Abstract:
Devices and methods of converting semi-automatic firearms to a double-fire mode where a firearm fires a shot upon a single pull of a trigger, and fires a second shot upon a release of the trigger. A clip attachment can be constructed from a single component shaped to fit and mount onto the trigger and extend to protrude between and separate the foot of the safety-sear from the top of the trigger plate affecting the distance between the hammer engaging notch of the safety-sear and the hammer engaging notch of the trigger-sear which allows the firearm to discharge upon release of the trigger. Another version has a spacer pre-built onto a bottom portion of the pivotal safety sear.

Description:
FIELD OF INVENTION 
   This invention relates to firearms, and in particular to retrofit devices and methods and pre-built devices and methods for increasing the firing rate of semi-automatic firearms, such as but not limited to AK type rifles, to a double-fire mode where two shots are fired with a single pull and release of a trigger. 
   BACKGROUND AND PRIOR ART 
   Semi-automatic firearms have a limited firing rate which does not approach the firing rate of automatic firearms. Automatic firearms are also known to be more expensive and harder to acquire than semi-automatic firearms. As a result, many devices have been proposed over the years for increasing the firing rate of semi-automatic firearms. See for example, U.S. Pat. No.: 3,184,875 to Klebe; U.S. Pat. No. 4,344,351 to McQueen; U.S. Pat. No. 4,787,288 to Miller; and U.S. Pat. Nos. 4,803,910 and 5,074,190 both to Troncoso. 
   However, these devices require multiple components and extra tools such as screwdrivers, wrenches and pliers, and the like, that require extra fasteners such as screws, and the like. The prior art converter devices must then be carefully assembled and can take excessive amounts of time for proper assembly in order to work. Some of these converter devices further require extensive modifications such as opening up and/or drilling into the existing firearms that can damage the firearms. Thus, all of these prior art converter devices are generally inconvenient to attach, difficult to operate and control properly, as well as potentially unreliable. Furthermore, once attached these devices can also prevent the firearms from firing at rates other than that which they were meant to operate since the converter attachment can become a fixed addition that is difficult to remove. 
   Still furthermore, the above devices only convert firearms to a full-automatic mode. Full-automatic firearms are generally considered to be a NFA Class 3 firearm that is typically only available to law enforcement, and not to average consumers. 
   Thus, the need exists for solutions to the above problems with the prior art. 
   SUMMARY OF THE INVENTION 
   A primary objective of the invention is to convert firearms to a double-fire mode where two shots can occur after a single pull and single release of a trigger. 
   A second objective of the present invention is to provide an attachment device and method for converting semi-automatic firearms to a double-fire mode that is both easy and convenient to be attached to the trigger. 
   A third objective of the present invention is to provide an attachment device and method for converting semi-automatic firearms to a double-fire mode that is easy to operate and control properly. 
   A fourth objective of the present invention is to provide an attachment device and method for converting semi-automatic firearms to a double-fire mode that would be more reliable than devices that convert to automatic firearms. 
   A fifth objective of the present invention is to provide an attachment device and method for converting semi-automatic firearms to a double-fire mode that can be conveniently attached within a short period of time. 
   A sixth objective of this invention is to provide an attachment device and method for converting semi-automatic firearms to double-fire mode that does not require taking apart, tampering or destroying the existing firearm device. 
   A seventh objective of the present invention is to provide an attachment device and method for converting semi-automatic firearms to a double-fire mode that can be easily removed so that the original semi-automatic firearm can still be operated. 
   An eighth objective of the present invention is to provide an attachment device and method of converting a firearm to a double-fire mode for use by civilians and consumers, that is not an automatic firearm that is restricted to law enforcement. 
   The novel invention allows for a double-fire mode where a firearm fires upon a single pull of a trigger, and fires again upon a single release of the trigger. 
   The novel trigger attachment device and method allows for various rates of fire other than the available semi-automatic and automatic rates of current firearms. The invention provides a simple, reliable attachment which can be quickly and easily attached to the semi-automatic firearm for increasing the firing rate up to a double-fire mode without causing automatic firing of the semi-automatic firearm. 
   The attachment causes the firearm to fire upon release of the trigger by separating the foot of the safety sear from the top of the trigger plate rotating the safety sear rearward on its pivot point which causes an increased gap between the trigger sear, at its hammer engaging notch, and the safety sear, at its hammer engaging notch allowing the hammer to pass through this increased gap upon release of the trigger. 
