Abstract:
A special stock assembly for break barrel air guns includes a bullpup stock assembly which allows a break barrel air gun to normally break without requiring any modification to the cylinder, or cocking mechanism. The invention can include the mechanical components of a break barrel air rifle as part of an original manufacture with the gun by moving the trigger assembly forward, or as an after market retrofit to an existing gun, in which case a cable linkage is provided between the in situ OEM trigger assembly and an additional trigger pull provided with the bullpup stock assembly. The cable linkage connects a forward trigger assembly to the OEM trigger and can have a 1:1 ratio of trigger movement between the forward trigger pull and the OEM trigger, or another ratio as determined by the linkage elements. The forward trigger assembly can be purely mechanical, or incorporate a servo and/or solenoid with a power source such as a battery to augment trigger pull by a trigger finger.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. Non-provisional application Ser. No. 14/446,335 having a filing date of Jul. 30, 2014 titled “A Bullpup Stock Assembly with Break Barrel Gun” which claims the benefit of U.S. Provisional Application No. 61/859,801 filed Jul. 30, 2013 
    
    
     FIELD 
     The present invention relates generally to a bullpup stock for break barrel air guns 
     BACKGROUND 
     In a “bullpup” type stock, the action of the gun is behind the trigger in front of a short buttstock. This results in a shorter overall firearm length and improves maneuverability. 
     Break barrel air guns contain either a spring-piston or a gas-spring in which a cylinder is pressurized by a cocking mechanism wherein the gun barrel is hinged midway between the barrel and cylinder assembly, and whereby the barrel operates as a cocking lever to compress the piston. Cocking of a break barrel rifle is often accomplished by bracing the butt of the stock against the thigh with the barrel pointing up and at an angle whereby the end of the barrel can be grasped and pulled downwardly causing a levered cocking mechanism to compress the piston. Being thus pressurized, the barrel is then raised and locked in normal inline position. Irrespective of the spring type employed, break barrel air guns are known for their accuracy and can propel a 177 cal pellet up to 1300 ft/sec. Because of the relatively simple mechanical pressurization means, these air guns have a high power to weight ratio and provide long and dependable service. Despite the many advantages of the break barrel air gun, cocking the gun can be awkward. Furthermore, the amount of force required for the cocking stroke is significant, with some persons experiencing fatigue after repeated cocking. Another issue is that the form of the cocking mechanism in most break barrel air guns has tended to promote homogeneity in stock design. It would be desirable therefore to provide a special bullpup stock assembly that among its many features, assists a user&#39;s body mechanics by providing a projecting fulcrum at or adjacent to the pivot point of the cocking mechanism while still permitting the gun to cock (break) normally. 
     SUMMARY 
     The present invention seeks to address, among other problems, the difficulty of cocking break barrel air guns by providing a bullpup stock assembly which allows a break barrel air gun to normally break without requiring any modification to the cylinder, or cocking mechanism. The invention can include the mechanical components of a break barrel air rifle as part of an original manufacture with the gun by moving the trigger assembly forward, or as an after market retrofit to an existing gun, in which case a cable linkage is provided between the in situ OEM trigger assembly and an additional trigger pull provided with the bullpup stock assembly. The cable linkage connects a forward trigger assembly to the OEM trigger and can have a 1:1 ratio of trigger movement between the forward trigger pull and the OEM trigger, or another ratio as determined by the linkage elements. The forward trigger assembly can be purely mechanical, or incorporate a servo and/or solenoid with a power source such as a battery to augment trigger pull by a trigger finger. 
     In one implementation, the present invention provides the comfort and maneuverability of a bullpup stock assembly to a break barrel air gun. Advantageously, the instant invention provides a projecting fulcrum in the form of a grip which can be placed against the torso; preferably just below the sternum, whereby the rifle is then easily cocked by keeping each arm substantially level with the other, as opposed to past cocking methods requiring awkward body mechanics. 
     In another implementation, the present invention provides for a specially shaped buttstock that partially rests on the shoulder of the shooter, (1) decreasing the length between the eye and the sight or scope, and (2) preventing the shooter&#39;s arms from over extending. The specially shaped buttstock also allows for hands-free resting of the gun in a downwardly pointing position. 
