Abstract:
The bolt hold-open system is a firearm bolt locking or holding mechanism for an AK-47 or similar firearm capable of automatically keeping the bolt of the firearm in an open position when the firearm magazine is empty. The bolt hold-open system includes a locking assembly and a modified magazine. The bolt hold-open system also provides a manual control for keeping the bolt in an open position and for releasing the bolt. The system prevents the bolt carrier from closing while there is an empty magazine in the gun, but can be easily activated to release the bolt when the magazine is removed or a non-empty magazine is in the magazine receiver. The system requires minimal modifications to the firearm and magazine and is easily adaptable to firearms similar to the AK-47 that fire ammunition in a wide range of calibers and configurations.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This nonprovisional application claims the benefit of co-pending U.S. Provisional Patent Application Ser. No. 61/835,633, filed on Jun. 16, 2013, which is incorporated herein in its entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention relates to the general technical field of firearms, and particularly to a system for locking the bolt of the firearm in an open position, and specifically to an economical and easily installed bolt hold-open system including a modified magazine for AK-47 firearms and firearms that are variants of the AK-47. 
       BACKGROUND OF THE INVENTION 
       [0003]    The AK-47, or Kalashnikov rifle, is one of the most common firearms globally. Its simple and reliable design makes it economical to manufacture and easy to maintain in the field. While the AK-47 is a versatile weapon, it does lack some features that would improve its usefulness in combat. 
         [0004]    One of the most problematic gaps in the AK-47&#39;s design is the lack of an automatic bolt hold-open. When the last cartridge in the firearm&#39;s magazine is spent, the bolt returns to the closed position without picking up a cartridge. After replacing the empty magazine with a full magazine, it is necessary to manually pull back the bolt to chamber the first cartridge of the new magazine. Although this action only requires a few seconds, it is distracting and annoying, or worse in the case where every second counts. Additionally, when at a shooting range, range officers may at times require the bolt to be held in the open position for safety so a bolt hold-open would be beneficial. 
         [0005]    A mechanism that would automatically hold the bolt open when the last round was ejected from the magazine, while allowing the bolt to be easily released when a new magazine is in place, would remove the necessity of manually chambering the new round, would satisfy shooting range regulations, and would provide a significant advantage in speed and convenience of changing magazines. Such a device would also minimize mental distraction, allowing the firearm user to direct more of his or her attention to the surroundings. 
         [0006]    U.S. Pat. No. 7,261,029 issued to Davis provides a bolt hold-open for an AK-47, but the system disclosed by Davis requires the modification of the bolt carrier, the receiver carrier, and the magazine. A system that limits modifications to the gun is preferable, since it allows the use of a wider variety of replacement parts. Furthermore, the bolt hold-open release mechanism of the system provided in Davis cannot be activated by the trigger hand since the mechanism is high on the gun, and the Davis bolt hold-open can only be released on one side of the gun. A system which allowed the locking mechanism to be released by the trigger hand would be preferable, as would a system that could be easily operated either left- or right-handed. 
         [0007]    Other available retrofit bolt hold-open devices do not hold the bolt fully open. 
         [0008]    Accordingly, there is a need for a bold hold-open system that holds the bolt within the bolt carrier fully open, can be operated with either hand, can be accessed with the trigger hand, and requires no more than minimal modification to the gun. 
       SUMMARY OF THE INVENTION 
       [0009]    The bolt hold-open system of the present invention provides the ability to add a full bolt hold-open to an AK-47, AD-47 variants, and similar guns. The bolt hold-open system includes a locking assembly and a modified magazine. The locking assembly provides a magazine lever that is raised when a modified magazine with a magazine tab is emptied. The magazine lever causes a bolt catch lever to rise into the path of the rifle bolt carrier, preventing it from returning to the closed position. An activator lever disposed on the exterior of the firearm is connected by a connector lever to the bolt catch lever and can be activated manually to release the bolt hold-open locking mechanism or to engage it manually. 
