The SIG SG-55x assault rifles have been developed by Swiss company SIG as a competitor for Swiss Army assault rifle contest in 1979 - 1980. SG-550 had been derived from previous model SIG 540 and SIG 541, and was adopted as a Stgw.90 assault rifle in 1983, but due to financial reasons production began only in 1986. Currently, the Stgw.90 is a standard Swiss service rifle and also offered for export. "Carbine" version and subcompact assault rifle versions available in the form of SG-551 and SG-552 "Commando". The carbine version of the SG-550 is called SG-551 and has shorter barrel. Even more compact rifle, SG-552, is similar to SG-551 except that it has shorter handguard and barrel.
SIG SG-551 Carbine
SIG SG-551 Tactical Carbine with 2X night vision scope
       
 
SIG SG-551-P Sniper Carbine with 4X sniper scope as standard
SIG magazines can be attached to each other
  SG-55x featured AK47 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, above the barrel, and the bolt carrier attached to the gas piston rod by the mean of 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 has two 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. All SG-55x rifles have a side-folding, skeletonized polymer buttstock.

-(Shortened and/or modified version of the article at world.guns.ru)

       
  GAME DATA: SG-551

The SG-551 Carbine is a good assault rifle. It has only 20 round magazines, but with great accuracy it works wonders even at long ranges.

   
Name: SG-551 Carbine  
Slot: 5, rifles  
Caliber: .223 Remington  
Capacity: 20 rounds  
Firemodes: Full-, semi-auto and 3 round burst  
Accuracy: Good  
   
   
  GAME DATA: SG-551-P

The SG-551-P is a sniper variant of the SG-551 rifle. With a match grade barrel and a 4X scope it's an accurate weapon, but with the 5.56x45mm ammo and a short barrel it works best at shot/medium ranges like in an urban enviroment. Standard sniper rifle of the Prometheus faction.

   
Name: SG-551-P Sniper Carbine  
Slot: 5, rifles  
Caliber: .223 Remington  
Capacity: 20 rounds  
Firemodes: Full-, semi-auto and 3 round burst  
Accuracy: Very Good  
Other: 4X sniper scope  
   
   
  GAME DATA: SG-551

The SG-551 Tactical Carbine sports a 2x night vision scope to give it more accurasy. This weapon is the standard workhorse of the Prometheus faction.

   
Name: SG-551 Tactical Carbine  
Slot: 5, rifles  
Caliber: .223 Remington  
Capacity: 20 rounds  
Firemodes: Full-, semi-auto and 3 round burst  
Accuracy: Good  
Other: 2X night vision scope  
   
   
   

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