1. In a machine gun with a barrel having a bore of predetermined diameter with a forward muzzle end and a rearward receiver end having a receiver including mechanism which operates said gun that improvement which consists of: gas actuating and evacuation means responsive to gas pressure generated by the discharge of a round in said barrel for operating said receiver mechanism and collecting exhausted gas for discharge at a location at least as far forward as adjacent the nuzzle end of said barrel, said means comprising barrel gas port means including a gas port in said bore located generally in the mid-portion of said barrel, a gas cylinder mounted on said barrel, said cylinder having a forwardly located gas inlEt port communicating with said barrel gas port for supplying to said cylinder gas under pressure from said barrel and forwardly and rearwardly located gas outlet ports a piston within said cylinder movable between a forward position in communication with said cylinder gas inlet port to a rearward position in communication with said rearward gas outlet port gas evacuation tube means extending forwardly externally of said cylinder generally parallel thereto and to said barrel from said rearwardly located gas outlet port to a location at least as far forward as adjacent the muzzle end of said barrel said gas evacuation tube means communicating with said forwardly and rearwardly located cylinder gas outlet ports for discharging said exhausted gas in a forward direction at least as far forward as adjacent the muzzle end of said barrel.

1. In a machine gun with a barrel having a bore of predetermined diameter with a forward muzzle end and a rearward receiver end having a receiver including mechanism which operates said gun that improvement which consists of: gas actuating and evacuation means responsive to gas pressure generated by the discharge of a round in said barrel for operating said receiver mechanism and collecting exhausted gas for discharge at a location at least as far forward as adjacent the nuzzle end of said barrel, said means comprising barrel gas port means including a gas port in said bore located generally in the mid-portion of said barrel, a gas cylinder mounted on said barrel, said cylinder having a forwardly located gas inlEt port communicating with said barrel gas port for supplying to said cylinder gas under pressure from said barrel and forwardly and rearwardly located gas outlet ports a piston within said cylinder movable between a forward position in communication with said cylinder gas inlet port to a rearward position in communication with said rearward gas outlet port gas evacuation tube means extending forwardly externally of said cylinder generally parallel thereto and to said barrel from said rearwardly located gas outlet port to a location at least as far forward as adjacent the muzzle end of said barrel said gas evacuation tube means communicating with said forwardly and rearwardly located cylinder gas outlet ports for discharging said exhausted gas in a forward direction at least as far forward as adjacent the muzzle end of said barrel.

2. In a machine gun with a barrel having a bore of predetermined diameter with a forward muzzle end and a rearward receiver end having a receiver including mechanism which operates said gun that improvement which consists of: gas actuating and evacuation means responsive to gas pressure generated by the discharge of a round in said barrel for operating said receiver mechanism and collecting exhausted gas for discharge in a forward direction, said means comprising: barrel gas port means including a gas port in said bore located generally in the mid-portion of said barrel a gas cylinder mounted on said barrel, said cylinder having a forwardly located gas inlet port communicating with said barrel gas port for supplying to said cylinder gas under pressure from said barrel and a rearwardly located gas outlet port a piston within said cylinder movable between a forward position in communication with said cylinder gas inlet port to a rearward position in communication with said rearward gas outlet port an operating tube extending between the rear end of said cylinder and said receiver an actuating rod in said tube, said actuating rod extending through the rear wall of said cylinder for actuation by said piston for movement of said rod in said tube independently of said piston to operate said receiver mechanism rod sealing means mounted on said actuating rod and cooperating with said operating tube for preventing exhausted gas from leaking into said receiver and for controlling deposit of said combustion residues within said operating tube and gas evacuation means extending from said rearwardly located cylinder gas outlet port for discharging exhausted gas in a forward direction.