         [0010]    Variations are presented in both the modified magazine and in the locking assembly. These allow the bolt hold-open system to be readily used with the several variants of AK-47 guns, including guns particularly configured to meet specific state laws. 
         [0011]    The bolt hold-open system of the present invention is easily adaptable to guns with a wide variety of calibers and requires minimal or no modifications to the gun itself. Furthermore, existing magazines can be easily adapted to work with this bolt hold-open locking mechanism with minimal changes, and the locking assembly does not interfere with the operation of the gun when unmodified magazines are used. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The preferred embodiments of the invention will hereinafter be described in conjunction with the appended drawings, provided to illustrate and not to limit the invention, where like designations denote like elements. 
           [0013]      FIG. 1  is a right side cut view showing a first embodiment of the present invention mounted in a firearm from the right side of the firearm. 
           [0014]      FIG. 2  is an exterior right side view showing a first aspect of the first embodiment of the present invention from the right side of the firearm. 
           [0015]      FIG. 3  is an exterior left side view showing a second aspect of the first embodiment of the present invention from the left side of the firearm. 
           [0016]      FIG. 4  is a left side cut view showing the first embodiment of the present invention mounted in a firearm from the left side of the firearm. 
           [0017]      FIG. 5  is a perspective view of a first variation of a firearm magazine modified to be compatible with the first or third embodiment of the present invention. 
           [0018]      FIG. 6  is a left side cut view of a firearm showing a second embodiment of the locking mechanism (locking assembly) and a second variation of a firearm magazine modified to be compatible with firearms that do not afford the addition of a rear tab on the magazine. 
           [0019]      FIG. 7  is a perspective view of the second variation of the firearm magazine modified to be compatible with a second embodiment of the present invention. 
           [0020]      FIG. 8  is a left side view of the locking mechanism of the first embodiment of the present invention from the left side of the firearm. 
           [0021]      FIG. 9  is a right side view of the locking mechanism of the first embodiment of the present invention from the right side of the firearm. 
           [0022]      FIG. 10  is a left side view of the locking mechanism of a third embodiment of the present invention from the left side of the firearm. 
           [0023]      FIG. 11  is a right side view of the locking mechanism of the third embodiment of the present invention from the right side of the firearm. 
           [0024]      FIG. 12  is a right perspective view of the locking mechanism of the third embodiment of the present invention. 
           [0025]      FIG. 13  is a partial perspective view of one end of the locking mechanism of the third embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0026]    In an unmodified firearm, the action of pulling the trigger will release a spring-loaded hammer, which will rise up and strike a firing pin. If a cartridge is in the chamber of the gun, the firing pin will strike the cartridge primer, igniting the powder charge in the cartridge. The force generated by the explosion of the powder charge will send the bullet forward out the barrel of the gun and will at the same time push the bolt backward far enough to eject the spent cartridge. The bolt is then pushed forward again by the action of the return spring, and as the bolt returns to the starting position it picks up and chambers the next cartridge from the magazine. If there are no additional cartridges in the magazine, the bolt returns to the starting position without loading a cartridge into the chamber, and upon replacement of the magazine the bolt must be manually operated to load the first cartridge into the chamber. 
         [0027]    The bolt hold-open system of the present invention, shown generally as reference number  100  ( FIG. 1 ), prevents the bolt from returning to the starting position when the last cartridge is fired from a modified magazine. The bolt hold-open system includes both a locking assembly  105  ( FIGS. 8-9 ) and a modified magazine  260  ( FIG. 5 ),  270  ( FIG. 7 ). The locking assembly  105  provides a magazine lever  140  that is raised when the modified magazine  260 ,  270  with a magazine tab  165  ( FIG. 5 ),  167  ( FIG. 7 ) is emptied. The magazine lever  140  causes an upper carrier-interacting portion  112  ( FIGS. 8-9 ),  119  ( FIGS. 10-11 ) of a bolt catch lever no to rise into the path of the rifle bolt carrier  230  ( FIGS. 1 ,  4 ,  6 ), preventing it from returning to the closed position. In the first embodiment, the upper carrier-interacting portion  112  of bolt catch lever no rises to interact with the knob on the back of the carrier  230 , while in the third embodiment, the upper carrier-interacting portion  119  of bolt catch lever no is designed to catch on the front of the carrier  230 . A manual activator lever  130  disposed on the exterior of the firearm is connected by a manual connector lever  120  to the bolt catch lever no and can be activated manually to release the locking assembly  105  or to engage it manually. 
