Patent Publication Number: US-8112928-B2

Title: Trigger-controlled select fire for M-16 rifle

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present invention claims priority to a U.S. provisional patent application Ser. No. 61/113,731 entitled TRIGGER-CONTROLLED SELECT FIRE FOR AN M-16 RIFLE filed on Nov. 12, 2008, disclosure of which is incorporated herein at least by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is in the field of firearms and pertains particularly to methods and apparatus for enabling a trigger mechanism to switch firing modes from semi-automatic to full automatic under variable applied pressure to the trigger component of the mechanism, the pressure resulting in a change in position of the trigger. 
     2. Discussion of the State of the Art 
     In the field of firearms there are rifles manufactured for military use. A good example of such a rifle is an M-16 rifle. The M-16 rifle is a military weapon that typically has three firing modes governed by a safety selector, the three modes including a safety mode, a semi-automatic mode, and a fully automatic mode. The safety selector mechanism built into the wall of the lower receiver unit and integral to the trigger system is set manually by an operator of the weapon. 
     In safety mode the rifle will not fire. In semi-automatic mode a hammer is released and strikes a firing pin when a user pulls the trigger. Expanding gas from the barrel drives a retraction bolt backward against a spring, resulting in ejection of the spent shell casing and loading of a new shell. The retraction bolt causes the hammer to rotate back into trigger position where it is automatically latched by the disconnector until the trigger returns to full forward, so a second shot cannot be fired while the trigger is still being pulled. When the trigger returns forward the disconnector is released and the hammer rests on the forward end of the trigger. A notch provided in the hammer seats against the trigger and the disconnector moves back and is no longer latching the hammer. The trigger mechanism is then ready to release the hammer to fire a next shot. It has occurred to the inventor that switching from semi-automatic to fully automatic mode for an M-16 and like rifles need not be solely a manual process. Therefore, what is clearly needed is a pressure activated trigger mechanism that enables mode selection between semi-auto and full auto through the application of pressure on the trigger, changing position of the trigger. 
     SUMMARY OF THE INVENTION 
     A problem stated above is that while it is desired to be able to fire continuously using automatic fire on a military weapon, conventional means for selecting automatic fire requires adjustment of a safety selector switch on the rifle. 
     Therefore the inventor searched components of trigger systems looking for components that exhibit potential to be modified to enable variable modes of firing without changing firing settings. 
     It occurred to the inventor during an inventive moment that if continuous automatic fire could be enabled in a military rifle without manually setting the mode of fire, then the weapon could be fired more efficiently. 
     Therefore, the inventor created a full auto rocker mechanism and integrated the mechanism with a conventional trigger system creating a unique trigger system, the rocker mechanism enabling full continuous automatic firing of the weapon while the weapon is set in semiautomatic firing mode via the safety selector. 
     Accordingly, in one embodiment of the present invention a trigger system for a firearm including an enclosure having a bottom surface, a trigger pivoted at a first pivot axis within the enclosure, the trigger having a finger extension through the enclosure bottom surface, such that a user may rotate the trigger rocker clockwise around the first pivot axis by pressure on the finger extension, a firing hammer pivoted at a second pivot axis within the receiver volume, forward from the first pivot axis, the firing hammer spring-loaded to rotate clockwise to fire, the firing hammer having a first notch, a disconnector pivoted at the first pivot axis, the disconnector rocker having a hook for engaging the first notch in the firing hammer, which when engaged prevents the firing hammer from rotating clockwise to fire, and a full auto rocker pivoted at a third pivot axis through the trigger, the full auto rocker having a first portion extending downward and forward from the third pivot axis and a second portion extending rearward from the third pivot axis, a part of the second portion overlying a contact point on the disconnector to the rear of the first pivot axis. 
     With a safety selector positioned in semiautomatic fire mode, rotation of the trigger clockwise to a first position, through a first angle, causes the forward, downward extending portion of the full auto rocker to contact the bottom surface of the enclosure, and further clockwise rotation of the trigger rocker beyond the first position causes the full auto rocker to rotate counterclockwise about the third pivot axis, which causes the rearward portion of the full auto rocker to urge downward on the disconnector rocker at the contact point, rotating the disconnector rocker also counterclockwise, leaving the firing hammer unrestrained to fire repeatedly in full automatic mode. 
     In one embodiment the trigger comprises a front edge engaging a second notch in the firing hammer with the firing hammer fully cocked counterclockwise, and the finger extension of the trigger fully forward, thereby holding the firing hammer fully cocked. In one embodiment the trigger system further comprises a safety selector having three selectable positions one of safety, preventing the firing hammer from rotating to fire, semiautomatic, allowing the weapon to fire in that mode and in select fire full automatic depending on variable trigger position, and full automatic mode allowing the weapon to be fired only in that mode. 
