Abstract:
A two-stage trigger assembly for the M16 or AR15 weapon systems. The trigger assembly comprises a spring loaded hammer, trigger and disconnector. Calibrated springs are provided to facilitate the adjustment of the second stage trigger pull weight. No set screws adjustments are necessary and a secondary safety sear similar to the factory original fire control components has been incorporated to prevent the unintentional mechanical discharge of the firearm. Installation of the disclosed device is identical to the factory fire control group and requires no hand fitting.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of Invention 
         [0002]    This application relates in general to two-stage trigger systems with improved safety and manufacturability features for semi-automatic weapons and specifically to the use of said trigger assembly on an AR-15 type rifle. 
         [0003]    2. Prior Art 
         [0004]    The trigger assembly of the proposed invention was designed to increase the control an individual shooter has over the timing of the host firearms discharge of a round and thereby effectively increase the accuracy potential of a shooter by minimizing mechanical distractions which hinder accurate gun fire. A smooth crisp trigger is essential if the user is to control when the firearm discharges. Precision shooters, be they military, law enforcement or civilian competitors require total control of the trigger mechanism to attain 
         [0005]    the maximum accuracy potential of their rifle. For military and law enforcement precision shooters control over the trigger mechanism is essential to the success of their respective missions. 
         [0006]    Under optimal conditions a shooter wants to use as little force as is necessary to discharge his firearm. By minimizing the force necessary to manipulate the trigger group and thereby discharge the firearm the potential for pulling the firearm off target while manipulating the trigger is dramatically reduced. Lightening the trigger is an obvious solution to solving trigger related accuracy problems but concerns over safety must also be considered. Reducing the trigger pull weight also presents the potential for accidental or negligent discharges which can result in the loss of life, which is of particular concern to law enforcement and military end users. 
         [0007]    Two stage triggers, which are well known in the prior art, allow for a smooth first stage and a light, crisp second stage which results in the firearm being discharged after the resistance is overcome. Two-stage triggers address many of the safety concerns which are present with light weight single stage triggers. Unfortunately many existing designs require the adjustment of set screws and/or the reduction of spring tension necessary to operate the hammer component of the trigger assembly. Set screws such as those found in U.S. Pat. No. 6,131,324 (Arnold W. Jewell) have a tendency to become threadedly unsecured after prolonged use. This often leads to a situation where the trigger either allows the uncontrolled discharge of the host weapon or prohibits the weapons from firing at all, this presents an obvious safety problem and concern for the user of a firearm equipped with such a trigger. A design which provides a smooth, crisp, and controlled trigger pull without the need of set screws if highly desirable. The design disclosed in this document requires no set screws to adjust the trigger pull weight and incorporates several safety features to prevent negligent discharge of the firearm. 
         [0008]    Designs such as Rock River Arms two stage trigger rely on similar trigger disconnector geometry as found on factory AR15 or M16 triggers. These designs have a flat surface to surface contact which in the case of a pivoting component contacting another stationary component a flat surface to surface contact is extremely difficult to achieve as any deviation from perfect component size will in fact cause the two surfaces to not sit flat to each other thereby negatively affecting the primary sear engagement thus affecting the trigger pull weight. Any inconsistency between these two flat surfaces will dramatically and negatively affect the trigger mechanism as a whole. By providing a non linear surface with a partial radius on the trigger a line contact between the flat face of the disconnector and the partial radius on the trigger is provided, not a flat surface to flat surface contact. An another embodiment of the design could place the radius onto the disconnector face with the trigger surface being flat, the end result would be the same. With a flat surface contacting a cylindrical surface any differences in component size or position from ‘perfect’ will still allow the intended line contact at a point near where intended. This is a key aspect to providing a production two stage trigger which has a consistent, reliable trigger pull between each article of manufacture without the need of adjustable set screws or hand fitting. 
         [0009]    While other designs such as those disclosed in U.S. Pat. No. 6,131,324 (Arnold W. Jewell) and U.S. Pat. No. 5,501,134 (Milazzo) require the adjustment of problematic set screws to adjust trigger pull weight the novel design described herein has incorporated another solution. Through the use of calibrated disconnector springs the trigger pull weight may be lowered or increased. This change in no way affects the reliability or safety of the trigger. While designs such a disclosed in U.S. Pat. No. 5,501,134 (Milazzo) do offer lighter disconnector springs, adjusting the set screws is still necessary to ensure proper function of such designs. 
         [0010]    A safety sear similar to the primary sear present on the factory M16 or AR15 trigger group is also present. Many available triggers on the market do not have a secondary safety sear which would prevent the firearm from discharging should the primary sear break. This is of particular concern if the firearm is loaded and the firing mechanism is in the operational or “cocked” position. My design has incorporated a safety sear which will catch the hammer and prevent the weapon from discharging even if the primary sear brakes. 
         [0011]    The present invention greatly reduces the probability of accidental firearm discharge while at the same time providing the user of a firearm appropriately equipped with desired trigger action characteristics. Shot to shot consistency of pull weight and travel is insured without abnormal manipulation or motion between shots. 
         [0012]    Another improvement over other two stage triggers is the use of a precision sheet metal fabrication for the disconnector. The original M16 disconnector is manufactured by fineblanking which is a sheet metal stamping operation that will produce a part to close tolerances and fine surface finish on the edges of the part. Current two stage triggers that locate the primary sear above the trigger pin use investment castings or machined from solid metal disconnectors. Investment castings and machined disconnectors usually cost more per piece than an equivalent fineblanked or laser cut disconnector that is made from sheet metal. A sheet metal disconnector that is carried in the conventional M16 manner can be made to properly interface with a select-fire M16 safety selector so that a two stage trigger capable of fully automatic fire may be easily designed. The current invention carries a sheet metal disconnector in a trough that is located in the trigger in a manner similar to the original M16 disconnector. However, where the original M16 disconnector is located in an open trough whereas the current invention covers over part of the trough with a structure that carries the two stage trigger primary sear. This structure has an aperture or void that allows the disconnector to pass through the structure so that the disconnector stop may be located forward of the trigger pin. 
         [0013]    3. Objects and Advantages 
         [0014]    Accordingly several objects and advantages of the present invention are
   (a) To provide a trigger mechanism which has no threadedly secured adjustment points.   (b) To provide a trigger mechanism that does not require modification of the receiver or trigger mechanism to function in an AR15 or M16 based weapon system.   (c) To provide a secondary safety sear that will prevent the hammer from falling if the trigger is not pulled and/or the primary sear fails.   (d) To provide a non linear stop for the disconnector which is machined onto the trigger to minimize the effect foreign particles might have on the trigger pull weight and to provide consistent sear engagement between each article of manufacture.   (e) To provide an improved trigger mechanism that requires no fitting or adjustment by the user.   (f) To provide a trigger mechanism that is easy and cost effective to manufacture by the use of a sheet metal disconnector.   
 
