Abstract:
The invention is designed to be fitted into the AK47-type semiautomatic firearms to provide a missing but vital feature of locking the reciprocating bolt assembly of said firearm after having chambered, fired and ejected the last cartridge from its removable magazine. The invention is designed to be installed into the receiver portion of the firearm as well as incorporating a modification into the removable magazine housing and follower. The invention consists of a number of components that will work in cooperation with each other to provide the above desired feature.

Description:
BACKGROUND OF INVENTION  
       [0001]     The AK47-type firearms have a number of weaknesses. On of these is the lack of a bolt stop or bolt catch feature that prevents the bolt and the bolt carrier assembly from moving forward to battery upon firing and ejecting the last round from the ammunition feeding device or magazine. This shortcoming often leads to the users unanticipated running out of ammunition unless the user counts the number of bullets fired from the magazine. In most cases, this results in a dry fire, where the trigger is pulled on an empty chamber. This slows down the operators response time to refresh the firearms magazine.  
         [0002]     The unmodified rifle and its operation is fully described in a publication entitled The AK-47 Assault Rifle edited by Wyant La Mont (Normount Technical Publications, Wickenburg, Ariz., Copyright 1969 by Donald B. Mclean). This type of rifle is also described in the World patent NO. WO9905467. Therefore, its operation will not be described in detail here.  
         [0003]     What is needed is a mechanism that can easily be added on a (AK47-type) firearm, which prevents the bolt carrier from moving forward upon firing/ejecting of the last round of ammunition and which provides a signal to the user to warn him/her that he/she has run out of ammunition.  
       SUMMARY OF INVENTION  
       [0004]     Although this invention is described in conjunction with AK47-type firearms, other types of firearms may benefit from the present invention, and are not meant to be excluded from the scope of the present invention. AK47-type firearms include, but are not limited to, the AKM, MAK-90, MAADI and Krinkov series firearms. These firearms commonly have a stamped steel (or machined steel) receiver body, a removable single (or double) stack stamped steel (or molded plastic box magazine) with stamped steel (or molded plastic) magazine follower, and semi-automatic (or automatic) rate fire capability.  
         [0005]     A mechanism in accordance with this invention automatically locks the bolt carrier in the semi-rearward position after having chambered, fired and ejected the last round from the magazine. This invention also allows the user to manually lock the bolt carrier in the semi-rearward position by use of a thumb release, and manually release the locked bolt carrier from the semi-rearward position to battery by the thumb release, with or without an empty or charged magazine installed in the receiver. Further, upon having locked the bolt carrier semi-rearward by the use of this invention, it also allows the magazine to be removed and replaced without releasing the bolt carrier. Furthermore, this invention allows the release of the bolt carrier when a fully charged magazine is installed, by pulling on the charging handle of the bolt carrier rearward until the bolt catch (or bolt stop) is disengaged. This allows the bolt carrier to move forward to battery, stripping a bullet from the magazine and chambering it. Also, this invention allows the manual release of the bolt carrier either with the thumb release or the bolt carrier charging handle when there is no magazine installed, allowing the bolt carrier to move forward to battery.  
         [0006]     The invention, therefore, provides a visual indication of the last cartridge fired by keeping the bolt carrier in the open or semi-rearward position, provides for quicker removal of empty magazine and installation of a fresh magazine, and allows quicker charging of the firearm by the use of an external thumb release. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0007]      FIG. 1 . is a right elevation cut away of the receiver portion of the firearm showing the basic components of the present invention, the firing mechanism cocked and ready for firing the bolt catch mechanism in the retracted state, with magazine not installed.  
         [0008]      FIG. 2  is the exploded isometric view of  FIG. 1 , showing the relationship of the bolt catch mechanism components with the firearm components and receiver. Magazine displaced from the receiver.  
         [0009]      FIG. 3 . is the isometric view of a preferred embodiment of the present invention, shown separately from the firearm for added clarity. Receiver and fire control components are not shown.  