     In whatever aspect, at least one objective of the present invention is to improve both the useability and appearance of a break barrel gun. Advantageously, the stock of the present invention permits a one piece cocking linkage configuration as opposed to conventional two piece linkages that include a pair of connected levers. The one-piece configuration relieves the effort required to cock the rifle at a final stage of the cocking stroke. The instant invention provides hand grip interchangeability. 
     Other possible uses and combinations of disclosed aspects and features of the instant invention will suggest themselves to those having skill in the art, and benefit of this disclosure. 
     The foregoing and other objects, features, and advantages of the invention will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an assembly view of a typical spring piston break barrel air rifle; 
         FIG. 2  shows a side perspective view of a preferred embodiment according to the present invention including a break barrel air gun (AG), stock assembly  200  and buttstock  290 ; 
         FIG. 3  shows a top perspective view of a preferred embodiment according to the present invention having an angularly offset stock, and wherein a stock  200  is shown having a cavity  240  shaped and sized to fit to the mechanical components of an air rifle; 
         FIG. 4  shows a bottom perspective view of a preferred embodiment according to the present invention opposite that of ( FIG. 3 ) wherein slot  210  permits the passing through of certain mechanical components of an air rifle; 
         FIG. 5  shows a side perspective view of a preferred embodiment according to the present invention; 
         FIG. 6  shows a side perspective view of a preferred embodiment according to the present invention opposite that of ( FIG. 5 ); 
         FIG. 7  shows an end view of a preferred embodiment according to the present invention; 
         FIG. 8  shows an end view of a preferred embodiment according to the present invention opposite that of ( FIG. 7 ); 
         FIG. 9  is an detail view showing the barrel pivoted downwardly; 
         FIG. 10  is detail view taken from a side opposite that shown in ( FIG. 9 ); 
         FIG. 11 a    is a detail view of a conventional cocking linkage which includes a pair of levers that are connected; 
         FIG. 11 b    is a detail view of a conventional cocking linkage which includes a pair of levers that are connected, and wherein guide roller (GR) is constrained by an inner portion of a stock, omitted in this view, to move in a motion generally parallel to the air cylinder  130 ; 
         FIG. 12  is a detail view of a one piece cocking lever for use with a preferred embodiment according to the present invention; 
         FIG. 13  is a detail view of an end of a stock according to a preferred embodiment; 
         FIG. 14  is a perspective view showing the orientation of mechanical components of a typical break barrel air rifle and a stock according to a preferred embodiment; 
         FIGS. 15-17  show respectively, the steps for cocking a preferred embodiment according to the present invention, that includes gripping the ends of the stock and barrel and placing the grip  220  against the chest, using the grip as a fulcrum, breaking the barrel in a direction that is generally toward the body, and continuing the breaking motion and lowering the arms to greater advantage. 
         FIG. 18  shows a buttstock of one embodiment placed over the shoulders for hands-free support of the rifle; 
         FIG. 19  is a perspective view illustrating a carrying method corresponding to a preferred embodiment of the present invention; 
         FIG. 20  is a perspective view illustrating an embodiment in ready position; 
         FIG. 21  is a detail view illustrating an offset interchangeable pistol grip and trigger assembly to one side of slot  210 ; 
         FIG. 22   as  a partial view of a stock AR15 lower receiver with modified disengageable trigger guard; 
         FIG. 22 b    in a schematic diagram shows the configuration of a augmented trigger pull assembly; 
     
    
    
     In the following detailed description, like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference Listing 
     
         
           100  barrel 
           110  breech 
           112  breech lock 
           120  break 
           130  air cylinder 
           140  cocking mechanism 
           141  cocking linkage 
           150  OEM trigger 
           200  stock assembly 
           210  slot 
           220  grip 
           230  stub 
           240  recess 
           250  trigger 
           260  cable 
           280  attachment point 
           290  buttstock 
           300  drawbar 
           305  drawbar linkage 
           306  trigger guard 
           307  trigger guard slot 
           308  auxiliary trigger 
           310  servo 
           320  potentiometer 
           322  battery 
           330  motor 
           340  pulley 
       
    
     DEFINITIONS 
     In the following description, the term “air gun” refers generally to any air gun with single or multiple stroke cocking means, and more particularly to break barrel type air rifles. The term “cocking mechanism” refers to those portions of the air gun associated with cocking or pressurization functions and include at least the air cylinder, pivot pins, cocking levers, and the piston; whether spring or gas actuated. The term “conventional stock” refers to gun stocks where the action is forward of the trigger assembly, and the butt of the stock is braced against the shoulder. The term “body mechanics” refers to various positions assumed for physically cocking, carrying, and aiming the gun. Unless otherwise explained, any terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The singular terms “a,” “an,” and “the” include plural referents unless the context clearly indicates otherwise. Similarly, the word “or” is intended to include “and” unless the context clearly indicates otherwise. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of this disclosure, suitable methods and materials are described below. The term “comprises” means “includes.” Publications, patent applications, patents, and other references mentioned herein, if any, are incorporated by reference in their entirety for all purposes. In case of conflict, the present specification, including explanations of terms, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. 
