Concentric cylinder gas-operated automatic firearm

Abstract

A fixed-barrel, gas-operated firearm having its barrel concentrically mounted within a pressure tube enclosing substantially all of the moving parts of the firearm's action. A gas cup reciprocates under the influence of propellant gas pressure when the firearm is fired, driving slide members that link the pressure cup to the firearm's bolt rearward within the pressure tube, unlocking the breech, rotating and retracting the bolt, discharging the spent cartridge casing and then advancing the bolt to chamber a new cartridge.

1 . A firearm comprising:
 a barrel having a bore extending therethrough and defining a central lengthwise barrel axis through the bore, and a chamber on one end configured to receive a loaded round of ammunition;   a pressure tube surrounding the barrel;   a breech block affixed within the pressure tube, a breech end of the barrel is secured to the breech block;   a muzzle cap secured around a forward end of the barrel; and   an annular enclosure formed between an interior surface of the pressure tube and an outer surface of the barrel between the breech block and the muzzle cap.   
     
     
         2 . The firearm of  claim 1 , further comprising a gas cup having an outer rim for sliding in proximity with the interior surface of the pressure tube, and an inner opening for sliding in proximity with the outer surface of the barrel. 
     
     
         3 . The firearm of  claim 2 , further comprising a pair of slide rails extending from the gas cup through an internal portion of the pressure tube and alongside a portion of the breech block. 
     
     
         4 . The firearm of  claim 2 , further comprising a spring positioned about the barrel configured to biases the gas cup toward a muzzle end of the firearm. 
     
     
         5 . The firearm of  claim 3 , further comprising guide channels extending lengthwise along the inner surface of the pressure tube configured to receive and guide the slide rails of the gas cup.