Abstract:
A firearm-magazine interface for replacing an existing firearm-magazine interface of many existing firearms such as assault rifles, namely AK series (AK74, AK47, etc.) provides a lock that holds open the bolt after a last round is fired from a magazine. The firearm-magazine interface also includes a single-button magazine eject. After firing the last round, a bolt-hold lock is urged upwardly in the path of the returning bolt and catches a face of the bolt, thereby locking the bolt open until the magazine is replaced with a replacement magazine, at which time a bolt-hold release paddle pulls the bolt-hold lock downwardly, releasing the bolt to chamber a first round from the replacement magazine.

Description:
FIELD 
       [0001]    This invention relates to firearms and, more particularly, to an adapter for a particular type of firearm that utilizes a different magazine, enhancing the operation of that particular firearm with a bolt-hold-open feature. 
       BACKGROUND 
       [0002]    As disclosed in U.S. Pat. No. 7,261,029 to Davis, the Kalashnikov assault rifle, for example the AK-47, and its variants comprise one of the largest groups of firearms on earth. It has been estimated that over 90 million of these firearms have been produced in dozens of countries since their introduction in the Soviet Union in 1946. Developed primarily as a military weapon, the AK-47 became famous for its simplicity of operation and reliability in extreme conditions of use. Because of its mild recoil, the AK-47 has the capability of delivering effective fully-automatic fire at a range of 300 meters. U.S. Pat. No. 7,261,029 to Davis is hereby incorporated by reference. 
         [0003]    The AK-74 and variants have issues that make it less than optimal for use as a weapon. These rifles (e.g. the AK-74) lack a means to hold the bolt open after the last round is fired from its magazine. When the last round in a magazine is fired, the shooter does not know that the chamber is empty until the shooter attempts to fire. After the last round in the magazine is fired and ejected, the bolt carrier and bolt loudly slide to breech. Chambering another round requires that a loaded magazine be inserted into the receiver and the bolt carrier be pulled back (cocked). This causes the shooter to lower the rifle from a firing position at the shoulder in order to gain sufficient leverage, making the shooter vulnerable to an aggressor. 
         [0004]    It is known to construct detachable firearm magazines such that they will indicate to the shooter when the last cartridge in the magazine has been discharged. The magazines alert the user to the fact that they are empty but do not prevent the forward movement of the bolt carrier and bolt when the magazine is detached from the rifle. Thus, reloading a rifle outfitted with such magazines still requires that the shooter drop the firearm from a firing position to pull the bolt carrier to chamber the first round. 
         [0005]    What is needed is an apparatus that will interface with commonly available magazines that are designed to interface with a bolt-hold-open mechanism of existing firearms with firearms that are not provided with a bolt-hold-open mechanism, thereby providing a bolt-hold-open feature after the last round from the magazine is fired. 
       SUMMARY 
       [0006]    In general, the disclosed firearm-magazine interface replaces the existing firearm-magazine interface of many existing firearms such as assault rifles, namely AK series (AK74, AK47, etc.). The disclosed firearm-magazine interface accepts AR-15 magazines (magazines made for use with an AR-15 variant of firearm) for use with the AK series of firearms (e.g AK74, AK47, etc.). The firearm-magazine interface also provides a mechanism that holds open the bolt after a last round is fired from a magazine and a single-button magazine eject such that, after firing the last round, one button is pressed to eject the empty magazine, a fresh magazine is locked into place and a second lever/button is pressed to release the bolt and chamber a first round from the fresh magazine without having to re-cock the bolt. 
         [0007]    In one embodiment, a firearm-magazine interface is disclosed. The firearm has a spring-loaded bolt and a receiver cross-member pin that is located in the vicinity of a magazine opening. The firearm-magazine interface includes a magazine frame for receiving a magazine, the magazine frame is mounted to the firearm at the magazine opening by, for example, rivets. The magazine contains zero or more rounds of ammunition and the rounds of ammunition are spring-biased toward the firearm when the magazine is installed in the magazine frame. The firearm-magazine interface includes a bolt-hold lock that is slideably interfaced to the magazine frame. A follower contact ledge of the bolt-hold lock interfaces with the magazine follower of the magazine. The magazine follower pushes against the follower contact ledge after the last round has been dispensed from the magazine. The bolt-hold lock has a retracted position whereas the spring-loaded bolt freely passes over the bolt-hold lock and the bolt-hold lock has an extended position, whereas when the magazine is empty, the magazine follower lifts the bold-hold lock to the extended position, thereby a rear side surface (bolt catch edge) of the bold-hold lock engages with the spring-loaded bolt, holding the spring-loaded bolt in an open position after a last round is fired from the magazine. A bolt-hold release lever is moveably interfaced to the magazine frame. Activation of the bolt-hold release lever by a bolt-hold release paddle urges the bolt-hold lock away from the extended position to the retracted position and away from the spring-loaded bolt, thereby releasing the spring-loaded bolt to chamber a round from a new magazine. The bolt-hold lock is braced against the receiver cross-member pin, providing support to counter a force exerted by the returning spring-loaded bolt. 