   The attachment can be constructed from a single component shaped to fit and mount onto the trigger with two tab-like features on either side that bend around to the backside of the trigger to maintain the attachments position on the trigger, and an extended length following the concave contour of the trigger upward where it is bent horizontally along the top surface of the trigger plate and under the bottom of the foot of the safety-sear separating the foot of the safety-sear from the top surface of the trigger plate causing an increased distance between the hammer engaging notch of the safety-sear and the hammer engaging notch of the trigger-sear due to the pivot point and rearward rotation of the safety-sear relative to the trigger-sear. The increased distance between the hammer engaging notch of the safety-sear and the hammer engaging notch of the trigger sear will not be extreme enough to prevent the safety-sear from engaging and retaining the hammer when the trigger is pulled and held, firing and cycling the firearm, yet will be sufficient enough to prevent the hammer engaging notch of the trigger-sear from engaging the hammer when the trigger is released therefore allowing the hammer to pass through and on to the firing pin into the firing position firing and cycling the firearm upon release of the trigger. 
   Another embodiment has the pivotal safety sear of the trigger assembly pre-built and/or preshaped and/or preformed with a footer so that the space between the upper right and left hammer catch notches is enlarged. 
   Further objects and advantages of this invention will be apparent from the following detailed description of the presently preferred embodiments which are illustrated schematically in the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
       FIG. 1  shows a perspective view of a first preferred embodiment of a double fire spacer. 
       FIG. 2  is a front view of the double fire spacer of  FIG. 1  along arrow  2 A. 
       FIG. 3  is a top view of the double fire spacer of  FIG. 1  along arrow  3 A. 
       FIG. 4  is a side view of the double fire spacer of  FIG. 4  along arrow  4 A. 
       FIG. 5  is a perspective view of a prior art type weapon trigger assembly. 
       FIG. 6  is a perspective view of the trigger assembly of  FIG. 5  with the double fire spacer. 
       FIG. 7  is a side cross-sectional view of the trigger assembly of  FIG. 5 . 
       FIG. 8  is a side cross-sectional view of the trigger assembly of  FIG. 7  with the double fire spacer. 
       FIGS. 9 ,  10 ,  11 ,  12 ,  13 ,  14 ,  15  and  16  show the various positions of components of the prior art trigger assembly of  FIGS. 5 and 7  during a firing sequence. 
       FIGS. 17 ,  18 ,  19 ,  20 ,  21 ,  22 ,  23  and  24  show the various positions of the components of a trigger assembly with the novel double fire spacer of  FIGS. 1–4 ,  6  and  8  during a firing sequence. 
       FIG. 25  is a side cross-sectional view of the trigger assembly of  FIG. 7  with a built in spacer. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Before explaining the disclosed embodiments of the present invention in detail it is to be understood that the invention is not limited in its application to the details of the particular arrangement shown since the invention is capable of other embodiments. Also, the terminology used herein is for the purpose of description and not of limitation. 
     FIG. 1  shows a perspective view of a first preferred embodiment of a double fire spacer  1 .  FIG. 2  is a front view of the double fire spacer  1  of  FIG. 1  along arrow  2 A.  FIG. 3  is a top view of the double fire spacer  1  of  FIG. 1  along arrow  3 A.  FIG. 4  is a side view of the double fire spacer  1  of  FIG. 4  along arrow  4 A. 
   Referring to  FIGS. 1–4 , the double fire spacer  1  can be clip having a curved backing member  2  with bent portion  4  having an upper flange member  6 . Extending from lower concave curved portion  8  of the backing member  2  can be clipping end  10  having four protruding bendable tab members  12 ,  14 ,  16 ,  18 , with two tab members on to each side of the clip  1 . The double fire spacer can be formed from a metal, such as but not limited to cold roll steel, stainless steel, galvanized metal, and the like. 
     FIG. 5  is a perspective view of a prior art type weapon trigger assembly  100 .  FIG. 7  is a side cross-sectional view of the trigger assembly  100  of  FIG. 5 . The prior art type weapon trigger assembly  100  is of the type used in semi-automatic firearms, such as AK type firearms, such as but not limited to AK-47 rifles, and the like, that can include trigger  110  having concave curved surface  112  that engages a finger of a user and opposite convex curved surface  114 . Along a top portion of the trigger  110  can be a mounting plate  120 , with a J-shaped trigger sear plate  150  vertically extending up and fixably attached along one side of the mounting plate  120 . The J-shaped trigger sear plate has a fixed located primary hammer latch portion  152  (a left upper hammer engage notch). Pivotally attached to a side wall portion of the trigger sear plate  150  at pivot point  145  can be a J-shaped safety sear plate  140  having secondary hammer latch portion  142  (a right upper hammer engage notch). 
