the receiver without impeding the functionality of the rifle. Controls of the weapon were fully ambidextrous and included a firing selector with a safety, single-shot, three-round burst and full-automatic mode. The magazines - in 5-, 20- or 30-round counts - were constructed of transparent plastic to allow the operator to receive a quick visual read-out of his existing ammunition supply. Each magazine was also designed with slots to allow several magazines to be clipped together (all standing vertically) for an increased ammunition supply - the operator simply ejecting the spent magazine and sliding the next available magazine into the well. The magazine release lever was situated between the trigger guard and magazine well in the usual way and available mountings allowed use of a bayonet. The muzzle was designed as such that it could fire rifle grenades to further broaden the tactical reach of the standard infantryman.

Despite its extremely promising design, the SG 550 was slow to arrive into Swiss Army service. Budget concerns invariably delayed the arrival of the weapon system to frontline units for several years as funding was diverted to more critical components. Serial production, therefore, did not begin until 1986 and it was only in 1990 that the SG 550 began formal service with the Swiss Army in full. Production of non-military SG 550s is ingoing as of this writing (2012) with some 600,000 examples of all types having been produced to date.

The SG 550 series has been branched out beyond its original full-length assault rifle form to include specialized variants for the discerning customer. Each was more or less faithful in their design to the original SG 550 including internal working components and overall function. The SG 551 became a shortened pattern carbine form of the full-sized 550 complete with a 14-inch barrel and applicably shortened gas cylinder and pistol. This version did, however, lose the capability to fire rifle grenades, mount a bayonet and utilize a folding bipod for obvious reasons. The SG 551-1P (P= "Police") was a police-minded version of the 551 while the SG 551 SWAT was a specialized police version. The SG 551 LB (LP = "Long Barrel") was yet another carbine derivative though with an 18-inch barrel which retained the capability to fire rifle grenades and mount a bayonet. All carbine versions accepted a 20- or 30-round magazine.

In 1998, the SG 550 family was further developed into a more compact version as the SG 552 "Commando" with the police version being the SG 552-2P. This form included a 9-inch barrel and reworked internals due to its reduced overall size. There also existed the SG 552 LB long-barrel form with its 13.6 inch barrel assembly. In 2009, SIG released the improved compact SG 553 with 13.7 inch barrel, adjustable shoulder stock and Picatinny rail accessories support. Internals were reworked to match more closely that of the original SG 550 mark.

A dedicated sharpshooting platform was unveiled as the SG 550 "Sniper" with appropriate modifications for the accuracy-minded, long-range role. This variant included a longer barrel of heavy-duty construction, an adjustable butt with cheekpiece, a two-stage trigger, a well-molded pistol grip and support for a variety of optics. This mark lacked the basic iron sights as optics were expected to be a part of the complete weapon system for obvious reasons. Magazine counts included a 5-round and 20-round form.

The SG 550 was inevitably released to the commercial market and limited to semi-automatic fire forms. As such, they fit the bill well for civilian customers and police force, the latter generally not requiring use of full-automatic weapons. "Americanized" versions were seen with STANAG magazines and featured an M4 Carbine-style collapsible (telescoping) stock while a sporting-minded version - the SIG522LR - was chambered for the .22 cartridge.

The SIG 550 family enjoys widespread use in the army, police and security forces of the world. Operators include Argentina, Brazil, France (as the Fass 90), Germany, India, Indonesia, Macau, Malaysia, Malta, Poland (GROM), Serbia, Slovakia, Spain, Switzerland, Turkey and the United States (solely the DEA).©MilitaryFactory.com
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Service Year

