Abstract:
A firearm bullpup conversion system incorporates a uniquely configured buttstock that conforms to the operator&#39;s shoulder or upper arm to reduce the pull length for a given overall stock length. The system also provides for an auxiliary trigger located in front of the action, an integrated cocking and accessory mounting rail, and a trigger safety.

Description:
BACKGROUND AND SUMMARY 
     This invention relates generally to firearms, and more particularly to stock or conversion kits (a.k.a. “bullpup stock kit”, “bullpup stock system”) which convert a traditional firearm into bullpup configurations. 
     Firearm “bullpup” configurations are discussed in some detail in Wikipedia, some portions paraphrased, summarized, and or quoted herein. Traditionally, firearms using detachable magazines are configured so that fee action of the firearm and fee ammunition magazine are located in front of the trigger. Firearms configured so that the action and the magazine are located behind the trigger of fee firearm are generally referred to as “bullpups”. 
     Bullpup configuration permits a shorter overall weapon for a given barrel length. This is due to the positioning of the action closer to the rear end of the buttstock. This maintains the advantages of a longer barrel in muzzle velocity and accuracy, while improving maneuverability and reducing weight. 
     Traditional firearms users may desire to alter the appearance and function of their more traditionally configured firearm into that of a bullpup for various reasons, including but not limited to improve ergonomics, reduce weight, and reduce overall length without compromising ballistic performance. There is a need for a conversion system that minimizes the requisite expertise and mechanical skill. 
     In converting a firearm to bullpup configuration, the action and the mounting position of the ammunition magazine are moved rearward relative to the butt, but the desired position of the trigger relative to the butt stays the same. This requires the bullpup stock kit to include a mechanism that places an auxiliary trigger relatively in front of the action and in operational communication with the firearm&#39;s original trigger (aka the trigger of a barreled action). The foregoing is usually accomplished with a rigid push-rod type linkage mechanism. The trigger pull characteristics of these mechanisms is generally considered inferior to the trigger pull characteristics of the host firearm. The present invention achieves an advantage over existing systems by providing a tension-type trigger linkage mechanism utilizing a cable. 
     One handed operation is desirable. The compact design of the bullpup configuration entices users to attempt one handed operation. However, traditional bullpup designs are problematic in that the pull length is too long for efficient one-handed operation. “Pull length” is generally defined as the distance from the center of the buttstock to the trigger. Thus, it is an object of this invention to reduce the pull length. 
     An advantage of the present invention is achieved by providing a uniquely designed buttstock resulting in a reduced pull length; a forwardly sloping butt design achieves a shorter pull length by allowing the upper portion of the butt to rest on the shoulder or upper arm of the user, thus improving one-handed operation. 
     Due to the rearward placement of the firearm action relative to the butt in a bullpup configured firearm, a mechanism that places an auxiliary cocking handle forward of the action and in operational communication with the firearm&#39;s original cocking handle is a desirable feature. Also, due to the rearward placement of the firearm action relative to the butt in a bullpup configured firearm, the original sights cannot be used. Thus, it is desirable to provide auxiliary sights or an attachment platform for auxiliary sights. 
     Another advantage is achieved by connecting the auxiliary sights and/or the attachment platform for the auxiliary sights directly to the firearm receiver, because doing so provides a more stable and therefore accurate arrangement. 
     Yet another advantage is achieved by combining the aforementioned auxiliary cocking handle and attachment platform for auxiliary sights into an assembly that is connected directly to the receiver. This arrangement achieves the aforementioned advantages as well as requiring less volume and mass than would be needed for the separate components. 
     In the various embodiments described, the present invention is advantageous in that it requires minimal gunsmithing knowledge or mechanical expertise to install, provides a configuration that conforms to the shoulder or upper arm and places the firearm action close to the body and shortens the pull length, provides an auxiliary trigger forwardly positioned in front of the action and the magazine, provides a an auxiliary cocking handle forwardly positioned in front of the action, and provides a stable mounting platform for auxiliary sights. 