         [0028]    Now in detail, referring to cut view  FIG. 1 , the bolt hold-open system  100  is depicted installed in a gun. The bolt hold-open system  100  of the current invention is shown mounted as a modification to a standard AK-47, but can be used as a modification to a wide variety of different AK-47 variants and can be used alongside many common AK-47 modifications. 
         [0029]    As seen in  FIG. 1  and the detail views of  FIGS. 8-9 , the piece of the locking assembly that engages the rifle bolt carrier  230  is the upper carrier-interacting portion  112  of the bolt catch lever no. The bolt catch lever no is a relatively thin metal sheet, particularly shaped with apertures, cut-outs and pivot points. The bolt catch lever no is shaped with an aperture  221  around hammer pivot pin  220  toward the front configured to allow the bolt catch lever no to rotate around the hammer pivot pin  220  ( FIG. 1 ). The hammer pin aperture, defined by generally circular edge  221  ( FIG. 8 ), is sized and shaped to accommodate the hammer pivot pin  220 . The rear end of the bolt catch lever no of the first embodiment is shaped into two rearwardly projecting portions or projections, the upper carrier-interacting portion  112  and a lower prong  113  ( FIGS. 4 ,  8 ,  9 ). The prongs form the upper and lower rearward end of the bolt catch lever  100  disposed rearward of magazine lever pivot  115  and rearward of edge  222 . The bolt catch lever no is split into two prongs to avoid interfering with the operation of the safety tab of the gun. In order to install the locking assembly  105  it may be necessary to trim off a small amount of metal from the top right of the safety device. 
         [0030]    The bolt catch lever no has a trigger pin cut-out defined by trigger pin cut-out edge  222  on the lower side spaced as necessary for gun model variations to allow the bolt catch lever no to rotate freely without engaging with the trigger pivot pin  210 . The bolt catch lever no also has a magazine lever pivot  115  mounted forward of the trigger pivot pin  210 . The bolt catch lever lower prong  113  ( FIG. 4 ) is attached to the front end of a connector lever  120  ( FIG. 1 ) at a connector lever pivot  125 . The connector lever  120  is non-rotatably connected at the rear end to an activator lever  130  ( FIG. 2 ) at an activator lever connector  135 . The activator lever connector  135  passes through a hole in the gun casing  250  ( FIG. 2 ) and thus the activator lever  130  ( FIG. 2 ) is disposed on the exterior of the gun  200 . Many firearm variants provide an unused hole in this position, and the connector lever  120  can be sized appropriately for the firearm to use a preexisting hole, however, if a hole is not provided it is necessary to drill the hole in the gun casing  250  ( FIG. 2 ) for the activator lever connector  135  to pass through. 
         [0031]    A magazine lever  140  is rotatably connected to bolt catch lever no at the magazine lever pivot  115 . The magazine lever  140  extends rearward from the magazine lever pivot  115  so that the rear tab  143  ( FIG. 8 ) of the magazine lever  140  rests on the trigger pivot pin  210  ( FIG. 1 ). The magazine lever  140  also extends forward in somewhat of an arc  146  from the magazine lever pivot  115 , over the hammer pivot pin  220 , then down to distal end  144  to lie substantially along the bottom casing of the gun  200 . Surface  149  is adjacent to the bolt catch lever no, as shown in  FIG. 8 . 
