SIG SG 550

Lore & Background

The SG 550 was developed to replace the Stgw 57 battle rifle, which used the 7.5×55mm GP 11 cartridge. In 1978, the Swiss armed forces sought a successor emphasizing modularity, reduced weight, and accuracy out to 300 meters. Two designs were considered: the W+F C42 and the SIG SG 541, based on the SG 540. In 1981, the experimental 6.45mm GP 80 cartridge was rejected in favor of the 5.6×45mm Gw Pat 90 round. The SG 541 was adopted in February 1983, redesignated SG 550 in October 1984, with production starting in 1986 and official service acceptance in 1990. Over 600,000 rifles have been delivered.

The rifle features a gas-actuated long-stroke piston system derived from the SG 540, with a manually adjustable gas valve for normal or fouled conditions. The rotary bolt has two locking lugs. The trigger mechanism includes an ambidextrous safety and fire selector with settings for safe, single, 3-round burst, and fully automatic fire. The side-folding skeletonized buttstock folds to the right, and a lightweight aluminum bipod folds into the handguard. The barrel is cold hammer-forged with a flash suppressor that can launch rifle grenades or mount a bayonet.

Accuracy testing at the manufacturer's underground 300 m range required a 50% windage and elevation dispersion of 11 cm (4.3 in) for any individual weapon, averaging 7 cm (2.8 in), using GP 90 ammunition. The sights are adjustable for windage and elevation, with a rear rotating diopter drum and hooded front post, offering settings for 100, 200, 300, and 400 meters.

Reader's Guide

The SIG SG 550's significance lies in its adoption as the standard Swiss service rifle, replacing the battle rifle era with a modern, modular assault rifle. Its design, co-developed with Beretta and based on the SG 540, set a benchmark for accuracy and reliability, with rigorous factory testing at 300 meters. The rifle's gas system and rotary bolt were proven designs, while the translucent polymer magazines and side-folding stock reflected contemporary ergonomic thinking. The SG 550 also saw a civilian sporting variant, the Swiss Arms PE 90, which became controversial in Canada due to reclassification as a prohibited weapon in 2014 and again in 2020, following the Nova Scotia attacks. The 2014 reclassification was overturned in 2015 after legal challenges, but the 2020 order reinstated prohibition. The rifle's legacy includes over 600,000 units delivered to the Swiss military, with production now ceased, and its influence on subsequent SIG designs.

Did You Know?

• The SG 550 was originally designated SG 541 before being renamed in October 1984.
• The rifle's 3-round burst and fully automatic settings can be disabled by a rotating safety guard.
• The Swiss military designation for the SG 550 is Stgw 90.
• The SG 550's accuracy is tested at a 300 m underground range using a circular error probable method.