     In a preferred embodiment the third pivot axis through the trigger and the full auto rocker is a pin provided through an opening provided in the trigger and openings in the rocker. In one embodiment the safety selector is modified through provision of a relief slot to prevent obstruction of full automatic firing while the safety is set in semiautomatic mode. In a preferred embodiment the rocker is forced into a counterclockwise rotation about the coupling when added pressure is applied to the trigger due to the position of and cam shape of the rocker ends. 
     In one embodiment the trigger system is installed in the lower receiver of an M-16 or AR-15 rifle. 
     According to another aspect of the invention a full auto rocker is provided integrated to a trigger system, the full auto rocker comprising a pair of rocker arms of a like profile and length bridged by a wall at one end and extending away from the wall in substantially parallel alignment, the rocker arms sloping downward and culminating at open cam-shaped ends, and a pair of openings placed horizontally through the rocker arms at a location proximal to the cam-shaped ends. The openings provide a pin path for coupling the rocker mechanism to a trigger of the trigger system forming a pivot point for the full auto rocker, the trigger modified with an opening for accepting a pin. 
     In one embodiment the trigger is pinned between the rocker arms and the full auto rocker is fabricated from stainless steel. In a preferred embodiment, the cam-shaped ends make contact with a bottom surface of a trigger compartment housing the trigger system when a trigger of the trigger system is pulled past a semiautomatic firing position. 
     In the above embodiment the applied force to the trigger beyond the initial contact made urges the rocker mechanism to rotate counter clockwise about the pivot point the direction of rotation directed by the cam shape of the ends of the rocker arms. Further to this embodiment, the forced rotation causes the bridged end of the rocker mechanism to make contact with a disconnector of the trigger system preventing it from engaging a hammer of the trigger system. 
     According to another aspect of the present invention a method is provided for controlling the transition from semiautomatic fire to full automatic fire and back to semiautomatic fire in a trigger system enhanced with a full auto rocker, the trigger system set to semiautomatic firing mode via a safety selector integral to the trigger system comprising the steps (a) pulling a trigger of the trigger system to a first position through a first angle until a single shot is fired in semiautomatic mode, (b) pulling the trigger further toward a second position through a second angle causing the full auto rocker to make contact with a bottom surface of the trigger enclosure and to rotate counterclockwise about a pivot point, (c) pulling the trigger further toward the second position until the full auto rocker makes contact with a disconnector causing it to disengage from the hammer initiating full automatic firing, (d) releasing the trigger to engage the disconnector to the hammer stopping full automatic firing, and (e) releasing the trigger to the maximally forward position to latch the hammer to the trigger allowing the disconnector to disengage from the hammer. 
     In a preferred aspect of the method the safety selector is slotted for part relief. In one aspect in step (a) the hammer of the trigger system is released by the trigger of the trigger system to fire the single shot. In this aspect in step (b) the disconnector is engaged to the hammer. In a preferred aspect in step (c) the hammer remains unrestrained as long as the position of the trigger is maintained. 
     In one aspect of the method in step (d) full auto firing may be re-initiated without releasing the trigger to the forward position by again pulling the trigger toward the second position until the disconnector is again disengaged from the hammer. In one aspect in step (e) the safety selector may be moved to safety or full automatic fire. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         FIG. 1  is an elevation view of a trigger system for an M-16 according to current art. 
         FIG. 2  is an elevation view of an M-16 trigger compartment  100  with a portion thereof broken away to expose a trigger system  101  according to an embodiment of the present invention. 
         FIG. 3  is an elevation view of the full auto rocker of  FIG. 1  according to an embodiment of the present invention. 
         FIG. 4  is an overhead view of the full auto rocker of  FIG. 2 . 
         FIG. 5  is an end view of the full auto rocker of  FIG. 2 . 
         FIG. 6  is an elevation view of a safety selector switch modified to practice the invention. 
         FIG. 7  is a left-end view of the safety selector of  FIG. 5 . 
         FIG. 8  is a process flow chart illustrating steps  700  for practicing full automatic fire from semi-automatic mode according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The inventors provide a trigger system for a military rifle, such as an M-16 or AR-15 for example, that is adapted to be switched from semiautomatic fire to full automatic fire without manually changing position of a safety selector. The invention is described in enabling detail in the following examples, which may represent more than one embodiment of the invention. 