         [0032]    A magazine catch  145  extends upward then forward in a roughly “L”-shaped form from the distal end  144  of bolt catch lever no. The magazine catch  145  is configured so that the magazine tab  165  ( FIG. 5 ) mounted on the magazine follower  263  ( FIG. 5 ) will raise the magazine catch  165  when the magazine  260  ( FIG. 5 ) is emptied. When the magazine catch  145  is raised by the magazine tab  165  the magazine lever  140  will act as a second class lever with the magazine lever rear tab  143  resting on the trigger pivot pin  210  serving as a fulcrum, causing the magazine lever pivot  115  to rise. Since the magazine lever pivot  115  connects to the bolt catch lever no, the bolt catch lever will be rotated upward with the hammer pivot pin  220  serving as a fulcrum. This will cause the bolt catch lever upper carrier-interacting portion  112  to move upward into the path of the bolt carrier  230  carrying the bolt, preventing it from returning to the starting position. After the magazine  240  ( FIG. 5 ) is ejected, the magazine tab  165  ( FIG. 5 ) will no longer be holding the bolt catch lever no in place, but the tension of the bolt carrier  230  pressing on the bolt catch lever upper carrier-interacting portion  112  will keep the bolt catch lever no in place until the activator lever  130  ( FIG. 2 ) is pressed down. When the activator lever  130  ( FIG. 2 ) is pressed down, it will rotate causing the connector lever  120  ( FIG. 1 ) to rotate as well. The connector lever  120  is connected at the forward end to the bolt catch lever lower prong  113  ( FIG. 4 ), so the rotation of the connector lever  120  will cause the bolt catch lever no to rotate downward around the hammer pivot pin  220 . This downward rotation will cause the bolt catch lever upper carrier-interacting portion  112  to lower out of the path of the bolt carrier  230 , allowing the bolt carried by bolt carrier  230  to return to its starting position. If a new magazine  240  ( FIG. 5 ) is inserted before activating the activator lever  130 , the bolt will load the first cartridge from the new magazine into the chamber while returning to a closed position, in accordance with its typical functionality. 
         [0033]      FIG. 2  illustrates the exterior of a gun fitted with the bolt hold-open of the current invention. An activator lever  130  is attached to the activator lever connector  135  which extends through the gun housing  250 . The activator lever  130  is elongated and extends toward the front of the gun. The forward end of the activator lever  130  is molded into a finger grip  137  that extends away from the gun body to allow the activator lever  130  to be easily activated by a shooter&#39;s finger. 
         [0034]      FIG. 3  depicts an exterior view of a second aspect of the first embodiment of the bold hold-open of the current invention. In this aspect of the invention, the activator lever connector  135  is configured to extend across the body of the gun and through an aperture in the left side of the gun housing  250  to form a left-side activator lever connector  155 . The left-side activator lever connector  155  is non-rotatably connected to the left-side activator  150 . The left-side activator lever  150  can be configured to extend forward or rearward from the left-side activator lever connector  155 , but is shown in this embodiment extending rearward from the left-side activator lever connector  155 . The end of the left-side activator lever  150  opposite the left-side activator lever connector  155  is molded into a left-side finger grip  157  that extends away from the gun body to allow the left-side activator lever  150  to be easily activated by a right-handed shooter&#39;s thumb or a left-handed shooter&#39;s finger. The left-side activator lever  150  ( FIG. 3 ) can be used in addition to or in replacement of the activator lever  130  ( FIG. 2 ) on the right side of a gun. In the case where it is used in addition to the activator lever  130  ( FIG. 2 ), the holes for the left-side activator lever connector  155  ( FIG. 3 ) and the right-side activator lever connector  135  ( FIG. 2 ) must be aligned so that the left-side activator lever connector  155  ( FIG. 3 ) and the right-side activator lever connector  135  ( FIG. 2 ) are co-linear and non-rotatably connected. In this case, the left-side activator lever connector  155  ( FIG. 3 ) and the right-side activator lever connector  135  ( FIG. 2 ) may be preferably formed as a single component. 
         [0035]      FIG. 4  provides a cut view from the left side of the gun. The bolt catch lever lower prong  113  is visible in this view, in addition to the components discussed in  FIG. 2 . 