         [0008]    In another embodiment, a firearm-magazine interface is disclosed. The firearm has a bolt and a receiver cross-member pin that is located in the vicinity of the magazine opening. The firearm-magazine interface includes a magazine frame for receiving a magazine and the magazine frame is mounted to the firearm at the magazine opening by, for example, rivets. The magazine contains zero or more rounds of ammunition and the rounds of ammunition are spring-biased toward the firearm when the magazine is inserted into the magazine frame. The firearm-magazine interface includes a bolt-hold lock slideably interfaced to and held by the magazine frame. The bolt-hold lock is braced against the receiver cross-member pin, providing support to counter a force exerted by the returning spring loaded bolt. A first area of the bolt-hold lock has an angled forward edge that is positioned closest to the chamber of the firearm and a substantially flat bolt-catch edge that is substantially perpendicular to a path of travel of the bolt positioned on a side distal from the chamber. The first area of the bolt-hold lock also has a follower contact ledge. A distal second area of the bolt-hold lock has a bolt-hold lock pin. The follower contact ledge interfaces with the magazine follower and the bolt-hold lock pin interfaces with a bolt release lever that is spring loaded. The spring biases the bolt release lever and, therefore, the bolt-hold lock away from the bolt. A bolt-hold release paddle is moveably interfaced to the magazine frame and interfaced to the bolt release lever such that after a last round of the magazine is chambered, the magazine follower urges the bolt-hold lock into the path of the bolt and after firing of the last round, an angled surface of the bolt momentarily displaces the bolt-hold lock below the path of the bolt. After the bolt passes the bolt-hold lock, the bolt-hold lock returns upward into the path of the returning spring-loaded bolt such that, the bolt is held open by the bolt catch edge. Later, pressing of the bolt-hold release paddle after the bolt is blocked by the bolt catch edge turns the bolt release lever and pulls down on the bolt-hold lock pin, thereby urging the bolt-hold lock away from the bolt, thereby releasing the bolt towards the chamber. 
         [0009]    In another embodiment, a firearm-magazine interface is disclosed. The firearm has a spring-loaded bolt and a receiver cross-member pin that is located in the magazine opening of the firearm. The firearm-magazine interface includes a magazine frame for receiving a magazine. The magazine frame is mounted to the firearm at the magazine opening by, for example, rivets. The magazine contains zero or more rounds of ammunition and the rounds of ammunition are spring-biased by a magazine follower toward the firearm when the magazine is inserted into the magazine frame. The firearm-magazine interface has a bolt-hold lock that is slideably interfaced to and held by the magazine frame. The bolt-hold lock is braced against the receiver cross-member pin, providing support to counter a force exerted by the returning spring-loaded bolt. A first area of the bolt-hold lock has an angled forward edge on a side closest to the chamber of the firearm and a substantially flat bolt-catch edge on a side that is distal from the chamber. The bolt-catch edge is substantially perpendicular to a path of travel of the bolt. The first area of the bolt-hold lock also has a follower contact ledge. The follower contact ledge interfaces with the magazine follower of the magazine. A distal second area of the bolt-hold lock has a bolt-hold lock pin. A bolt release lever is pivotally interfaced to the magazine frame. A first end of the bolt release lever interfaces to the bolt-hold lock pin and a second, distal end of the bolt release lever interfaces to a bolt-hold release paddle. A bolt-hold lock return spring is interfaced between the magazine frame and the bolt release lever, urging the bolt release lever in a direction that biases the bolt-hold lock away from the bolt. A magazine release button is urged outwardly from the magazine frame by a magazine catch spring. The magazine release button is slideably interfaced to a second opposing side of the magazine frame with respect to the bolt-hold release paddle and is mechanically connected to a magazine catch. 