   Referring to  FIGS. 5 and 7  prior art trigger assembly  100  can include a secondary latch return spring  130  that rests in an expanded open condition can be attached to a rear bottom portion  144  of safety sear plate safety sear plate  140  and to the mounting plate  120 . The front bottom portion  146  of the safety sear plate  140  forms a stop point when resting on the mounting plate  120  which sets the resting window opening space at a distance D 1  between upper right hammer engage notch  142  and the upper left hammer engage notch  152 . 
     FIG. 6  is a perspective view of the trigger assembly  100  of  FIG. 5  with the double fire spacer  1  in an assembled view  100 ′.  FIG. 8  is a side cross-sectional view of the trigger assembly  100  of  FIG. 7  with the double fire spacer  1  in the assembled view  100 ′. The double fire spacer  1  can clip onto the assembly  100  having the curved portion  8  of backing member  2  to abut against the concave curved finger pulling surface  112  of the trigger  110  with ends of the tab members  12 ,  14 ,  16 ,  18  bent in the direction of arrow BE about the convex curved surface  114  of the trigger  110 . When attached the upper flange member  6  of the spacer  1  rests on top of an edge surface of the mounting plate  120  raising the front bottom portion  146  of the safety sear plate  140  and pivotally moving back the upper right hammer engage notch  142  of the safety sear plate  140  in the direction of arrow BB. The flange member  6  effectively increases the resting window opening space to a distance D 2  (where D 2  is greater than D 1 ) between the upper right hammer engage notch  142  and the upper left hammer engage notch  152 . 
     FIGS. 9 ,  10 ,  11 ,  12 ,  13 ,  14 ,  15  and  16  show the various positions of components of the prior art trigger assembly of  FIGS. 5 and 7  during a normal firing sequence. The normal firing sequence of the trigger assembly will now be described. 
     FIG. 9  is a side view of the trigger assembly  100  in the firearm, such as a semi-automatic rifle in a ready to fire position with a hammer head  161  on a pivotal hammer  160  located in space D 1  between primary hammer latch  152  and secondary hammer latch  142 . In this view an ammo clip  190  is positioned within the firearm below a spring loaded slide  170  having a firing pin  180  therethrough, and a round  192  (bullet) located in a chamber of the firearm. 
     FIG. 10  is a next sequence view of  FIG. 9  showing the trigger  110  depressed by a finger F in the direction of arrow P, the hammer  160  released and being pulled by coil spring  167  so that a surface portion  163  engages and end of the firing pin  180  causing an opposite end to strike the bullet  192  in the chamber, and a round detonated so that a slug  196  exits the firearm chamber in the direction of arrow FR leaving behind a shell  194 . A stop  169  prevents the hammer that pivots from point  165  from traveling further than necessary to strike the firing pin  180 . Here, the trigger assembly  100  rotates in the direction of arrow P 1  forward allowing the hammer head  161  to be released from the primary hammer head latch portion  152 . 
     FIG. 11  is a next sequence view of  FIG. 10  showing the trigger  110  still being held, the slide  170  propelled back in the direction of arrow SL 1  by detonation, which moves the hammer  160  back and the shell  194  ejecting from the firearm chamber. 
     FIG. 12  is a next sequence view of  FIG. 11  showing the trigger  110  still being held back by the finger F, the hammer head  161 ,  162  now caught by the secondary latch  142 , and a new round  198  being moved into a loading position. The secondary latch  142  catches an edge  162  of the hammer head  161  keeping the hammer  160  from cycling back while the finger F is still in the pulled back position. 
     FIG. 13  is a next sequence view of  FIG. 12  showing the trigger  110  still being held and the slide  170  returning back to the initial position in the direction of arrow SL 2  based on being spring biased. 
     FIG. 14  is a next sequence view of  FIG. 13  showing the trigger  110  still being held and the slide  170  having returned to the fire position having moved the new round  198  to a ready to fire position. 
     FIG. 15  is a next sequence view of  FIG. 14  showing the trigger  110  being released by the finger moving away in the direction of arrow RI, where the edges  162  on the hammer head  161  slips from the secondary latch  142  and is caught by the primary latch  152 . Here, the trigger assembly  100  rotates backward in the direction of arrow P 2  (opposite the direction P 1  shown in  FIG. 10 ). 
     FIG. 16  is a next sequence view of  FIG. 15  showing the trigger assembly  100  in a ready to fire position similar to that previously shown in  FIG. 9 . 
   During the sequence views of  FIGS. 9–16 , the firearm fires a single shot from the result of a single action of pulling the trigger  110  back once and allowing the trigger  110  to return to the ready to fire position. 