         [0036]      FIG. 5  illustrates a first modified magazine  260  modified to work with the bolt hold-open of the current invention. The modified magazine  260  is a standard magazine (compatible with the modified firearm) having a body  265  with the addition of a magazine tab  165  attached to the rear of the magazine follower  263 . The magazine tab  165  is configured to extend in an arc upward and back at an angle to engage with the magazine catch  145  ( FIGS. 1 ,  4 ,  8 ,  9 ) when an empty magazine  260  is inserted into the firearm  200 . When the magazine  260  is loaded with cartridges, the magazine follower  263  is depressed and the magazine tab  165  does not extend upward sufficiently to activate the magazine catch  145  when inserted into the firearm  200 . As cartridges are removed from the magazine  260  through firing the gun or manually activating the chamber, the magazine follower  263  rises until the magazine tab  165  extends out from the magazine housing  265 . The magazine tab  165  is sized so that when the magazine  260  is empty the magazine tab  165  will engage with the magazine catch  145  ( FIG. 1 ), activating the bolt hold-open device. 
         [0037]    The bolt hold-open system  100  requires the use of a modified magazine in order to provide the improved functionality of automatically holding the bolt open when the magazine is empty. However, a firearm modified with the locking assembly  105  of the bolt hold-open system too of the present invention can nevertheless be used with unmodified magazines. If an unmodified magazine is used in a firearm modified with the locking assembly  105  must be manually activated by raising the activator lever  130  ( FIG. 2 ). 
         [0038]    Some firearms that are fundamentally compatible with the locking assembly  105  of the current invention nevertheless have a cartridge chambering mechanism that does not allow for the addition of a rear tab to the magazine.  FIG. 6  illustrates a second embodiment of the locking assembly  105  and a second alternative variation of the modified magazine of the bolt hold-open system too for use in such firearms. In this aspect an alternative magazine  270  is used with a magazine side tab  167  mounted to the front right side of the alternative magazine follower  273 . The magazine side tab  167  extends in an arc upward and to the right to engage with the magazine side catch  147  ( FIG. 6 ). 
         [0039]      FIG. 7  provides a perspective view of a standard alternative magazine  270  modified for use in the second alternative embodiment of the locking assembly  105 . Like in the magazine  240  ( FIG. 5 ) that is compatible with a rear magazine tab  165  ( FIG. 5 ), when the alternative magazine  270  has cartridges in it, the magazine side tab  167  does not extend upward sufficiently to engage the magazine side catch  147 . As the magazine  270  is emptied, the alternative magazine follower  173  rises, causing the magazine side tab  167  to rise as well. The magazine side tab  167  is sized so that when the alternative magazine  270  is empty of cartridges the magazine side tab  167  will extend sufficiently out of the body  265  of alternative magazine  270  to push up the magazine side tab  167  to engage with the magazine side catch  147 , thus activating the locking assembly  105 . 
         [0040]    A third embodiment of the locking assembly  105  is seen in  FIGS. 10-13 . The locking assembly  105  of this third embodiment is similar to the locking assembly  105  of the first embodiment of  FIGS. 1-4 ,  8 - 9  with a variation in the piece of the bolt hold-open that engages the rifle bolt carrier  230 , which in this embodiment is the upper carrier-interacting portion  119  of the bolt catch lever no. 
         [0041]    The rear end of the bolt catch lever no of the third embodiment is shaped into one rearwardly projecting portion lower prong  113  and an upper carrier-interacting portion  119 . The upper carrier-interacting portion  119  is an upwardly extending portion at the rear of lever no. The upper carrier-interacting portion  119  has a step- or hook-shaped upper engagement section, best seen in  FIG. 13 . For use with most AK-47 variants, the upper carrier-interacting portion  119  will extend slightly higher than the upper carrier-interacting portion  112  of the first embodiment. The top front edge of the hook-shaped upper engagement section is positioned above the cut-out defined by edge  222  on the lower side of bolt catch lever no and, in one aspect, may be generally centered over the cut-out. The hook-shaped upper engagement section extends generally horizontally from the top front edge to the top back edge. The top back edge of upper carrier-interacting portion  119  is positioned above the forward portion of bolt catch lever lower prong  113 . The upper carrier-interacting portion  119  of the third embodiment does not extend as far rearward as the upper carrier-interacting portion  112  of the first embodiment. 