     In one embodiment, a bullpup conversion system comprises, a grip adapted to be gripped by a user in such a way so as to allow the user to engage an auxiliary trigger; a trigger linkage mechanism operatively engaging the auxiliary trigger and a first trigger of a barreled action, wherein the linkage mechanism includes a cable; the grip and auxiliary trigger being located in front of the barreled action; a trigger safety for restraining the auxiliary trigger in a non-firing position; a butt having a rearwardly oriented surface adapted to conform to the upper surface of the operator&#39;s shoulder-upper arm region; a sight and/or scope accessory mounting rail; a cocking handle linkage mechanism having an auxiliary cocking handle for operatively engaging a first cocking handle; wherein the sight and/or scope accessory mounting rail and cocking handle linkage mechanism comprise an assembly (aka a combined system); the foregoing enclosed within a two piece chassis system. It is to be understood that the term “chassis”, as used herein, is interchangeable with, and in the nature of, an “enclosure” and thus is not limited in meaning to a frame or subframe. 
     In one embodiment, the present invention is configured to work with a Ruger 10/22 rifle (“Ruger” and “10/22” are trademarked). Accordingly, those of skill in the art will appreciate that the various components described herein are sized accordingly. In one embodiment, a bullpup conversion system comprises, left and right chassis portions configured to receive the barreled action of a rifle (e.g. Ruger 10/22 rifle). 
     In one embodiment, the rear portion of the chassis comprises a butt with a concave contoured surface that is angled forward from top to bottom. This configuration allows the rear end of the stock to rest on the upper surface of the operator&#39;s shoulder or arm and also reduces the pull length, over traditional butt designs for a given overall stock length. A rail is secured to the top of the receiver using a connector plate that is secured to the factory installed scope mount holes. The rail provides a mechanism that connects auxiliary cocking levers on either side of the rail to the cocking handle on the barreled action. By operating either auxiliary cocking handle, the cocking handle on the barreled action may be operated. 
     It is to be understood that the term “action” as used herein throughout includes the bolt, receiver and trigger mechanism of the firearm. The firearm used in some embodiments is a Ruger 10/22 rifle, commonly referred to as a 10/22. The 10/22 is typically chambered to fire .22 Long Rifle caliber ammunition. 
     As described herein, the present invention is directed towards a firearm stock kit that may be used to convert a traditionally configured firearm into bullpup configuration. The stock incorporates a uniquely configured buttstock that conforms to the operator&#39;s shoulder or upper arm and reduces the pull length for a given overall stock length. The firearm stock kit also provides for an auxiliary trigger, an integrated cocking and accessory mounting rail, and a trigger safety. Those of skill in the art will appreciate other objects and advantages in addition to those described herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       It is to be expressly understood that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention. 
         FIG. 1  is a side perspective view of the right side of a 10/22 rifle&#39;s barreled action equipped with a bullpup stock kit in accordance with the present invention. 
         FIG. 2  is a side perspective view of the left side of the bullpup-configured firearm shown in  FIG. 1 . 
         FIG. 3  is an exploded view showing the internal arrangement of the bullpup-configured firearm shown in  FIGS. 1 and 2 . 
         FIG. 4  is a side perspective view of the right side of the bullpup stock kit trigger linkage mechanism and safety. 
         FIG. 5  is a side perspective view of the right side of the bullpup stock kit cocking/accessory rail mechanism. 
         FIG. 6  is a side cutaway view of the right side of the bullpup stock kit cocking/accessory rail mechanism. 
     
    
    
     REFERENCE NUMERALS IN DRAWINGS 
     The table below lists the reference numerals employed in the figures, and identifies the element designated by each numeral.
