Patent Publication Number: US-6986343-B2

Title: Mechanism for gas operated gun

Description:
This application is related to and claims priority from British application GB 0327683.9 filed Nov. 28, 2003. 
   FIELD OF THE INVENTION 
   This invention relates to an improved mechanism for a gas operated gun, by which is meant a gun of the type which fires a projectile by means of compressed gas. Guns of this kind are used in paintball games. Balls of paint are fired at other players to mark them. 
   DESCRIPTION OF THE PRIOR ART 
   Conventional paintball guns have a hollow bolt which, when the trigger is pulled to fire the gun, is moved from a rear to a forward position in the barrel, in the process selecting and moving forward the lowermost paintball in a magazine above the barrel. In the forward position of the bolt bores opening to its interior are exposed to compressed gas in a cylinder surrounding the bolt, causing the selected paintball to be expelled from the gun. When the trigger is released the bolt is moved back to its rear position, in which the bores are isolated from the cylinder. 
   A disadvantage of this otherwise simple arrangement is that more gas is used every time the gun is fired than is necessary to expel the selected paintball. Consequently the source of compressed gas, usually an air cylinder fitted to the gun housing, has to be replaced quite frequently, which is an expense and inconvenience. 
   U.S. Pat. No. 5,613,483 seeks to address this problem by attaching a spool valve to the rear of the bolt. A fill and a dump chamber are positioned in the gun housing behind the bolt. In the rear position of the bolt both chambers are filled with compressed gas, but when the bolt moves forward the spool valve isolates the chambers so that only the gas stored in the dump chamber escapes through the hollow bolt to fire the selected paint ball. A drawback of this gun is its complexity and relatively high manufacturing and maintenance costs. 
   SUMMARY OF THE INVENTION 
   A principal object of the present invention is to provide a simpler solution to the problem addressed by U.S. Pat. No. 5,613,483 allowing conventional paintball guns to have the advantages of the gun of that Patent as a result of a simple modification. 
   In accordance with the present invention there is provided a mechanism for a gas operated gun having a housing and a trigger, the mechanism comprising a hollow bolt slideably receiving a bolt guide fixed relative to the gun housing, the bolt being adapted to move to a forward position on the bolt guide when the trigger of the gun is pulled and to a rear position on the bolt guide when the trigger is released, the bolt having at least one radial bore at a position such that said bore is occluded by the bolt guide in the rear position of the bolt but not in the forward position of the bolt and a cylinder surrounding the bolt, the cylinder having a radial port communicating with a source of gas under pressure, characterised in that in the forward position of the bolt said port is occluded by the bolt to isolate the cylinder from said source such that only compressed gas stored in the cylinder is allowed to escape through said bore. 
   In a preferred embodiment of the invention the bolt has a circumferential recess dimensioned to communicate the interior of the cylinder with said source, the recess being in register with said port only when the bolt is in its rear position. 
   Said port is preferably located in a rearward position of the cylinder and communicates with said source via a passageway external to the cylinder and extending axially thereof. 
   Preferably means for displacing the bolt between its forward and rear positions surrounds the bolt guide behind said cylinder. 
   Said bore is preferably one of an array of radial bores circumferentially spaced around the bolt. 
   Said port may be a circumferential slot in a radial formation of the cylinder which extends into contact with the periphery of the bolt except when in register with said circumferential recess thereof. 
   The bolt guide may have axially spaced circumferential grooves in which respective O-ring seals are located, the positioning of the grooves being such that in the rear position of the bolt said bore or bores thereof is or are between said seals but in the forward position of the bolt said bore or bores is or are in advance of the foremost of said seals. 

   
     DESCRIPTION OF THE DRAWINGS 
     A preferred embodiment of the invention will now be described by way of non-limitative example with reference to the accompanying drawings, in which: 
       FIG. 1  illustrates part of the mechanism of a paintball gun showing the bolt in its forward or firing position, and 
       FIG. 2  illustrates the mechanism of  FIG. 1  showing the bolt in its rear or withdrawn position. 
   

   Several figures are provided to aid in the understanding of the present invention. The scope of the present invention is not limited to these figures. 
   DETAILED DESCRIPTION OF THE INVENTION 
   A paintball gun has a hollow, tubular bolt  10  which is slideable on a bolt guide  11  fixed cantilever fashion to the rear of the gun housing (not shown) by its head  12 . Surrounding the bolt and bolt guide is a mechanism  13  which serves to move the bolt  10  forward when the trigger (not shown) of the gun is pulled and rearward when the trigger is released. In the example illustrated this mechanism  13  works by placing a compressed gas canister (not shown) fitted to the gun selectively in communication with bores  14  and  15  whereby lands on the bolt will be driven in one direction or the other. This arrangement is conventional and so will not be further described, except to say that compressed gas actuation of the bolt may be replaced by an electronic system. 
   Forward of the mechanism  13  a cylinder  16  surrounds the bolt and bolt guide. The cylinder extends beyond the distal end of the bolt guide  11  so that in the forward position of the bolt ( FIG. 1 ) an array of circumferentially spaced radial bores  17  of the bolt exposes the interior of the bolt to the interior of the cylinder  16 . In the withdrawn position of the bolt ( FIG. 2 ) however the bores  17  are between O-ring seals  22  in axially spaced circumferential grooves  18  and  19  of the bolt guide  11  and therefore occluded from the cylinder  16 . 
   A port  20  at the rear of the cylinder  16  is in communication with the canister via a passageway  21  external to the cylinder and extending axially thereof. In accordance with a preferred embodiment of the invention the port  20  takes the form of a circumferential slot in a radial formation  22  at the rear of the cylinder dimensioned such that it is in contact with the periphery of the bolt  10  except when it is in register with a circumferential recess  23  in the bolt periphery. This occurs when the bolt  10  is in its withdrawn position ( FIG. 2 ) and the recess  23  has a length axially of the bolt such that it permits communication of the port  20  with the interior of the cylinder  16 . Therefore so long as the trigger of the gun is not pulled the cylinder  16  is charged with compressed gas which cannot escape to the interior of the bolt. When the trigger is pulled and the bolt  10  moves forward ( FIG. 1 ) the charge of compressed gas can escape from the cylinder  16  through the bores  17  to the interior of the bolt  10 , but meanwhile the port  20  is occluded by the periphery of the bolt because the recess  23  has moved forward. As is known per se the bolt  10  as it moves forward displaces in to the barrel of the gun the lowermost paintball in a magazine (not shown) mounted above the gun and the selected paintball is fired from the gun by the compressed gas escaping from the cylinder  16 . When the trigger is released and the bolt  10  is moved back the cylinder  16  is isolated from the interior of the bolt and is recharged with compressed gas as soon as the recess  23  comes back into register with the port  20 . 
   In a conventional paintball gun the cylinder  16  is permanently in communication with the gas canister so that gas will escape through the bolt  10  for as long as the latter remains in its forward, firing position. Such a gun can be readily modified to ensure that when the gun is fired only compressed gas stored in the cylinder  16  will escape.