         [0042]    The bolt catch lever no of the third embodiment functions as described above in the first embodiment, with the change that the hook-shaped upper engagement section of the upper carrier-interacting portion  119  rises into the path of the rifle bolt carrier  230  and engages the front of the rifle bolt carrier  230  instead of the rear as in the first embodiment. The hook or step shape may be slightly wider or taller, as needed to allow the hooked-shaped upper engagement section of the upper carrier-interacting portion  119  to go around or avoid the edge of the rail of the gun interior. 
         [0043]    The magazine lever  140  (rotatably connected to bolt catch lever no at the magazine lever pivot  115 ) of the third embodiment has a half-arch shaped rear tab  143  that ends in a generally horizontal edge  151 , in contrast to the straight tab  143  of the first embodiment. 
         [0044]    Though not depicted, the locking assembly  105  of the third embodiment may also be used with the alternative magazine follower  173  and the alternative magazine side tab  167  of the second embodiment of the locking assembly  105 . The locking assembly  105  of the third embodiment may also be used with either the left-side activator lever connector  155  ( FIG. 3 ), the right-side activator lever connector  135  ( FIG. 2 ), or the combined left-side activator lever connector  155  and the right-side activator lever connector  135 . 
         [0045]    The locking assembly  105  of the third embodiment provides all of the functionality of the locking assembly  105  of the first embodiment. The third embodiment of the locking assembly  105  is useful in AK-47 variants that have been conformed to fall within the requirements of the laws of multiple states of the United States. These laws require the removal of the knob on the back of rifle bolt carrier  230  that is engaged in the first embodiment. 
         [0046]    To use the bolt hold-open system  100 , if a gun has been fired and there are no additional cartridges in the magazine, the magazine tab  165  ( FIG. 5 ) will raise the magazine catch  165  causing the magazine lever pivot  115  to rise. That rotates the bolt catch lever upward with the hammer pivot pin  220  serving as a fulcrum. The bolt catch lever upper carrier-interacting portion  112 ,  119  moves upward into the path of the bolt carrier  230 , catching it and preventing it from returning to the starting position. Although after the magazine  240  is ejected the tension of the bolt carrier  230  pressing on the bolt catch lever upper carrier-interacting portion  112 ,  119  will keep the bolt catch lever no in place until the activator lever  130  ( FIG. 2 ) is pressed down. When the activator lever  130  ( FIG. 2 ) is pressed down, it will rotate causing the connector lever  120  ( FIG. 1 ) to rotate as well. The connector lever  120  is connected at the forward end to the bolt catch lever lower prong  113  ( FIG. 4 ), so the rotation of the connector lever  120  will cause the bolt catch lever no to rotate downward around the hammer pivot pin  220 . This downward rotation will cause the bolt catch lever upper carrier-interacting portion  112 ,  119  to lower out of the path of the bolt carrier  230 , allowing the bolt carried by bolt carrier  230  to return to its starting position. If a new magazine  240  ( FIG. 5 ) is inserted before activating the activator lever  130 , the bolt will load the first cartridge from the new magazine into the chamber. 
         [0047]    From the foregoing, it will be apparent that the bolt hold-open system  100  of the current invention provides a system and method of operation that is easily adaptable to a wide variety of guns, requires minimal modifications to the guns, is convenient to use, increases the speed with which a shooter can chamber a new round after emptying a magazine, and which allows the use of unmodified magazines without affecting the normal function of the gun. 
         [0048]    Since many modifications, variations, and changes in detail can be made to the described preferred embodiments of the invention, it is intended that all matters in the foregoing description and shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense. Thus, the scope of the invention should be determined by the appended claims and their legal equivalents.