Switzerland national flag graphic


Assault Rifle / Assault Carbine

SIG-Sauer / Swiss Arms AG - Switzerland
(View other Arms-Related Manufacturers)
National flag of Argentina National flag of Brazil National flag of Egypt National flag of France National flag of modern Germany National flag of India National flag of Indonesia National flag of Malaysia National flag of Pakistan National flag of the Philippines National flag of Poland National flag of Serbia National flag of Slovakia National flag of Spain National flag of Switzerland National flag of Turkey National flag of the United States Argentina; Brazil; Egypt; France; Germany; India; Indonesia; Macau; Malaysia; Malta; Pakistan; Philippines; Poland; Serbia; Slovakia; Spain; Switzerland; Turkey; United States
(OPERATORS list includes past, present, and future operators when applicable)
Automatic Function
Features a mechanical function to automate the firing action.
Assault Rifle
Modern class of long gun featuring select-fire properties, automatic internal function, and magazine feeding.
Accuracy / Precision
Long-range accuracy / precision capable; suitable for sniping, particularly when equipped with sighting aids.

Overall Length
998 mm
39.29 in
Barrel Length
528 mm
20.79 in
Empty Wgt
9.04 lb
4.10 kg

Iron Front and Rear; Optional Optics


Gas-Operated; Rotating Bolt

Rotating Bolt
System utilizes internal mechanism to lock the breech or rear barrel assembly prior to firing.
Gas-operated system is featured, typically involving a gas cylinder and rear-driven piston directing energy to the bolt component.
(Material presented above is for historical and entertainment value and should not be construed as usable for hardware restoration, maintenance, or general operation - always consult official manufacturer sources for such information)


5.56x45mm NATO

Sample Visuals**

Graphical image of a 5.56mm intermediate rifle cartridge
Rounds / Feed

5-, 20- or 30-round detachable box magazine
Cartridge relative size chart
*May not represent an exhuastive list; calibers are model-specific dependent, always consult official manufacturer sources.
**Graphics not to actual size; not all cartridges may be represented visually; graphics intended for general reference only.
Max Eff.Range
1,312 ft
(400 m | 437 yd)
Muzzle Velocity
2,989 ft/sec
(911 m/sec)

SG 550 - Swiss Designation; base production model.
SG 551 - Carbine based on the full-length SG 550; 14.3-inch barrel; revised handguard; sans bipod; sans support for rifle grenades and bayonet.
SG 551-1P - Police version of SG 551
SG 551 "SWAT" - SWAT version of SG 551
SG 551 LB ("Long Barrel") - 17.9-inch barrel; support for rifle grenades and bayonet.
SG 552 "Commando" - Compact Carbine Form; 8.9-inch barrel; reworked internals; appearing in 1998.
SG 552-2P - Police bersion of SG 552 Commando
SG 552 LB ("Long Barrel") - Variant of SG 552 with 13.6-inch barrel; compatible with rifle grenades and bayonet.
SG 553 - Improved SG 552; internals follow SG 550 models; 13.3-inch barrel; appearing in 2009.
SG 553 LB ("Long Barrel") - 13.7-inch barrel; Picatinny rail; support for rifle grenades and bayonet.
SG 550 "Sniper" - Dedicated marksman rifle form; two-stage trigger; 25.6-inch heavy barrel; sans iron sights; 5- or 20-round magazine; bipod; adjustable shoulder stock; new ergonomic pistol grip.
Fass 90 - French Army Designation of SG 550
Stgw 90 - German Army Designation of SG 550
SG 550 "Sport" - Civilian Rifle Form
SIG 556 - American Commercial Market Variant
SIG 522LR - Chambered for the .22 cartridge; blowback operation.
SG 550 SP - Civilian version of SG 550; semi-automatic fire only.
SG 551 SP - Civilian version of SG 551; semi-automatic fire only.
SG 552 SP - Civilian version of SG 552; semi-automatic fire only.
PE 90
SIG556 "Classic" - Slim profile variant; Picatinny rail.
SIG556 DMR - 21-inch barrel; Magpul stock.
SIGP556 - Pistol Variantl 10-inch barrel

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Image of the SIG SG 550 (Sturmgewehr Model 550) / Stgw 90
Right side view of the Swiss SIG SG 550 assault rifle; note collapsed bipod under the handguard

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