         [0010]      FIG. 4 . is the left elevation cutaway of the firearm showing the bolt catch mechanism in the retracted position with fully charged magazine installed. Firing mechanism components have been omitted for clarity, left wall removed, bolt carrier moving past the catch lever.  
         [0011]      FIG. 5 . is the left elevation cutaway of the firearm showing the bolt catch mechanism in the elevated or engaged position with empty magazine installed. Left wall and firing mechanism components have been omitted for clarity. 
     
    
     DETAILED DESCRIPTION  
       [0012]     Referring to  FIGS. 1, 2 , the rifle includes a channel-shaped receiver  1  having a bottom wall  30 , left wall  2 , and right wall  3  and a rear block  25 . Longitudinally sliding in the upper portion of the receiver  1  is a bolt carrier  13  (or slide), which is supported by means of flanges  12 ,  18  projecting from the inner surfaces of the side walls. The receiver walls  1 ,  3  are also connected by means of a semi-permanent solid rivet  9 . The trigger assembly includes a trigger  24  pivotally mounted to the receiver  1  by means of a removable pin  35  and having the usual projection for engagement by the trigger finger of an operator. A gas operated piston (not shown) of the bolt carrier  13  to move the latter rearward immediately upon firing of a cartridge. A spiral return spring  29  returns the carrier assembly to its forward locked position after firing. The removable box magazine is comprised of the housing  5 , in which is housed the magazine follower  4  which is constrained to move in the vertical direction by means of the inside envelope of the magazine housing  5 . The magazine follower  4  is acted upon by an internal wire spring (not shown) also housed within the magazine housing  5 . The magazine spring is constrained within the magazine by a removable magazine floor plate (not shown).  
         [0013]     In a preferred embodiment, the invention is comprised of six major components as shown in  FIG. 2, 3 . These are: the magazine follower  4 , the magazine tab  26 , sensor lever  19 , catch lever  22 , catch lever head  23 , the return spring  8 .  
         [0014]     The sensor lever  19  with integral sensor tab  31 , integral thumb release  32  protruding through the bottom of the receiver  1  in the area of the magazine well  27 , pivotally mounted on a pin  21 . The pin  21  is securely fastened to the inside left wall  2  of the receiver  3 . The bolt catch lever  22  is pivotally mounted on the solid rivet  9 , connecting the walls  2 ,  3  of the firearm. A catch return spring  8  which imparts a continuous counterclockwise torque (when viewed in  FIG. 1 ) on the catch lever  22 , to prevent the catch lever  22  from rotating unless acted upon by the sensor lever  19 . The magazine follower  4  is equipped with a tab  26 , that remains retracted within the magazine housing until the last cartridge is fed into the chamber at which point the tab  26  rises through a longitudinal slot  34  in the top of the magazine housing  5 . The sensor lever  19  and the catch lever  22  interact with each other via two sets of pins  14 ,  15  in the catch lever  22  and corresponding set of holes  16 ,  17  in the sensor lever  19 .  
         [0015]     Upon imparting a clockwise rotation (when viewed in figures  3 ,  4 ,  5 ) on the sensor lever  19 , rotating about pin  21 , lever  19  engages the catch lever  22  through the interaction of the hole  16  in the sensor lever  19  and the corresponding pin  14  in the catch lever  22 . This interaction results in the counter clockwise rotation of the catch lever  22 , about the receiver rivet  9 , on which it is mounted. In this condition the catch lever  22  is ready to engage the carrier  13 .  
         [0016]     The sensor lever  19  further engages the catch lever  22  through the interaction of a second hole  17  and a corresponding pin  15  in the catch lever  22 . However, this set of hole  17  and pin  15  only engage each other when a counter clockwise rotation (when viewed in  FIGS. 3, 4 ,  5 ) is imparted to the sensor lever  19 , thereby imparting a clockwise rotation on the catch lever  22  about the receiver rivet  9  on which it is mounted. The resulting motion allows for the release of the stopped carrier  13 . The pins  14 ,  15  are located in the catch lever  22  such that they do not ever simultaneously engage their respective holes  16 ,  17  in the sensor lever  19 .  
