SIG SG 550/551

A superior concept, programmed for success The new SIG assault rifle series SG 550/551 are built and tested in accordance with state-of-the-art manufacturing and quality assurance criteria. The design concept employs the proven combination of gas operation and rotating bolt, providing the weapons with utmost dependability, even under the most extreme field conditions. These new SIG assault rifles are available in two versions: the standard model SG 550 and the SG 551 short pattern. As such, they effectively form a weapon family, sharing a majority of common components. Consequently, handling, training and maintenance are identical for both models. The standard version is equipped with a bipod. Given the optimal weapon layout, accurate shooting in all positions is enhanced. The heavy barrel, hammer-forged in one operation to form chamber and bore, the long sight base and the carefully matched sighting elements provide superior inherent accuracy. The functionally mature and weight-saving design concept provides advantages such as increased combat readiness plus additional features such as 3-round burst, folding butt and bolt hold-open catch. Highly accurate, lightweight and rugged SIG's state-of-the-art production processes and manufacturing know-how guarantee their weapons' superior quality and combat readiness. In practical terms this represents: extreme precision, low weight factor and ruggedness. As with all previous SIG assault rifles, the SG 550/551 are simple and safe handling weapons that have been proven in troop trials to be functionally dependable. The SIG assault rifles SG 550/551 can be operated with one hand by both left- and right-handed shooters. The ambidextrous selective-fire catch can be operated with the shooting hand, thus eliminating any need to change position. Spent casings are ejected approximately five meters forward of the shooter, thereby eliminating the need for any type of case deflector. Another convincing feature is the system of lightweight, transparent magazines which can be clipped together and changed rapidly. Rifle grenades are launched with standard, live ammunition. The weapon cycles automatically and therefore remains operational at all times. All weapons are designed to accept night vision equipment and telescopic sights (STANAG system). To this end, a quick-detach scope mount is available which directly accepts STANAG-based optics. Its precision fit ensures zero-retention even after repeated mountings. Mounted on the receiver housing is a combined diopter and snapshooting rearsight assembly which is calibrated for selected ranges. It is adjustable to provide windage and elevation correction. For night firing, illuminated markings are standard. Consequently, when adjustments are made to the day sights, correction of the night markings is automatic. The foresight assembly, comprising the protective tunnel and the flip-up night sight with integrated light source, is fixed. As the overall sighting line is low, the exposure silhouette presented by the shooter is minimized. The new models SG 550/551 SP meet NATO test specifications and all other demanding requirements imposed for an optimal infantry weapon, namely: Exceptional accuracy Heavy, fixed barrel with chamber and bore hammer-forged simultaneously Excellent trigger that breaks crisp and clean after taking the slack out Optimal diopter and snapshooting sights, adjustable for windage and elevation On-the-weapon folding bipod fitted into a recessed handguard (SG 550 SP) Reliable functioning Rugged, yet simple, design concept employing a proven gas system and rotating bolt Virtually closed weapon system Night Operability Night sights, with integrated light source, on front and rear sights Mounts designed to accept light intensifier or infra-red sights Superior handling characteristics Ergonomically correct stock design for fast locking into the shoulder and quick target acquisition Ambidextrous design for left- and right-handed individuals All controls within easy reach Magazine "multipack" system and bolt hold open device for rapid magazine change Fast and easy handling required during combat situations... also providing for quicker proficiency in training Low weight factor High-grade synthetics are used for the butt, handguard, pistol grip and magazine Application of sophisticated weight-saving design concepts enhances mobility and reduces shooter fatigue Optimal layout Low sighting line mated to the correct stock angle Well designed pistol grip which places shooting hand in close alignment with bore axis A clear-cut decision for the Swiss Army In exhaustive comparitive trials, the outstanding performance and inherent attributes of the SIG 550/551 assault rifles clearly established their overall superiority. In consequence, the new infantry weapons of the Swiss Army bear the name of SIG. General issue to the troops begins in the 90's - hence the Swiss designation of Assault Rifle 90 (Stgw 90). Field-qualified for training and combat Dust, sand mudbath tests. Low temperature and winter trials under extreme conditions in the Swiss alps. Troop trials with live ammunition. Barrel erosion firings during development of the ammunition. All these trials and tests served to establish the overriding quality of the SIG assault rifles SG 550/551. They also earned this new weapon family the simple, meaningful qualification issued by Swiss Army of "field-grade". The SIG assault rifles of the SG 550/551 series are a weapon family. A maximum of common components and identical operation between weapons greatly simplifies training and logistics. New design methods and applied weight-saving concepts for both models eliminate the need for tools when field stripping or in the event of major takedowns. Consequently, the weapons can be rapidly stripped, cleaned and assembled for immediate readiness. Component interchangeability reduces downtime to an absolute minimum. The SG 550/551 series are extremely rugged weapons. They are designed to limit the ingress of mud, dust, dirt or sand. In extreme cases, the trooper can close the bolt manually. The gas valve has two settings to ensure reliable cycling, even under the most extreme conditions. Marksmanship qualification at 300m range, as is standard practice in Switzerland, or the training of sharpshooting special units calls for weapons with particularly high inherent accuracy. The SIG assault rifles SG 550/551 meet this, and related, requirements. Accurate marksmanship with these weapons is enhanced by a variety of factors, including: an overall sophisticated weapon concept, equal suitibility for left- and right-handers and exceptional inherent precision. The particular weapon layout of the SIG assault rifles SG 550/551 provides a low sighting line, resulting in a minimal exposure silhouette of the firer. The shooting hand (left or right) is located close to the bore axis. Also, the handguard has been extended well forward to allow unrestricted firing in any position. Single-shot, fully-automatic and 3-round burst modes permit the firepower to match the combat situation. The exceptionally low weight factor for an accurate assault rifle enhances mobility. This, in turn, increases firepower in assault situations, or the staying power of the individual trooper in other combat conditions. In close-quarter battle, the folding butt turns the SIG assault rifles SG 550/551 into handy and effective sidearms. The SG 550/551 fire 5.56mm caliber ammunition. Barrel rifling twist is matched to suit the ammunition. Standard, live ammunition is used to launch rifle grenades. The weapon cycles automatically and remains ready to fire at all times. Ammunition in 5.56mm (.223) caliber has excellent external and terminal ballistic properties. The lightweight plastic magazines can be clipped together to form multipacks. This feature, in combination with the automatic bolt hold-open catch, permits very fast magazine change. The SIG assault rifles SG 550/551 are equipped with night sights which are integrated in the diopter drum and the flip-up foresight. Additional accessories include a carrying sling, bayonet, cleaning kit and loading aid for rapid magazine filling. All SIG assault rifles SG 550/551 are equipped as standard with mounts to accept telescopic sights or night vision equipment (STANAG system).

SIG SG 550/551 Technical Specifications

Model	SG 550	SG 551
Caliber	.223	.223
Overall length	39.3 in	32.5 in
Length with butt folded	30.4 in	23.6 in
Barrel length	20.8 in	16.0 in
Rifling twist	7 in	7 in
Number of grooves	6	6
Sights	diopter	diopter
Sight Radius	21.2 in	18.3 in
Weight: with empty magazine and bipod	9.0 lbs.	7.7 lbs.
Trigger pull weight	6.6 lbs.	6.6 lbs.

Images and Information Courtesy of Schweizerische Industrie-Gesellschafte