SIG SG 550 (Sturmgewehr Model 550) / Stgw 90

History of SIG SG 550 (Assault Rifle Model 550)/Stgw 90

The SIG SG 550 series (Assault Rifle Model 550) originated from a Swiss Army program to develop an automatic weapon for the 5.56 x 45 mm NATO cartridge to replace the SIG SG 510 battle rifle requirement in the 1950s . Development of the new system started in 1979 and continued until 1980. The SIG submission was selected as the winner after a formal evaluation of two competing systems - the Swiss Federal Armament Factory's W+F C42 and SIG SG 541. Both designs were initially tested using the 6.45mm GP-80 cartridge and the 5.6x45mm GP-90 cartridge (the latter being essentially the Swiss version of the 5.56x45mm NATO cartridge), with the 5.6x45 predominant.

The SG 541 was introduced in 1983 as the Swiss Army's next standard self-loading weapon system (it became the SG 550 in 1984) and was officially known as the "Assault Rifle 90 (Stgw 90)" in the Swiss Army inventory.

The SG 550 was developed into a range of automatic weapons, each evolving from a basic automatic action and designed to be modular in nature to produce specialized carbine, commando and sniper rifle forms. Potential buyers benefit from its logistically friendly design that can arm frontline, secondary and special forces as needed - all with the same internal components, ammunition and functionality/training.

The SG 550 is considered a "soldier's weapon" and special care is taken to produce the lightest and most affordable rifle, yet it is completely reliable and suitable for use on the front lines. Therefore, the SG 550 integrates plastic in addition to the metal structure to produce an overall lighter offensive weapon.

Only the key partsthose that need to absorb the penalty of the shooting actionare metal, while the shoulder rests, handguards, and magazines are all plastic. Standard tritium sights are good for low light work, but optics can be mounted on top of the receiver if desired.

The weapon uses a pneumatic rotating bolt breech, the gas cylinder is mounted above the barrel, and both components are housed in a plastic handguard. The handguard also contains a foldable bipod for squad support/suppression.

The shoulder rest is skeletal (another weight saving measure) designed to fold over the side of the receiver without sacrificing rifle functionality. Weapon controls are fully ambidextrous, including a fire selector switch with safe, single-shot, triple-shot burst and fully automatic modes. These magazines - 5, 20 or 30 rounds - are made of clear plastic, allowing the operator to quickly visualize his existing ammunition supply. Each magazine is also designed with slots to allow multiple magazines (all positioned vertically) to be clipped together to increase ammo supply - the operator simply ejects the used magazine and slides the next available magazine into the insert groove.

As usual, the magazine release lever is located between the trigger guard and the magazine well, and the available mount allows the use of a bayonet. The muzzle is designed to fire rifle grenades to further extend the tactical range of standard infantry.

Despite its very promising design, the SG 550 was slow to enter service with the Swiss Army. Budget issues invariably delay the arrival of weapons systems to frontline troops by several years as funds are diverted to more critical components. As a result, serial production only started in 1986, and it was not until 1990 that the SG 550 entered full service with the Swiss Army.

As of this writing (2012), production of the non-military SG 550 is still in progress, with around 600,000 examples of all types produced to date.

The SG 550 series has moved beyond its original full-length assault rifle form to offer specialized variants for discerning customers. Each is more or less faithful to the original SG 550's design, including the inner working components and overall functionality. The SG 551 became a shortened carbine form of the full-size 550 with a 14-inch barrel and correspondingly shortened cylinder and pistol.

However, for obvious reasons, this version lost the ability to fire rifle grenades, mount bayonets and use a foldable bipod. The SG 551-1P (P = "Police") is the police version of the 551, while the SG 551 SWAT is a dedicated police version. However, the SG 551 LB (LP = "Long Barrel") is another carbine derivative with an 18-inch barrel that retains the ability to fire rifle grenades and mount a bayonet.

All carbine versions accept 20 or 30 round magazines.

In 1998, the SG 550 series was further developed into a more compact version, the SG 552 "Commando", and the police version as the SG 552-2P. This form has a 9-inch barrel and improved internals due to the reduced overall size. There is also the SG 552 LB off-road form with a 13.6" barrel.

In 2009, SIG released an improved compact SG 553 with a 13.7" barrel, adjustable stock and Picatinny rail accessory support. The interior has been revised to better match the original SG 550 branding.

As the SG 550 "Sniper", a dedicated sniper platform appropriately modified for precise long-range roles was introduced. This variant features a longer barrel, solid construction, an adjustable stock with cheek plates, a two-stage trigger, a well-shaped pistol grip and mounts for various optics.

This brand lacks basic iron sights, for obvious reasons, optics should be part of the overall weapon system. Journal counts include 5-round and 20-round formats.

The SG 550 was released mandatory for the commercial market, limited to firepower in semi-automatic form. As such, they are ideal for civilian customers and law enforcement, which generally do not require the use of fully automatic weapons.

The "Americanized" version appeared in STANAG magazine with a collapsible (telescopic) M4 carbine stock, while the sport-oriented version - SIG522LR - was designed for .22 cartridges.

The SIG 550 series is used worldwide by the military, police and security forces. Operators include Argentina, Brazil, France (e.g. Fass 90), Germany, India, Indonesia, Macau, Malaysia, Malta, Poland (GROM), Serbia, Slovakia, Spain, Switzerland, Turkey and the United States (DEA only).

Specification

Roles

Dimensions

Performance

Changes