Modern Firearms - SIG 540 / 542 / 543
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SIG SG-540 SG-542 SG-543 assault rifles (Switzerland)

 5.56mm SIG SG-540 assault rifle, with fixed butt and optional bipod
 5.56mm SIG SG-540 assault rifle, with fixed butt and optional bipod

 

5.56mm SIG-Manurhin SG-540 assault rifle as made in France under license, with side-folding butt
 5.56mm SIG-Manurhin SG-540 assault rifle as made in France under license, with side-folding butt

 

 7.62mm SIG SG-542 assault rifle, with fixed butt
 7.62mm SIG SG-542 assault rifle, with fixed butt

 

 5.56mm SIG SG-543 short assault rifle, with side-folding butt
 5.56mm SIG SG-543 short assault rifle, with side-folding butt

 

 

  SIGSG 540 SIGSG 542 SIGSG 543
Caliber 5.56x45mm(.223 Rem) 7.62x51mm(.308 Win) 5.56x45mm(.223 Rem)
Length 950mm 1000 mm 805 / 569 mm
Barrel length 460 mm 465 mm 300mm
Weight empty 3.26 kg 3.55 kg 3.0kg
Magazine capacity 20 or 30 rounds 20 or 30rounds 20 or30 rounds
Rate of fire 650-800rounds/min 650-800rounds/min 650-800rounds/min

 

The SIG SG-540 had been developed by the Swiss company SIG in the mid-1970s as a new,lightweight assault rifle, chambered in then-new small-caliber ammunition (.223 Rem / 5.56mm NATO). The SG-540 was licensed to the Manurhin of France and FAMAE of Chile, and had been temporarily used by FrenchArmy (who replaced it with FA MAS rifle in the early 1980s), Portuguese Army and Chilean army, and some other countries, mostly in South America and Africa. 7.62mm NATO version also had been developed, butfound no significant sales. The SG-540 itself had not been adopted by Swiss military, but it became the platform for further improvements,which lead to the SIG-550 / Stgw.90assault rifle. SG-540 currently is in production only by FAMAE company of Chile.

Early SIG prototypes, chambered in 5.56mm ammunition and known as SIG SG-530, were using some forms of roller locking, and thus, were too complicated and expensive to make. To made the rifle as cheap and reliable as possible, SIG designers selected the AK-47 style action,gas operated, with gas piston attached to the bolt carrier, and with rotating bolt with two massive lugs. The recoil spring is located around the gas piston rod, and the bolt carrier attached to the gaspiston rod by the removable charging handle. The gas port has gas regulator with two different open and one closed position (latter for firing rifle grenades). The receiver is made from stamped steel and hastwo major parts, upper and lower, which are connected by pushpins. The barrel is screwed into the upper receiver. The trigger unit has a safety/fire selector switch on the left side of the receiver, with 3 settings: safe, semi-auto, full-auto. If desired, additional modulecould be installed in the trigger mechanism to allow 3-rounds burstmode. Rear sights are drum-type (like those found on Heckler-Kochrifles). SG-540 has muzzle compensator/flash hider of NATO-standard diameter, so it is possible to launch rifle grenades from the muzzle.The SG-540 has integral folding bipods under the handguard, and can be issued with fixed plastic buttstock or with side-folding tubularmetallic buttstock.

The carbine version of the SG-540 is called SG-543 and has shorter barrel. SG-543 can't fire rifle grenades. 7.62mm version of SG-540 is known as SG-542 and visually differs mostly by rectangular magazine of greater depth. SG-542 is chambered for 7.62x51mm NATO ammunition. The civilian version of the SG-540 can fire only in-semi-auto and can be chambered also for .222 Remington cartridge. Other chamberings such as 7.62x39mm Russian (for SG 540) and.243Winchester (for SG 542) are possible but extremely rare.