USAS-12 shotgun was developed in South Korea by Daewoo Precision Industries somewhere in the 1980's. USAS-12 was intended as a special purpose,  military or special operations close combat weapon with extreme firepower. USAS-12 is feed from large capacity box (10 rounds) and drum magazines (20 rounds). USAS-12 has a post type, hooded front sight at the top of the gas chamber and an adjustable rear sight built into the carrying handle, similar to one found on M16 assault rifles. USAS-12 is very bulky and heavy, but the large mass greatly improves the recoil control, especially in full automatic mode.  
USAS-12 Automatic Shotgun
       
  USAS-12 is a gas operated, selective fire weapon. It uses a gas system located above the barrel, with more or less conventional rotating bolt locking. The interesting feature, probably borrowed from Atchisson designs, is the long bolt overtravel, which results in relatively low peak recoil and low rate of fire, which is essential for weapon firing powerful 12 gauge shells. USAS-12 is an ambidextrous weapon, having two ejection ports on each side of the receiver, and two slots on the forearm for cocking handle. The ejector on the bolt and the cocking handle could be easily set to operate either side of the gun, depending on the present shooter needs and preferences.

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

 
USAS-12 unloaded with box of shells
       
  GAME DATA: USAS-12

The USAS-12 is as deadly as it is bulky and heavy. 10 rounds of 12 gauge buckshots in few seconds will do great damage at close range and in closed spaces.
Used by heavy Prometheus troops.

   
Name: USAS-12  
Slot: 3, shotguns  
Caliber: 12 gauge  
Capacity: 10 rounds  
Firemodes: Semi- and full-auto  
Accuracy: Poor  
   
   

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