       FIG. 1  is an elevation view of a trigger system  10  for an M-16 according to current art. Trigger system  10  is a grouping of components that together form a trigger mechanism for a standard issue M-16 or an AR-15 style military rifle. As described further above the trigger system is adapted to be controlled by a safety selector, which enables two modes of fire, semiautomatic and automatic, sometimes referred to as select fire in the art. 
     Trigger system  10  includes a trigger  11  and a disconnector  14 . Trigger  11  and disconnector  14  are pivotally mounted on a common axis in a trigger compartment of the lower receiver (not illustrated). One with skill in the art of military weapons will recognize the term lower receiver as the detachable lower stock portion of the weapon containing the trigger system. 
     Trigger  11  and disconnector  14  are pivotally mounted at a pivot axis  16 . Trigger  11  is spring-loaded to assume a first forward position where no firing can occur. The safety selector (not illustrated here) enables the trigger to be locked in the forward or safety position. In this position the weapon cannot be fired. Disconnector  14  is spring-loaded clockwise from the trigger via a coil spring  17 . Hammer  12  is illustrated in this example and is pivotally mounted at a pivot point  15 . Hammer  12  is spring-loaded to pivot in the clockwise direction of the circular arrow associated with pivot point  15 . A full auto sear  13  is illustrated in this example and enables full automatic fire when the safety selector is set in full auto position only. Other springs, pins, retainers, and like hardware known in a trigger system are not illustrated in this example but may be assumed present where required. 
     In conventional operation as known to persons skilled in the art, when the trigger is maximally forward, hammer  12  is prevented from pivoting about pivot point  15  by a notch  18  that rests on the forward end of trigger  11 . At this position disconnector  14  is not latching hammer  12 . To fire, the movement of trigger  11  (pull back) from the forward position releases hammer  12  to pivot clockwise thus firing a single shot (semiautomatic mode). 
     The retraction bolt (not illustrated) forces the hammer to pivot back around to a position where disconnector  14  latches it until the trigger is released and moves back to forward position. Disconnector  14  is urged forward when the trigger is pulled according to the clockwise direction of the arrow associated with pivot point  16 . Therefore, disconnector  14  is in a position to catch the recoiling hammer after the shot is fired and before the trigger is released to prepare for a next shot. 
       FIG. 2  is an elevation view of an M-16 trigger compartment  100  with a portion thereof broken away to expose a trigger system  101  according to an embodiment of the present invention. Trigger compartment  100  is a standard receiver for housing a trigger system and other related mechanical components of a rifle. A portion of trigger compartment  100  is broken away to expose trigger system  101  illustrating the basic trigger components used to fire the rifle. 
     Trigger system  101  is illustrated in this example and is assembled in character of a standard M-16 rifle. The example of an M-16 is used here but it should be noted that the application of the invention is not limited to a specific rifle or trigger system. 
     Trigger system  101  includes a trigger  102  accessible to an operator through a trigger well in the lower receiver. Trigger  102  is typically manufactured of a durable metal like steel and retains the machined shape of a conventional trigger. A conventional trigger may be used with a slight modification of the trigger by placing an opening  107  through the trigger body at a strategic location forward of the standard pivot point  107  shared by the trigger and disconnector  104  of the trigger. Disconnector  104  is analogous to disconnector  14  described above and is not necessarily modified in order to practice the present invention. 
     Trigger system  101  includes a hammer  103 . Hammer  103  may be a conventional steel hammer including the contouring and notching required for normal hammer operation within the trigger system. Hammer  103  is analogous to hammer  12  of  FIG. 1  and does not necessarily require modification in order to practice the present invention. Trigger system  101  includes disconnector  104  that is partially visible in this example. Disconnector  104  is a conventional disconnector for latching and releasing the hammer as described further above. When trigger  102  is in the full forward position (not being pulled) the disconnector has no contact with the hammer. The trigger prevents the hammer from releasing at this point. 
     In some embodiments a safety selector (not illustrated here) may be mounted through the wall of the trigger well in the vicinity of the trigger system. More about the safety selector and how it may be modified to practice the invention is provided further below. A standard full auto sear  109  is illustrated within trigger system  101  and is adapted to enable full automatic firing with the safety selector set to full auto mode. Full auto sear  109  is analogous to full auto sear  13  described further above and does not require modification in order to practice the present invention. 