     Referring generally to  FIGS. 1-21 , in combination with a break barrel air gun AG possessing at least a barrel  100 , a breech  110 , an air cylinder  130 , cocking mechanism  140  and cocking linkage  141 , a special bullpup stock assembly  200  includes a formed recess  240  shaped and sized to accept certain mechanical components of a break barrel rifle and OEM rear trigger assembly if one is present. A slot  210  is formed at the bottom of stock assembly for the passing through of portions of the cocking linkage mechanism when the air gun is cocked. Hand grip  220  is either unitary or interchangeable with the remainder of the stock and provides a fulcrum for the cocking mechanism whereby improved leverage is obtained when cocking the rifle. Trigger  250  is connected by cable  260  or other linkage as will be appreciated by those having skill in the art and benefit of this disclosure to OEM trigger  150 , or, in case of new manufacture, stock  200  is shaped and sized to accommodate an OEM trigger with direct linkage to the action. The stock assembly of the preferred embodiment has a buttstock  290  shaped and sized to rest atop a person&#39;s shoulder which is unitary with stock  200  or interchangeable with other buttstocks by means of threaded connectors, posts, or the like. 
     Referring to  FIG. 2 , an embodiment is shown wherein the barrel is in cocking (broken) position. Dotted lines represent the cable linkage between the OEM trigger  150  and the forward trigger  250 . It should be noted that the particular triggers shown are not to be considered limiting. The connection of the cable to the OEM trigger can be direct or via other trigger linking elements such as a cam or lever which is ultimately connected to the OEM trigger assembly. 
     Referring generally to  FIGS. 3-8 , stock  200  is shown in various profile views with buttstock  290  removed. Although in the particular embodiment depicted, buttstock  290  is connected to the stock via threaded bolt, the buttstock can be unitary with the remainder of the stock or other connections as will suggest themselves to those having skill in the art and benefit of this disclosure may be employed without departing from the claimed invention. Accordingly, any connecting or fastening means between the buttstock and remainder of the stock including mating connections with dovetail shapes or other shapes, and/or pegs or screws can be employed without departing from the spirit and scope of the disclosed invention. 
     Referring to  FIGS. 4, 9 and 10 , slot  210  is formed to permit the passing through of certain portions of the air rifle, namely a section of the breech end of the barrel, and cocking linkages  141 . 
     Referring specifically to  FIG. 11 a   , a cylinder and cocking mechanism of a typical break barrel air gun is depicted. Unless a stock is coupled to air cylinder  130  thereby constraining guide roller (GR) within an inner channel or groove of the stock (not shown), linkage  141  projects from the cylinder and barrel when in the barrel is drawn into cocking position.  FIG. 11 b    shows the position of the cocking linkage when a stock—omitted here for clarity, is fitted to the air cylinder. The two part configuration ( FIGS. 11 a , 11 b   ) of conventional air rifle cocking linkages, while adequate to pressurize the cylinder, is in part, a design concession to emulate the appearance of a non-air rifle, and is not an optimal configuration for ease of use. Generally, the foregoing configuration, while providing for easier initial breaking, is followed by more difficulty when the barrel is past the 90 degree position due to the direction of force applied to the shorter lever. Accordingly, in a preferred embodiment, as depicted in  FIG. 12 , a one-piece cocking linkage is provided so that superior mechanical advantage is obtained when the barrel and stock are drawn together in the final stage of the cocking stroke. This is important because the configuration of disclosed embodiments and especially the grip as a fulcrum already provides for easier initial breaking. The one-piece cocking linkage further reduces the total amount of effort required to cock the break barrel rifle. 