     FIGS. 17 ,  18 ,  19 ,  20 ,  21 ,  22 ,  23  and  24  show the various positions of the components of the trigger assembly  100  of the prior art modified with the novel double fire spacer  1  of  FIGS. 1–4 ,  6  and  8  during a firing sequence. 
     FIG. 17  is another view of  FIG. 9  showing a side view of the modified trigger assembly  100 ′ with the novel double fire spacer  1  attached to thereto with the firearm in a ready to fire position. As shown the space D 2  between the secondary hammer latch portion  142  and the primary hammer latch portion  152  is larger than the space D 1  shown in  FIG. 9  without the novel spacer  1 . For example, a firearm having a space D 1  being approximately 4/10 of an inch wide, can be increased by the clip spacer  1 . For example, a flange member  6  having a thickness of approximately 1/16 of an inch thick can increase the space opening D 1  from approximately 4/10 of an inch to a larger space opening D 2  having a width of approximately 9/20 of an inch. As previously described in reference to  FIGS. 6 and 8 , the flange member  6  of the novel spacer  1  effectively increases the resting window opening space to a distance D 2  (where D 2  is greater than D 1 ) between the upper right hammer engage notch  142  and the upper left hammer engage notch  152 . 
     FIG. 18  is a next sequence view of  FIG. 17  showing the trigger  110  depressed by finger F, the hammer  160  released and the round detonated by the firing pin in the slider  170  so that a slug  196  leaves a shell  194  behind, functioning similar to  FIG. 10 . 
     FIG. 19  is a next sequence view of  FIG. 18  showing the trigger  110  in the modified trigger assembly  100 ′ still being held, the slide  170  propelled back in the direction by arrow SL 1  by the firing detonation, and the hammer  160  moving back, and the shell  194  ejecting out similar to  FIG. 11 . 
     FIG. 20  is a next sequence view of  FIG. 19  showing the trigger  110  still being held back, the head  161  of the hammer  160  caught by secondary latch  142 , and a new round moved into a loading position similar to that of  FIG. 12 . 
     FIG. 21  is a next sequence view of  FIG. 20  showing the trigger  110  held, spring biased slide  170  returning in the direction of arrow SL 2  to a fire position similar to that shown in  FIG. 13 . 
     FIG. 22  is a next sequence view of  FIG. 21  showing the trigger held back and the slide  170  returned. At this point the function of the components in the trigger assembly  100 ′ starts the novel double fire mode in the firearm. 
     FIG. 23  is a next sequence view of  FIG. 22  showing the trigger  110  releasing, and the hammer head  161 ,  162  slipping prematurely from the secondary latch  142  (because of the enlarged space D 2 ), causing the hammer to rotate in the direction of arrow DHR hitting the firing pin  180  moving the slider  170  against the next round  198 ′. Unlike, the prior art sequence view shown in  FIG. 15 , the enlarged space D 2  causes the hammer head to slip and NOT be caught by the primary hammer latch portion  152  (the left upper engage notch). The modified trigger assembly  100 ′ causes a double fire mode (two shots in sequence) by a single trigger pull and release action. Immediately after the double fire shot, the slider  170  is caused to move back moving the hammer  160  back (similar to that shown in  FIGS. 11 ,  12 ,  19 ,  20 . The slide  170  will cycle through loading sequence again. The invention allows for a quick double fire action by a single trigger pull and release action. 
     FIG. 24  shows the final sequence of the double fire mode showing the trigger  110  released, the slide  170  cycled, and the firearm in a ready to fire position, and the firearm components in positions similar to that shown in  FIG. 17 . 
     FIG. 25  is a side cross-sectional view of another embodiment  200  having the trigger assembly  100  of  FIG. 7  with a built in spacer to affect the enlarged window space opening D 2 . Here, the trigger assembly  200  has a trigger  110 , mounting plate  120 , trigger sear plate  150  with primary hammer latch portion  152 , and modified pivotal safety sear plate  140  having secondary hammer latch portion  142 , front bottom  146 , and a pre-formed (for example pre-molded, and the like) downwardly protruding footer spacer  248 , which effects the enlarged window space opening D 2 . The secondary embodiment  200  can function similar to the clip spacer  1  previously described, and effect a double fire mode action every time a trigger is pulled once. 
   The invention can include additional features as desired, such as but not limited to a resilient pad surface that can be added to the curved external finger engaging surface of the clip spacer  1  for comfort and enhanced gripping action by the user. 
   While the invention has been described, disclosed, illustrated and shown in various terms of certain embodiments or modifications which it has presumed in practice, the scope of the invention is not intended to be, nor should it be deemed to be, limited thereby and such other modifications or embodiments as may be suggested by the teachings herein are particularly reserved especially as they fall within the breadth and scope of the claims here appended.