       Locking the Bolt Carrier in the Semi-Rearward Position After Having Fired the Last Cartridge  
       [0017]     The description of operation will assume that a charged magazine has been installed into the firearm. After having fired and ejected the second to last cartridge, the carrier  13  moves forward under the action of the return spring  29  to chamber the last cartridge, at which point the magazine follower tab  26  also protrudes up through the magazine housing  5  by means of slot  34 , imparting a clockwise rotation (when viewed in  FIGS. 3, 4 ,  5 ) on the sensor lever  19  pivotally mounted about pin  21 , which in turn imparts a counter clockwise rotation of the catch lever  22  pivotally mounted on the receiver rivet  9 , by way of the sensor hole  16  and catch pin  14 . This presents the head  23  of the catch lever  22  in the path of the carrier  13  but is restricted from further motion by the presence of the upper flange  12  projecting from the inner surface of the receiver wall  2 . Upon firing a cartridge the carrier  13 , by action of the chamber gases on the gas piston (not shown) of the carrier  13 , moves longitudinally rearward, overriding the head  23  of the catch lever  22  and impacting the rear block  25  of the receiver  1 . Under the action of the main spring  29  of the firearm, the bolt carrier  13  starts its forward motion. The head  23  of the catch lever  22 , having been returned by to the upper flange  12  the spring forces of the magazine, inhibits the forward motion of the carrier  13  at the carrier notch  33 , effectively locking the bolt carrier  13  in the semi-rearward position.  
       Releasing the Bolt Carrier from the Semi-rearward Position, After Having Installed a Charged Magazine, Using the External Thumb Release  
       [0018]     As the magazine spring (not shown) is compressed under the installation of cartridges within the magazine housing  5 , the magazine follower  4  and tab  26  attached thereon, are retracted into the housing  5 . Upon installing a fully charged magazine into the firearms magazine well  27 , the magazine follower tab  26  no longer impinges on the sensor lever  19 . The absence of the magazine follower tab  26  allows for the return spring  8  to tend to impart a clockwise rotation (when viewed in  FIGS. 3, 4 ,  5 ) of the catch lever  22  about the receiver rivet  9  on which it rotates. Due to friction forces between the head  23  of the catch lever  22  and the notch  33  of the bolt carrier  13 , the carrier  13  remains in the semi-rearward locked position. Upon manually imparting a counter clockwise rotation on the thumb release  32  protruding through the magazine well  27 , a clockwise torque is applied to the catch lever  22  through the sensor hole  17  and corresponding catch lever pin  15 . Enough force is applied to the thumb release  32  and sensor lever  19  to overcome the friction forces between the head  23  of the catch lever  22  and the carrier  13 . Upon rotating the catch lever  22  out of the way of the carrier  13 , the carrier  13  is allowed to move forward under the force of the main spring  29 . As the carrier  13  moves forward to battery, the bolt face (not shown) impacts the next cartridge  10  presented by the magazine and chambers it.  
       Releasing the Bolt Carrier From the Semi-Rearward Locked Position Using the Carrier integral Charging Handle  
       [0019]     Upon having removed the empty magazine, or having installed a fully charged magazine, the magazine follower tab  26  no longer impinges on the sensor lever  19 . The absence of the magazine follower tab  26  allows for the catch lever  22  return spring  8  to tend to impart a clockwise rotation (when viewed in  FIGS. 3, 4 ,  5 ) on the catch lever  22  about the receiver rivet  9  on which it rotates. Due to friction forces between the catch lever  22  head  23  and bolt carrier notch  33 , the bolt carrier  13  remains in the semi-rearward locked position. The carrier may be released from this semi-rearward locked position by use of the carrier charging handle  28 . As the charging handle  28  is manually moved rearward, the clockwise torsion applied by the catch return spring  8  onto the catch lever  22 , allows the catch lever  22  to be retracted as soon as the friction forces are removed by the separation of the carrier  13  and the head  23  of the catch lever  22 . Releasing the charging handle  28  allows the bolt carrier  13  to rapidly move forward under the force of the return spring  29  and locking the bolt within the breach.