     Moving to  FIGS. 13 and 14 , a detail view shows an OEM trigger projecting from the rear of stock  200 . Also shown is plate (P) which is a lever whereby the rear OEM trigger is actuated by forward trigger  250  by means of cable linkage  260 . 
     In sequential views  FIGS. 15-17  depict a preferred cocking method: (1) the rifle is gripped at the ends with the grip  220  pointed toward the torso, (2) the rifle is “broken” to initiate the cocking process using the grip as a fulcrum, and (3) in the final stage of cocking, the pivot point between the air cylinder and the barrel is raised with the hands lowered to ease completion of the final cocking stage. The saddle shaped buttstock  290  produces a sure grip that both enables and eases the foregoing cocking process. 
       FIG. 18  shows an embodiment wherein the buttstock is resting atop a shoulder without the need of a shoulder strap. 
       FIG. 19  depicts an embodiment in a compact carry position wherein the safety is engaged. 
       FIG. 20  shows an embodiment in a ready (aiming) position. The shape, size and positioning of the stock shortens the distance between a gun sight or scope, and the shooter&#39;s eyes when sighting. The form also permits one&#39;s arms to be comfortably flexed and closer to one&#39;s trunk in contrast with the extended arm position assumed with conventional stocks. The stock assembly therefore improves body mechanics, reduces fatigue and provides other surprising advantages flowing therefrom. 
       FIG. 21  in one embodiment, depicts a removable/interchangeable grip wherein the dotted lines represent a stub  230  for attaching a desired grip. 
     It should be understood that the stock, buttstock and other elements of the stock assembly can be made of any plastic, metal or composite. Moving back to  FIG. 7 , preferably, grip  220  is between 10 and 20 degrees of vertical. However, grip  220  can extend at any angle or perpendicularly relative to stock  200  and adjacent to slot  210 . It is conceivable that a grip may be switched and secured from a right side to a left side of the stock depending on user preference. 
     Other advantages flowing from the present invention are the mounting of a scope and/or a bipod along the barrel length. The present invention can be used with a picatinney rail. It is conceivable that certain mechanically assisted means be added to forward trigger  250  to reduce the trigger pull force required. For example, a battery operated servo within the grip ( FIG. 22 b   ) can sense and then augment finger pressure by applying additional pulling force to cable  260 . 
     In an implementation of the invention applicable to both break barrel guns and rifles such as the AR15, a trigger guard  306  ( FIG. 22 a   ) is modified with a slot  307  therein forming a channel along which a actuated drawbar  300  travels. The drawbar is linked to a servo  310  that pulls the drawbar at a rate determined by the movement of auxiliary trigger  308  which is coupled to a potentiometer  320 . When the auxiliary trigger or secondary trigger is drawn, the resistance of the potentiometer is varied which determines the rate of travel of the servo  310  which pulls and forces the drawbar against the primary trigger. Tension may be varied for the auxiliary trigger by a spring or other means that will be appreciated by those having skill in the art. It is therefore possible to reduce the trigger pull force considerably; in the case of air rifles, for example, from 5 lbs to 2 lbs or less, and provide greater accuracy resulting from smoother trigger motion. Alternatives to the servo include a small motor and pulley that winds a wire or cable connecting the drawbar. Any type of potentiometer may be employed including linear potentiometers. 
     While the present invention compared to past stock design lightens a rifle, It is conceivable that other improvements to the conventional break barrel configuration will reduce weight even further. Conceivably, the piston which is typically a steel alloy can be replaced with one of carbon fiber or other lightweight composite. One advantage of a lighter weight piston would be less recoil and greater accuracy. The back spring guide can also be substituted with a lighter material such as carbon fiber or aluminum. 
     In view of the many possible embodiments to which the principles of the disclosed invention may be applied, it should be recognized that the illustrated embodiments are only preferred examples of the invention and should not be taken as limiting the scope of the invention. Therefore, this disclosure is intended to cover such alternatives, modifications, and equivalents as may be included in the spirit and scope of the description in view of the appended drawings and claims.