         [0010]    After a last round of the magazine is chambered, the magazine follower urges the bolt-hold lock into the path of the bolt. After firing of the last round, as the bolt returns, an angled surface of the bolt momentarily displaces the bolt-hold lock below the path of travel of the bolt and after the bolt passes the bolt-hold lock, the bolt-hold lock returns upward into the path of travel of the bolt, such that, the returning spring-loaded bolt pushes against the substantially flat bolt-catch edge of the bolt-hold lock, thereby holding the bolt open. Afterwards, pressing the bolt-hold release paddle urges the bolt-hold lock away from the bolt, thereby releasing the bolt towards the chamber. Pressing of the magazine release button moves the magazine catch outwardly away from the magazine, thereby releasing the magazine from the magazine frame. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The invention can be best understood by those having ordinary skill in the art by reference to the following detailed description when considered in conjunction with the accompanying drawings in which: 
           [0012]      FIG. 1  illustrates a partial side plan view of a firearm with an improved firearm-magazine interface. 
           [0013]      FIG. 2  illustrates a partial top plan view of a firearm with the improved firearm-magazine interface. 
           [0014]      FIG. 3A  illustrates a cut-away view of a firearm with the improved firearm-magazine interface along lines  3 - 3  of  FIG. 2  showing a magazine having one remaining round. 
           [0015]      FIG. 3B  illustrates a cut-away view of a firearm with the improved firearm-magazine interface along lines  3 - 3  of  FIG. 2  showing an empty magazine. 
           [0016]      FIG. 4  illustrates an exploded view of the improved firearm-magazine interface. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    Reference will now be made in detail to the presently preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Throughout the following detailed description, the same reference numerals refer to the same elements in all figures. 
         [0018]    Referring now to the  FIG. 1 , a typical firearm  10  with the firearm magazine interface  20  is shown. The firearm is, for example, an AK47 or preferably an AK74, also known as the Kalashnikov assault rifle. Since the firearm  10  is well known to those of ordinary skill in the art, only sufficient detail will be provided for a full understanding of the manner in which the firearm magazine-interface  20  operates and interfaces with the firearm  10 . 
         [0019]    In  FIGS. 1 and 2 , the firearm  10  is shown with a magazine  6 . The stock firearm magazine-interface (not shown) has been removed and the firearm magazine-interface  20  of improved construction is installed. 
         [0020]    A portion of the firearm  10  is shown in a simplified fashion, as the mechanisms and operations of such a firearm  10  are well known and discussed in the prior art. The firearm  10  has a receiver  18  which includes bolt carrier rails (not visible) for receiving the bolt carrier (not visible) which carries the bolt  14  (see  FIG. 2 ). The trigger and trigger mechanism is not shown for brevity purposes, as it is well known in the industry. 
         [0021]    Attached to the receiver  18  is the barrel  16 . A receiver cross-member pin  12  is used by the firearm magazine-interface  20  to provide a sturdy anchor during the bolt-hold-open action as will be shown later. The firearm magazine-interface  20  is shown with the removably attached magazine  6  inserted. The firearm magazine-interface  20  replaces the stock magazine-interface (not shown) and the firearm magazine-interface  20  is attached to the firearm  10  using the same or similar mounting arrangement as used for the stock magazine-interface. The bolt-hold-open release paddle  44  will be explained later. 
         [0022]    In  FIG. 2 , the bolt  14  (e.g. spring-loaded bolt  14 ) is shown in rearward position, prior to engaging the round  8  into the chamber (see  FIG. 3 ). In a typical operation of the firearm  10 , after a first round  8  is fired, back gases force the spring-loaded bolt carrier (not shown) and bolt  14  back far enough to eject the spent cartridge and allow the next round  8  to lift from the spring-loaded magazine  6 . Once the gas pressure subsides, the spring-loaded bolt  14  is pushed forward by spring pressure and chambers the next round  8 , ready to fire. One problem being solved by the improved firearm magazine-interface  20  is magazine  6  selection. In general, magazines  6  made for one type of firearm  10  (e.g. AK47, AK 74) do not have a mechanism for indicating the last round from the magazine  6  has been fired (e.g. the magazine is empty). Fortunately, other magazines  6  such as those used with, for example, the AR15 or M16 types of firearms have a magazine follower  7  (see  FIGS. 3A and 3B ) designed to interface with a bolt-hold open mechanism of, for example, the AR15 or M16. The magazine follower  7  provides an upward force and feeds the rounds  8  into the magazine opening and eventually into the chamber  15  (see  FIGS. 3A and 3B ). After the last round  8  is chambered from the magazine  6  and the magazine  6  is empty, the follower of such magazines  6  pushes upward by force of the magazine spring  4  (see  FIGS. 3A and 3B ). In such, the magazine follower  7  (see FIGS.  3 A/B) mechanically moves upward as the last round  8  is chambered. Therefore, one feature of the firearm magazine-interface  20  is to adapt such magazines  6  originally intended for a different style firearm to the firearm  10 . A second feature of the firearm magazine-interface  20  is a bolt-hold-open feature. In this, the firearm magazine-interface  20  uses the magazine follower  7  to lock the spring-loaded bolt  14  in the open position after the last round  8  from the magazine  6  is fired. Another feature of the firearm magazine-interface  20  is a quick-release for the magazine  6 , such that, after firing the last round  8  in the magazine  6 , a simple press of magazine release button  30  (see  FIG. 2 ) ejects the empty magazine  6  and the shooter need only insert in a new magazine  6  then press the bolt-hold release paddle  44 . Pressing of the bolt-hold release paddle  44  initiates return of the bolt  14  and the next round  8  from the new magazine  6  is caught by the bolt  14  and chambered, ready to fire. 