       1  Bullpup configured rifle     2  Bullpup Stock Kit     3  Barreled action     4  Left Stock Body portion     5  Right Stock Body portion     6  cocking/accessory rail     7  auxiliary trigger     8  auxiliary trigger safety     9  trigger linkage mechanism     10  Shell Casing Deflector     11  Barrel Shroud     12  Barrel Shroud—Left half     13  Barrel Shroud—Right half     14  chassis     15  Action     16  Barrel     17  10/22 trigger     18  Trigger Housing     19  Internal rib in chassis     20  Sling attachment point     21  Sling attachment point—left portion     22  Sling attachment point—right portion     23  Shark fin buttstock     24  chassis screw     25  accessory threaded insert     26  butt     27  10/22 rear sight channel     28  10/22 rear sight     29  trigger support plate     30  trigger pivot pin     31  linkage cable     32  trigger cable hole     33  cable set screw     34  cable block     35  trigger slide bar     36  slide bar cable screw     37  mounting screw     38  slide bar retaining plate     39  trigger actuating pin     40  trigger spring     41  trigger spring screw     42  cable tensioner     43  cable tension pin     44  tension spring     45  tension spring screw     46  trigger block     47  safety pivot screw     48  safety detent pin     49  detent spring     50  support plate mounting screws     51  rail body     52  cocking bar     53  cocking handle     54  cocking handle screw     55  cocking handle screw insert     56  cocking spur     57  cocking spur screws     58  cocking bar spring     59  cocking bar spring screw     60  10/22 receiver     61  key plate     62  accessory rail     63  key plate opening     64  10/22 cocking handle     65  shell deflector screws     66  cable tensioner frame     67  butt upper portion     68  butt middle portion     69  butt lower portion   

     DETAILED DESCRIPTION 
     Turning now to the drawings in which like reference characters indicate corresponding elements throughout the several views, as used herein, the word “front” or “forward” corresponds to where the muzzle end of the barrel is located (i.e., to the right as shown in  FIGS. 1, and 3 through 6 , and to the left in  FIG. 2 ); “rear” or “rearward” or “back” corresponds to the direction opposite where the muzzle end of the barrel is located (i.e., to the left as shown in  FIGS. 1, and 3 through 6 , and to the right in  FIG. 2 ). 
     As shown in  FIGS. 1-3 , the present invention is directed to a bullpup stock kit, designated by reference numeral  2 , for use with the barreled action  3  of a rifle. The combination of the barreled action  3  and the bullpup stock kit  2  is referred to as the bullpup configured firearm, or simply bullpup, and is designated by reference number  1 . 
     Best shown in the exploded view of  FIG. 3 , the bullpup stock kit  20  comprises a left stock body portion  4 , a right stock body portion  5  (aka left and right chassis portions), a cocking/accessory rail  6 , auxiliary trigger  7 , auxiliary trigger safety  8 , a trigger linkage mechanism  9 , a shell casing deflector  10 , and a barrel shroud  11  that comprises a left shroud portion  12  and a right shroud portion  13 . The combination of the left stock body portion  4  and the right stock body portion  5  are collectively referred to herein as the chassis  14 . Also shown in  FIG. 3  is a detailed view of a Ruger 10/22 barreled action  3 . The barreled action  3  is comprised of an action  15  (receiver and bolt) and a barrel  16 . The action  15  also has a trigger  17 , and a trigger housing  18 . 
       FIGS. 1 through 3  show detailed illustrations of the chassis  14 . In the preferred form, the chassis  14  is injection molded from a stiff, resilient polymer, though the particular material is not essential to the present invention. The chassis  14  includes internal ribs  19  that provided structural support for the outside surface of the chassis  14  and also support the barreled action  3 , the trigger linkage mechanism  9 , and the cocking/accessory rail  6 . The chassis  14  has sling attachment points  20 . In the preferred embodiment, the sling attachment points are machined from 6061 T6 aluminum and are of the quick-disconnect socket type. The sling attachment points  20  consist of a left portion  21  and a right portion  22  that are molded into the left stock body portion  4  and the right stock body portion  5 , respectively. The left portion  21  and the right portion  22  of the sling attachment points  20  are connected in the middle by means of a screw (not shown) and thus help secure the left stock body portion  4  and the right stock body portion  5  together. The left stock body portion  4  and the right stock body portion  5  are further secured together by means of chassis screws  24  and threaded inserts (not shown). In the preferred form, the chassis also includes threaded inserts  25  for the attachment of accessory rails. 
       FIGS. 1 through 3  show detailed illustrations of the chassis&#39;  14  butt area  26 . The surface of the butt  23  has a ribbed texture which prevents the bullpup  1  from slipping off of the operator&#39;s shoulder or upper arm during firing. The butt  26  is configured so that it is angled forward from top to bottom. This arrangement has two advantages over traditionally configured butts. The first advantage is to allow the butt  26  of the bullpup  1  to rest on top of the user&#39;s shoulder or upper arm to facilitate one-handed operation of the bullpup  1 . The second advantage is to reduce the distance from the center of the butt  26  to the auxiliary trigger  7 , commonly referred to as the length of pull (or pull length), for a given overall chassis length. This allows the center of mass of the bullpup  1  to be held closer to the user&#39;s body when it is shouldered. 
