SG 540

The SG 540 is a 5.56×45mm NATO assault rifle developed in the early 1970s by Schweizerische Industrie Gesellschaft (SIG) as a private venture primarily for export markets and as a potential replacement for the 7.5×55mm Swiss SG 510. 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 which employed a gas-assisted roller-delayed blowback operating mechanism. This proved complicated and expensive, leading SIG in 1969 to adopt a design using a piston-operated rotating bolt locking mechanism. This combination proved successful, and the rifle entered production between 1973 and 1974 as a family consisting of the base 5.56mm 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. In 1988, the Portuguese defense manufacturer INDEP purchased rights to license build the SG 543 carbine. The SG 540 series is currently manufactured under license by FAMAE in Chile.

The SG 540 is an air-cooled, gas-operated, selective fire assault rifle that fires from a closed bolt position. It uses a long-stroke piston-driven action, with the recoil spring wrapped around the piston rod, and an adjustable gas regulator with three settings for normal, extreme conditions, or rifle grenade launch. The firearm is locked by a rotating bolt featuring two steel locking lugs, actuated by a control cam in the bolt carrier. The rifle is hammer-fired and includes a combined fire control selector and safety mechanism with settings for safe, semi-automatic, 3-round burst, and fully automatic fire. It is fed from 20 or 30-round staggered box magazines, with a hold-open device engaging the bolt catch after the last round. A bolt release button is located on the left side. The barrel is fitted with a flash suppressor compatible with 22 mm spigot-type rifle grenades and a bayonet. Iron sights consist of a hooded foresight and a rear rotating diopter drum with settings for 100, 200, 300, and 500 m. The receiver top surface can accept optics adapters. The rifle is equipped with either a fixed or a side-folding metal stock and typically includes a folding lightweight aluminum bipod. The stock, pistol grip, and handguard are made of polymers, and the weapon incorporates pressed and stamped steel components.

The SG 540 family includes:

• the base 5.56mm SG 540,
• the 7.62mm SG 542 battle rifle,
• and the 5.56mm SG 543 carbine.

Both 5.56mm variants were designed for 5.56×45mm M193 ammunition, while the SG 542 is chambered for 7.62×51mm NATO. The SG 542 adopts the more powerful 7.62mm cartridge and features modified sights with an additional 600 m setting. The SG 543 is a shortened SG 540 with a 300 mm barrel, shorter gas system, different handguard and sights with settings up to 400 m; it lacks the integral bipod and cannot fire rifle grenades. The SG 540 also served as the basis for the SG 541 prototype, which became the SG 550. Two semi-automatic civilian variants were manufactured by MANURHIN: the SIG Manurhin F.S.A. in .222 Remington and the SIG Manurhin C.S.A. in .243 Winchester, available with 30 or 5-round magazines and fixed or folding stocks. FAMAE exported semi-automatic SG 540 (.223) and SG 542 (.308) rifles, along with restricted SG 543 (.223) and 9 mm SAF carbines to Canadian civilians.

The SG 540 series has entered service with the armed forces of several countries in Africa, Asia, and South America, as well as numerous law enforcement and security services. Produced under license by Manurhin, the rifle saw temporary, limited service with the French army, French Foreign Legion, Fusiliers marins, RAID, and National Police Intervention Groups during the late 1970s before being replaced by the FAMAS. The SG543-1 was used by Portuguese army Commandos and Special Operations Troops Centre from the 1980s until 2019, when it was replaced by the FN SCAR. In Chile, the rifle is currently being replaced with the IWI Galil ACE.

Current users include Argentina, Bolivia, Burkina Faso, Cameroon, Canada (Lethbridge Police Service), Central African Republic, Chad, Chile, Côte d'Ivoire, Democratic Republic of the Congo, Djibouti, Ecuador, Eswatini, Gabon, Lebanon, Mauritius, Nicaragua, Nigeria, Oman, Paraguay, Senegal, Seychelles, Syrian Opposition, and Togo. Former users include France and Portugal.