     Trigger system  101  may be assumed to include all of the necessary mounting hardware, springs, and pins required and known in the art enabling the assembly to perform within the lower receiver. Trigger system  101  further includes a novel component termed a full auto rocker by the inventor, and illustrated herein as a full auto rocker  106 . Full auto rocker  106  is illustrated in trigger system  101  in section line to visually separate it more clearly from the other components. Full auto rocker  106  is illustrated in elevation within trigger system  101  and is pivotally mounted to trigger  102  at pivot axis  107  to form a pivot point for the full auto rocker. 
     It is not visible in elevation view, however full auto rocker  106  has two sides separated by a bridge element that overlies a portion of the disconnector. Full auto rocker  106  is therefore mounted at axis  107  on both sides of the trigger. It is noted herein that the full auto rocker is mounted to the trigger, so the pivot axis only applies only to the full auto rocker. In a preferred embodiment full auto rocker  106  is fabricated of durable steel. In some embodiments the full auto rocker is spring-loaded clockwise. 
     Without full auto rocker  106 , firing is accomplished in the standard manner. With the safety on, the trigger is locked in forward position and no firing is possible. With the safety switched to semi-automatic firing mode, trigger  102  may be pulled back to fire one shot at a time. The trigger must be pulled back and then released before a next shot can occur each time a shot is fired in semi-auto mode. The safety selector must be switched to full auto firing mode before automatic fire can occur by pulling the trigger and maintaining the trigger position to continue firing. 
     In embodiments of the present invention full auto rocker  106  enables full automatic fire while the rifle is in semiautomatic firing mode as dictated by the safety selector. The full auto rocker is an elongate piece a shown having two sides with identical cam-shaped ends disposed at a downward angle. At one point in trigger movement, since the full auto rocker is pivoted to the trigger forward of the trigger pivot axis, the cam ends of the full auto rocker will strike the bottom of the receiver well at point  105 . Moving the trigger past this position forces the cam-shaped rocker ends of full auto rocker downward against the bottom surface of the trigger system compartment above the trigger well, and causes the full auto rocker to rotate counterclockwise about axis  107 . 
     The contact and subsequent force applied, causing counterclockwise rotation of the full auto rocker urges the bridge end of full auto rocker  106  down against disconnector  104  at a contact point  110 . The contact forces the disconnector back against a coil spring between the disconnector and the trigger, preventing the disconnector from moving forward as the trigger is further pulled, so it (the disconnector) may no longer latch the hammer. In this way the full auto rocker enables full automatic fire via standard auto sear  109  as long as the trigger position is maintained. 
     A relief slot is provided to the engaging surface of the safety selector (not illustrated here) to enable part clearance of the engaging portion of the selector while the selector is left in semiautomatic firing position. To return to semiautomatic firing the operator simply releases pressure against trigger  102 , allowing the trigger to return full auto rocker  106  to its original position in the assembly. Disconnector  104  may then move forward (clockwise rotation) to catch and latch hammer  103  until the trigger is again at the maximally forward position where the hammer rests against the forward end of the trigger prior to a next shot fired in semiautomatic mode. 
       FIGS. 3 ,  4  and  5  are different views of full auto rocker  106  of  FIG. 2  according to an embodiment of the present invention. Full auto rocker  106  includes an opening  203  placed inline through both rocker ends corresponding with the opening  107  in trigger  102  of  FIG. 1 . Opening  203  provides a passage for a pin (not illustrated) that passes through openings  203  and trigger opening  107 . The openings ( 203 ) may be drilled and then reamed to a tight tolerance and in true position relative to the cam-shaped ends of full auto rocker  106  so that the position of the auto rocker in the assembly is substantially parallel to the floor of the trigger system compartment. The pin (not illustrated) may be manufactured to an outside diameter (OD) just smaller than openings  203  to provide a snug slip fit. In this way, both ends make contact with the floor simultaneously and pressure is distributed equally over the auto rocker arm to the disconnector. 
     Full auto rocker  106  has a relief radius  205  provided at a strategic location in each auto rocker arm at a position where the elongate body portion of the rocker meets the cam-shaped end of the rocker. The relief radii are provided so that full auto rocker  106  does not contact any other components in the trigger system besides disconnector  104 . 
       FIG. 4  is a plan view of full auto rocker  106  of  FIG. 2 . Full auto rocker  106  in plan view exhibits a symmetrical profile. An auto rocker arm  301  and an auto rocker arm  303  are held substantially parallel and apart by a rear bridge element  305 . Openings  203  are inline with one another, full auto rocker  106  may be machined from a piece of stainless steel or other durable metal. The overall length of full auto rocker  106  is held such that wall  305  makes contact at contact point  110  with the back surface of disconnector  104 . 