       FIGS. 1 through 3  also show the 10/22 rear sight channel  28  in the chassis  14 . The 10/22 rear sight channel  28  allows the factory rear sight  29  to remain in place on the barrel  16  when the barreled action  3  is installed in the chassis  14 . Those of skill in the art will appreciate that such channel is sized commensurate with a given sight (e.g. 10/22). 
       FIGS. 1 through 3  show detailed illustrations of the shell deflector  10  and the barrel shroud  11 . The shell deflector  10  is secured to the chassis  14  with screws and inserts  65 . The rearward end of the barrel shroud  11  is sandwiched between the left stock body portion  4  and the right stock body portion  5  during assembly of the bullpup configured firearm  1 . In the preferred form, the shell deflector  10  and barrel shroud  11  are injection molded from a stiff, resilient polymer, though the particular material is not essential to the present invention. 
       FIG. 4  shows details of the trigger linkage mechanism  9 . The trigger linkage mechanism  9  is comprised of the following assembly: the auxiliary trigger  7  is attached to the support plate  29  by means of a pivot pin  30 ; a linkage cable  31  is attached to the top of the auxiliary trigger  7  through a hole  32  and secured with a set screw  33 ; the linkage cable extends to the rear of the support plate  29 , passes around the cable block  34 , and is secured to the end of the trigger slide bar  35  by means of a screw  36 ; the cable block  34  is secured to the support plate with mounting screws  37 ; the trigger slide bar is supported on either side by retaining plates  38  secured to the support plate with mounting screws  37 ; and, the trigger actuating pin  39  is located at the forward end of the trigger slide bar  35  in close proximity to the surface of the trigger  17 . The auxiliary trigger  7  and trigger slide bar  35  are retained in a forward position by means of a trigger spring  40  that is connected between the trigger actuating pin  39  and the support plate  29  by means of a screw  41 . A cable tensioner  42  comprises a frame  66  machined into the front side of the cable block  34  that houses a cable tension pin  43  which encircles the linkage cable  31  at one end and is connected to the tension spring  44  at the other. The tension spring  44  is in turn connected to the frame  66  with the tension spring screw  45 . The trigger linkage mechanism  9  also includes auxiliary trigger safety  8  that prevents rearward movement of the auxiliary trigger  7  by means of the trigger block  46  that protrudes from the top surface of the auxiliary trigger safety  8 . The safety is mounted to the chassis  14  by means of the safety pivot screw  47 . The auxiliary trigger safety  8  is retained in either the “on” or “off” position by means of a pin  48  and a spring  49  that are mounted in the chassis below the auxiliary trigger safety  8 . The trigger linkage mechanism  29  is secured to the left stock body portion  4  using the support plate mounting screws  50 . 
     Operation of the trigger linkage mechanism  9  is as follows: rearward pressure on the auxiliary trigger  7  places tension on the linkage cable  31 ; the linkage cable  31  pulls the trigger slide bar  36  rearward; the trigger actuating pin  39  contacts and moves trigger  17  rearward which in turn fires the bullpup configured firearm  1 . Rotation of the auxiliary trigger safety  8  in a counterclockwise motion (as viewed from the top) moves the trigger block  46  into position and prevents rearward movement of the auxiliary trigger  7 . 
     In the preferred form, the auxiliary trigger  7 , auxiliary trigger safety  8 , support plate  29 , cable tension pin  43 , and slide bar retaining plates  38  are machined from 6061 T6 aluminum, the cable block  34  and trigger slide bar  35  are machined from Delrin, and the linkage cable  31  is Kevlar or stainless steel, though the particular materials are not essential to the present invention. 
