Abstract:
A gas porting structure for an autoloading gun, wherein the structure consists of an insert fitting within a slot cut laterally thru the gun barrel and wherein one or more slot like gas ports are formed thru the insert in a longitudinal direction generally axial of the barrel.

Description:
BACKGROUND OF THE INVENTION 
   1. Field 
   This invention concerns unique structure for the gas exit port in the barrel of autoloading shotguns or the like, which port exits the high pressure firing gas into the gas cylinder of the spent shell ejection system. Such gun structure is shown and described in detail in U.S. Pat. Nos. 4,693,170; 4,487,103; 4,553,469 4,654,993; and 4,893,547, the disclosures of which are hereby incorporated herein by reference in their entireties. 
   2. Prior Art 
   The above patents show the conventional gas porting structure which, for example, is designated 68 in the aforesaid U.S. Pat. No. 4,693,170 patent. Such porting is simply a slot or holes drilled thru the barrel from the outside in which leaves burs or sharp edges on the inside of the barrel. These burs and edges will naturally collect shell debris from repeated firings and restrict the proper flow of gases and also clog the gas cylinder of the ejection system and other components of the gun. 
   SUMMARY OF THE INVENTION 
   The present invention eliminates such burrs and sharp edges and debris collection by means of providing a gas porting structure comprising a relatively large lateral cut out in the barrel, and porting insert means having an overall exterior configuration conforming substantially to the overall exterior configuration of said cut out and adapted to fit into said cut out with substantial precision, wherein at least one gas port is formed laterally thru said insert means from its exterior surface thru its interior surface, and wherein the interior edge portions of said port are smooth and radiused. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be understood further from the following description and drawings wherein the figures are not drawn to scale or proportion and are intended to visually depict the concepts of the present invention, and wherein: 
       FIG. 1  is a cross sectional view of the gun barrel portion and adjacent gas ejection cylinder construction as shown in  FIG. 5  of the aforesaid U.S. Pat. No. 4,693,170 wherein the construction of the gas port 68 of the patent has been modified by means of an insert in accordance with the present invention and wherein the cross-section of the insert is taken along line  6 — 6  in  FIG. 4 , i.e., longitudinally thru one of the gas ports thru the insert, with other portions of the insert shown in dotted outline; 
       FIG. 2  is a side elevation view of the said barrel portion showing the approximate preferred depth of the cut out for the porting insert; 
       FIG. 3  is a top view of the said barrel portion of  FIG. 2 ; 
       FIG. 4  is a view as in  FIG. 3  with the porting insert in place in said cut out; 
       FIG. 5  is a cross-sectional view of the porting insert taken along line  5 — 5  in  FIG. 4  with the port or aperture separators or lands isolated; 
       FIG. 6  is a cross-sectional view of said insert taken along line  6 — 6  in  FIG. 4  with other portions of the insert shown in dotted outline; 
       FIG. 7  is a view taken along line  7 — 7  of  FIG. 1  showing portions of the gas collection chamber  67  and adjacent structure; 
       FIG. 8  is a view as in  FIG. 5  with the claimed radii denoted; and 
       FIG. 9  is a partially schematic and cross-sectioned representation of a bolt carrier assembly, shotgun shell and shell extractor means. 
   

   DETAILED DESCRIPTION 
   Referring to the drawings and with particular reference to the claims herein and to the aforesaid patent U.S. Pat. No. 4,693,170, the present invention comprises a cut out generally designated  10  in the barrel  40  entering into the barrel bore  29  into which cut out a gas porting insert generally designated  12  is positioned at close dimensional tolerances, e.g., within about one to about 10 thousandths of an inch. This insert is formed with a lateral dimension “LD” and longitudinal or axial dimension “AD” and a gas porting means having one or more ports  14  wherein, for example for a 12 gauge shotgun, the gas flow area of each port—cross-hatched area—should be such that the total flow or cross-sectional area of all ports combined, preferably is from about 0.05 in 2  to about 0.12 in 2 . The insert structure shown, with four ports, is highly preferred as it affords an adequate gas flow rate while providing good longitudinal or axial, land ( 16 ) area on which firing debris such as shell wadding can readily slide on its way out of the barrel. Also, all of the ports are preferably formed along parallel axes a 1 , a 2 , a 3  and a 4 . 
   In further detail and with particular reference to the present claims and amended drawings herein, the present gas porting structure is designed for an autoloading firearm having a cylindrical barrel  40  having an outer cylindrical surface portion  41  and a cylindrical inner (bore) surface  42  and a discharge gas cylinder  69  and piston  44  in gas flow communication with gas porting means  11  provided thru the wall of said barrel and communicating directly with the bore  29  thereof. Piston  44  is affixed to a bolt carrier assembly  148  having a shell extractor means  159 , whereby flow of discharge gas into said cylinder  60  will force said piston  44  rearwardly to retract the bolt carrier assembly  148 , actuate the shell extractor means  159  and eject a shell  244 . The porting means generally designated  11  comprises a lateral cut out  10  completely thru a wall section of said barrel and gas porting insert means  12  positioned in said cut out, wherein said insert means has an outer surface  13  and an inner surface  15  formed on concentric radii  17  and  19  respectively. These radii  17  and  19  are the same (as close as possible) as outer radius  21  and bore radius  23  respectively of barrel  40 . Insert means  12  has the same length, thickness and width as said cut out and is fitted into said cut out with substantial precision whereby said inner surface  15  becomes a section of barrel bore  29 , wherein at least one gas port  14  is formed thru said insert means and wherein edge portions of said inner surface which outline said at least one gas port are curved such as to eliminate any sharp edge portions on which firing debris could be snagged. 
   The present method of providing a firearm barrel is unique as evident from the specification and drawings herein and as evidenced by the state of the art. 
   In the manufacture of the present insert the inside edges  18  of the ports, both of the sides  20  and ends  22  of the ports, are radiused and deburred by any suitable means such as machining, sand blasting or grinding or the like. This deburring is readily done on the present filly accessible insert but would be very difficult, expensive and impractical to perform on the barrels of the prior art. The radiused of the port edges, particularly of the end edges, should be large enough to offer little if any resistance to the flow of firing debris thru the barrel. 
   Referring to present FIG.  1  and to FIG. 5 of the aforesaid U.S. Pat. No. 4,693,170, the front of the gas operated antirecoil, shell ejection cylinder and the adjacent portions of the present modified barrel are shown and comprises gas cylinder and front sight  28 , base  56 , pin slots  24  in  56  gas hole  70 ,  71 , gas cylinder  69 , gas piston  44 , piston rod  46 , guide rod  43 , action spring  45 , barrel  40 , pins  66 , pin slots  26  in  40 , gas collection chamber  67  and the present cut out  10  and insert  12 . It is noted that the total flow area thru chamber  67  should approximate the total flow area of ports  14 . 
   The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications will be effected with the spirit and scope of the invention.