         [0023]    Referring to  FIGS. 3A and 3B , side cut-away views along line  3 - 3  of  FIG. 2  are shown. The first view in  FIG. 3A  shows a remaining round  8  in the magazine  6  after firing of the firearm  10 . The rounds  8  are pushed upwardly within the magazine  6  by a magazine spring  4 , as known in the industry. As the spring-loaded bolt  14  moves forward (returns) by spring pressure, it catches an edge of the next round  8 , pushes the round  8  forward, and the round  8  slides up a ramp  19  and into the chamber  15 , ready to fire. As the last round  8  is chambered, the magazine follower  7  of the magazine  6  rises and pushes the bolt-hold lock  24  up as shown in  FIG. 3B . The magazine spring  4  maintains upward pressure on the magazine follower  7 , and, consequently, on the bolt-hold lock  24 . As the spring-loaded bolt  14  is pushed back by gas pressure after the last round  8  is fired, an angled surface  13  on the spring-loaded bolt  14  moves against an angled forward edge  23  (see  FIG. 4 ) on the bolt-hold lock  24 , temporarily pushing the bolt-hold lock  24  out of the way of the returning spring-loaded bolt  14  until the spring-loaded bolt  14  completely passes the bolt-hold lock  24 , at which time the bolt-hold lock  24  is pushed upward by force of the magazine spring  4  pushing upwardly on the magazine follower  7  and upward on the follower catch ledge  50  of the bolt-hold lock  24  (see  FIG. 4 ). The interaction between the spring-loaded bolt  14  and the bolt-hold lock  24  also provides an audible, visual and tactile variation from that provided when rounds  8  are still available in the magazine  6 , thereby providing clear indication to the shooter that they have fired the last round  8  in the magazine  6 . Note that it is preferred that the angled forward edge  23  be an angle similar to that of the leading angled surface  13  of the bolt  14 , though, it is anticipated that other surface shapes  23  will work as well, including curved or rounded surfaces  23 . 
         [0024]    Once the gas pressure subsides, the spring-loaded bolt  14  is urged towards the chamber  15  by spring force to chamber the next round  8 . The spring-loaded bolt  14  has a high amount of force as it is pushed forward under spring pressure. To withstand this force, the bolt-hold lock  24  is supported by the receiver cross-member pin  12 , providing sufficient, rigid structure when the face of the spring-loaded bolt  14  hits the bolt-hold lock  24 . The face of the spring-loaded bolt  14  pushes against the bolt catch edge  54  of the bolt-hold lock  24 , holding the bolt-hold lock up, even after the magazine  6  is removed. Since the bolt-hold lock  24  blocks the movement of the spring-loaded bolt  14 , the spring-loaded bolt  14  remains cocked until a new magazine  6  is inserted, at which time the bolt-hold release paddle  44  is pressed, pulling down the bolt-hold lock  24  and allowing the spring-loaded bolt  14  to move forward, catching the top edge of a first round  8  of the new magazine  6  and pushing the round  8  into the chamber  15 . Note, prior to the firearm magazine-interface  20 , after firing of the last round  8 , the spring-loaded bolt  14  would travel forward to the empty chamber  15 , without any indication the firearm is empty until the subsequent failure to fire at the next trigger pull. Also, after installing a new magazine  6 , the shooter needed to manually pull back the spring-loaded carrier and bolt  14  to chamber the next round  8 . Although many a shooter is very quick at this action, the critical seconds when the firearm  10  is not loaded often means life or death. Furthermore, the location of the bolt-hold release paddle  44  is such that as the shooter inserts a new magazine  6 , the shooter&#39;s thumb is local to the bolt-hold release paddle  44  and pressing of the bolt-hold release paddle  44  is a natural, quick action, taking little extra time above that of inserting the new magazine  6 . 