       FIGS. 5 and 6  show details of the cocking/accessory rail  6 . The cocking/accessory rail  6  is comprised of the following assembly: the rail body  51  houses the cocking bar  52 ; the cocking handles  53  are secured to the cocking bar with the cocking handle screws  54  that are connected at the center of the cocking bar by the cocking handle screw insert  55 ; the cocking spur  56  is connected the rearward end of the cocking bar  52  with screws  57 . The cocking bar  52  is retained in a forward position by the cocking bar spring  58 . The rearward end of the cocking bar spring  58  is connected to the forward end of the cocking bar  52  by a screw  59 . The forward end of the cocking bar spring  58  is connected to the forward end of the rail body  51  by a nut and bolt  60 . The rail body  51  is connected to the 10/22 receiver  60  using: the factory installed scope mounting holes (not shown); a key plate  61 ; and mounting screws  62 . The rail body  51  has an accessory rail  62  along the top surface that facilitates the attachment of sights, scopes, lasers, flashlights, or other items ancillary to operation of the bullpup firearm  1 . In the illustrated embodiment the accessory rail is of the type generally referred to as a “Picatinny rail” and manufactured in accordance with the specifications in MIL-STD-1913. Other attachment surfaces which facilitate the attachment of optics and iron sights could be used in place of the accessory rail shown and described herein. 
     In the preferred embodiment, the rail body  51  is machined from extruded 6061 T6 aluminum stock, the cocking bar  52  is machined from Delrin, and the cocking spur  56  is machined from 6061 T6 aluminum, though the particular materials are not essential to the present invention. 
     The cocking/accessory rail  6  is attached to the 10/22 receiver  60  as follows: the key plate  61  is attached to the forward most two factory installed mounting holes on the 10/22 receiver  60  using screws  62 ; the cocking/accessory rail  6  is positioned on top of the 10/22 receiver  60  such that the key plate extends through the wide part of the key plate opening  63  in the rail body  51 ; the cocking accessory rail is slid toward the rear until the key plate  61  is fully engaged in the narrow part of the key plate opening  63 ; and, the cocking/accessory rail  6  is secured in position on the 10/22 receiver  60  using the rearward most two factory installed mounting holes (not shown) and screws  62 . 
     Operation of the cocking/accessory rail is as follows: The cocking handle  54  is pulled to the rear which in turn pulls the cocking bar  52  to the rear; the cocking spur  56  that is connected to the rear end of the cocking bar  52  engages and moves the 10/22 cocking handle  64  rearward which in turn operates the 10/22 action  15 . 
     Assembly of the complete Bullpup configured firearm  1  comprises the following steps: The trigger linkage mechanism  9  is secured into the left stock body portion  4 ; the cocking/accessory rail  6  is attached to the top of the barreled action  3  as described above; the barreled action  3  and cocking accessory rail  6  combination is positioned into the left stock body portion  4 ; the right stock body portion  5  is placed over the left stock body portion  4  and secured with the chassis screws  24 . 
     The exact shape of the chassis  14  exterior surfaces may be varied without departing from the scope of the invention disclosed herein. 
     In an alternate embodiment, the barrel shroud  11  could be omitted entirely without departing from the spirit of the present invention. In lieu of the barrel shroud  11 , a flush bushing (not shown) located at the barrel opening in the chassis  14  could replace it. 
     In still another alternate embodiment, iron sights could be provided as part of the cocking/accessory rail  6  without departing from the scope of the present invention. 
     In yet another alternate embodiment, the shell casing deflector  10  could be omitted from the bullpup configured firearm  1  without departing from the scope of the present invention. 
     The foregoing descriptions and drawings should be considered as illustrative only of the general principles of the invention. This invention is not limited for use with the barreled actions of Ruger 10/22 rifles; rather it may be used with any firearm&#39;s barreled action which has similar operating features and dimensions. Numerous applications of the present invention will readily occur to those skilled in the art. Therefore, it is not desired to limit the invention to the specific examples disclosed or the exact construction and operation shown and described. Rather, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention. 
     In one embodiment, left and right stock body portions  4 ,  5  are fitted together so as to form a case having butt portion  26 . Butt portion  26  has rearwardly oriented surface (middle portion  68 , upper portion  67 , and lower portion  69 ) adapted to conform to and engage the user&#39;s shoulder-upper arm region. 
     In one embodiment (e.g.  FIGS. 1-3 ), lower portion  69  is relatively forward of upper portion  67 , and middle portion  68  is concave—relative to the user&#39;s shoulder.