       FIG. 5  is an end view of full auto rocker  106  of  FIG. 2 . Viewed from the left end of full auto rocker  106  of  FIG. 2 , arms  301  and  303  and back wall  305  are visible. Full auto rocker  106  is pinned at openings  203  to the trigger in the trigger system at an opening provided through the trigger to accommodate the pin. The gap distance between the inside of arm  301  and the inside of arm  303  is sufficiently wide to enable full auto rocker  106  to fit over the trigger accommodating the disconnector and the hammer within the gap. 
       FIG. 6  is an elevation view of a safety selector switch  500  modified to practice the invention. Safety selector switch  500  is a standard selector switch that is modified to practice the invention by provision of a relief slot  501  placed into the portion of the selector that contacts the disconnector and full auto sear unit  109  described further above in  FIG. 1 . The relief enables the selector to remain in semi automatic mode with the full auto sear ( 109 ) engaged and the disconnector ( 104 ) disengaged from the hammer. 
       FIG. 7  is a left-end view of safety selector  500  of  FIG. 5 . Viewed from the end, selector  500  is shown as it would be presented to an operator on the face of the trigger compartment unit housing the trigger system. Relief slot  501  is presented at a slight angle and is sufficiently deep to provide the required relief. 
     Safety selector  500  and trigger  102  are the only standard parts of trigger system ( 101 ) that have to be modified in order to accommodate full auto rocker  106  into the trigger system as a functioning component. 
       FIG. 8  is a process flow chart illustrating steps  700  for practicing full automatic fire from semi-automatic mode according to an embodiment of the present invention. An operator of the rifle sets the safety selector to semi-automatic mode at step  701 . This setting enables single shot semiautomatic firing by pulling and releasing the trigger. The operator pulls the trigger while in semiautomatic firing mode to fire a single shot in that mode at step  702 . The operator may make a decision at step  703  whether to advance to automatic firing while remaining in a semiautomatic firing mode. 
     If at step  703  the operator determines not to engage automatic firing then the process loops back to step  702  where the operator continues to fire in semiautomatic mode by pulling on the trigger to fire a shot then releasing the trigger to prepare for the next shot. If at step  703  the operator decides to engage in automatic firing while the safety selector is set to semiautomatic firing mode, then at step  704  the operator pulls the trigger back with added pressure and does not release the trigger. The operator may develop a feel for the variable amount of pressure required to engage automatic fire in semiautomatic firing mode. 
     The full auto rocker makes contact with the floor of the trigger system compartment at step  705  as the trigger is pulled further back. The rocker arm ends forced against the floor cause the full auto rocker to rotate counterclockwise about the pin connecting the rocker to the trigger. The forced rotation causes the full auto rocker to press down on the disconnector at step  706  releasing the disconnector from the hammer. 
     The operator maintains full automatic firing at step  707  while maintaining the pressure applied to the trigger. The auto sear unit operates normally and the slot relief provided in the safety selector prevents it from moving out of semiautomatic mode. At step  708  the operator may decide whether to return to semiautomatic firing or not. 
     If the operator decides not to return to semiautomatic firing, the process loops back to step  707  and full pressure is maintained on the trigger to continue automatic fire. If the operator chooses to return to semiautomatic firing then at step  709  the operator releases the trigger causing the disconnector to engage the hammer and the hammer to engage the forward end of the trigger enabling the disconnector to disengage from the hammer. Semiautomatic firing is resumed as the process loops back to step  702 . 
     With the full auto rocker ( 106 ) of the invention, the operator may in semiautomatic firing mode, switch from semiautomatic firing to automatic firing and back at will by varying the pressure applied to the trigger component. The operator is not required to switch the safety selector to automatic firing mode. 
     The full auto rocker of the present invention is illustrated in a trigger system that is typical of an M-16 military rifle. However, invention is not limited to an M-16 rifle. The auto rocker may be installed in a trigger system belonging to an AR-15 military rifle and other similar weapons without departing from the spirit and scope of the present invention. Adapting the auto rocker to other trigger systems may require somewhat different modifications of the integral components of the trigger system. For example, the location of the opening provided in the trigger may be different and there may be differences in slot relief for the safety selector without departing from the spirit and scope of the present invention. 
     It will be apparent to one with skill in the art that the full auto rocker system of the invention may be provided using some or all of the mentioned features and components without departing from the spirit and scope of the present invention. It will also be apparent to the skilled artisan that the embodiments described above are specific examples of a single broader invention which may have greater scope than any of the singular descriptions taught. There may be many alterations made in the descriptions without departing from the spirit and scope of the present invention.