         [0025]    As shown in the exploded view of the firearm magazine-interface  20  in  FIG. 4 , the firearm magazine-interface  20  includes a magazine frame  22 . A first area  23 / 50 / 54  of the bolt-hold lock has an angled forward edge  23 , a follower contact ledge  50 , and a bolt catch edge  54 . The follower contact ledge  50  interfaces with the magazine follower  7  and, therefore, is lifted when the magazine follower  7  lifts under spring force of the magazine spring  4  when the magazine  6  is empty. Note that the follower contact ledge  50  is shown in the first area  23 / 50 / 54  of the bolt-hold lock  24  but in alternate embodiments is located in different areas of the bolt-hold lock  24  such as in the distal area  53  of the bolt-hold lock  24 . 
         [0026]    Pressure and friction of the face of the spring-loaded bolt  14  pushing against the back surface  54  of the bolt-hold lock  24  holds the bolt-hold lock  24  in the extended position while the empty magazine  6  is removed and a new magazine  6  is inserted. The magazine follower  7  of the new, non-empty, magazine  6  is not being pushed up far enough by the magazine spring  4  as to push on the follower contact ledge  23  and therefore, the bolt-hold lock  24  is no longer biased by the force of the magazine spring  4  but is held in place by pressure and friction from the face of the spring-loaded bolt  14  against the bolt catch edge  54 . A pin  27  pivotally holds the bolt release lever  40  to the frame  22 . While the bolt-hold lock  24  moves up, the bolt-hold lock pin  25  affixed to a distal area  52  of the bolt-hold lock  24  pushes upwardly on the bolt release lever  40 , rotating the bolt release lever  40  around pin  27  and pushing the bolt-hold release paddle  44  in an opposing downward direction with respect to the magazine frame  22 . The bolt-hold release paddle  44  is affixed to the bolt-hold release lever  40  by, for example, pins  46 / 48  or any other fastening arrangement. After the new magazine  6  is inserted, the bolt-hold release paddle  44  is pushed upward by the shooter, pulling the bolt-hold lock pin  25  downward and, hence, pulling the bolt-hold lock  24  downward (retracted position) until the bolt catch edge  54  clears the face of the spring-loaded bolt  14  and the spring-loaded bolt  14  moves forward, catching the top round  8  from the new magazine  6  and pushing the top round  8  into the chamber  15 , ready to fire. A bolt-hold lock return spring  38  keeps the bolt-hold lock  24  biased in the retracted (down with respect to  FIG. 4 ) position so as to prevent the bolt-hold lock  24  from sliding upwardly when there are still rounds  8  in the magazine  6 . 
         [0027]    While there are rounds  8  remaining in the magazine  6 , the bolt-hold lock  24  is biased away from the bolt  14  by the bolt-hold lock return spring  38  and as the bolt  14  is forced away from the chamber  15 . 
         [0028]    After firing of a round  8 , a first distinctive noise is made, full recoil is felt and the bolt carrier charge handle is visibly forward in the lock-up position. After firing of the last round  8  from the magazine  6  (e.g., the magazine  6  is empty), as the bolt  14  is forced away from the chamber  15 , the angled leading edge  13  of the bolt  14  hits the angled forward edge  23  of the bolt-hold lock  24 , making a different, second, distinctive noise, partial recoil is felt, and the bolt carrier charge handle is visibly rearward out of lock-up. The shooter will know when the last round  8  has been fired based upon these differences and can eject the empty magazine  6 , replace the empty magazine  6  with a new magazine  6  and press the bolt-hold release paddle  44  to chamber a first round  8  from the new magazine  6  without having to re-cock the bolt  14 . 
         [0029]    On the opposing side of the frame  22  is a magazine release button  30 . The magazine release button  30  is outwardly spring biased by a magazine catch spring  36  and interfaces to a magazine catch  42  by a magazine catch adjustment spacer  34  with a fastener  32  (e.g. screw  32 ). After the shooter realizes that the last round  8  has been fired, the shooter presses the magazine release button  30  and the magazine catch  42  moves outwardly, thereby releasing the empty magazine  6  which drops out of the magazine frame  22 . 
         [0030]    Equivalent elements can be substituted for the ones set forth above such that they perform in substantially the same manner in substantially the same way for achieving substantially the same result. 
         [0031]    It is believed that the system and method as described and many of its attendant advantages will be understood by the foregoing description. It is also believed that it will be apparent that various changes may be made in the form, construction and arrangement of the components thereof without departing from the scope and spirit of the invention or without sacrificing all of its material advantages. The form herein before described being merely exemplary and explanatory embodiment thereof. It is the intention of the following claims to encompass and include such changes.