SIG SG 540

Lore & Background

Work on a new generation of lightweight rifle using the intermediate 5.56mm round began at SIG in the 1960s, resulting in the SG 530-1 design with a gas-assisted roller-delayed blowback mechanism that proved too complicated and expensive. In 1969, SIG adopted a simpler piston-operated rotating bolt locking mechanism derived from the Soviet AK-47. This combination proved successful, and the rifle entered production as a family including the base SG 540, the 7.62mm SG 542 battle rifle, and the 5.56mm SG 543 carbine. Due to Swiss federal restrictions on firearms exportation, manufacturing was carried out at the Manurhin facility in Mulhouse, France.

The SG 540 is an air-cooled, gas-operated, selective fire assault rifle firing from a closed bolt. It uses a long-stroke piston with an adjustable gas regulator (settings for rifle grenades, normal, and extreme conditions). The rotating bolt has two locking lugs. The fire control selector offers safe, semi-automatic, 3-round burst, and fully automatic modes. The rifle is fed from 20- or 30-round magazines, with a bolt hold-open feature. It has a flash suppressor for grenades and bayonet, adjustable iron sights (100–500 m), and can mount optics. The stock is either fixed polymer or side-folding metal skeleton; a folding aluminium bipod is standard. The weapon uses cost-saving pressed and stamped steel components.

Reader's Guide

The SG 540 series entered service with armed forces in Africa, Asia, and South America, as well as numerous law enforcement and security services. In 1988, Portuguese manufacturer INDEP purchased rights to license-build the SG 543 carbine. Currently, the SG 540, SG 542, and SG 543 are manufactured in Chile under license by FAMAE for the Chilean Armed Forces. The SG 540 served as the basis for the SG 541 prototype, which later became the SG 550 (Stgw 90) adopted by the Swiss Armed Forces. The design's robust piston-operated action, derived from the AK-47, contributed to its reliability and export success. The SG 542 variant, chambered in 7.62×51mm, was adopted by several armies, including Ecuador. The SG 543 carbine, with a shorter barrel and no bipod, was used by Portuguese commandos until 2019. Semi-automatic civilian variants were manufactured by Manurhin in .222 Remington and .243 Winchester to comply with European regulations on military cartridges.

Did You Know?

• The SG 540's operating mechanism is derived from the Soviet AK-47's piston-operated rotating bolt.
• Due to Swiss export restrictions, initial production was carried out at Manurhin in France.
• The SG 543 carbine lacks the integral bipod and cannot fire rifle grenades.
• Civilian semi-automatic variants were chambered in .222 Remington and .243 Winchester to avoid restrictions on military cartridges.