         [0021]    Still further objects and advantages will become apparent from a consideration of the ensuing description and drawings. 
       SUMMARY 
       [0022]    In general terms the present invention provides two stage trigger mechanism consisting of a spring loaded trigger, hammer, and disconnector. No adjustment or hand fitting is required for the installation of the presented invention, a feature that sets it apart from many other existing designs. 
         [0023]    Specifically my device affords several advantages over other existing designs. There are no set screws which may become threadedly unsecured rendering the trigger inoperable. A secondary safety sear has been included to prevent a negligent discharge should the primary sear fail for an unforeseen reason. A non linear stop has been provided for the disconnector to facilitate a consistent trigger pull weight even after prolonged use and the accumulation of debris associated with the use of a firearm. A simple, robust sheet metal disconnector is also provided that is easy and cost effective to manufacture. 
         [0024]    A method of installation has been afforded the users of this device which requires no modification of the receiver or of the trigger assembly such as required by the design disclosed in U.S. Pat. No. 5,501,134 (Milazzo). Further the proposed novel trigger mechanism installs exactly like the factory original trigger mechanism. 
         [0025]    While the proposed apparatus is designed for the AR15/M16 weapons system this should not be seen as a limitation of the overall application and potential use of the technology disclosed in the application. 
     
    
     
       DRAWINGS 
         [0026]    The novel features believed to be characteristic of the invention, together with further advantages thereof, will be better understood from the following description considered in connection with the accompanying drawings in which a preferred embodiment of the present invention is illustrated by way of example. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention. 
           [0027]      FIG. 1  shows a side view of the trigger mechanism, where the hammer is in the cocked position; 
           [0028]      FIG. 2  shows an exploded, three dimensional view of the present invention and how it is assembled; 
           [0029]      FIG. 3  shows a top view of the proposed trigger; 
           [0030]      FIG. 4  shows an internal, side view of the proposed trigger mechanism; 
           [0031]      FIG. 5  shows details of the non-linear disconnector stop and the disconnector present on the proposed trigger assembly; 
           [0032]      FIG. 6  shows details of the safety sear on the forward end of the trigger and how it interacts with the hammer catch; 
           [0033]      FIG. 7  shows details of how the triggers individual parts interact when in the cocked position; 
           [0034]      FIG. 8  shows a flow chart detailing the means by which the user may replace the weight calibrated disconnector springs; 
           [0035]      FIG. 9  shows an exploded, three dimensional view of an alternate embodiment of the invention and how it is assembled; 
           [0036]      FIG. 10  shows an exploded, three dimensional view of an alternate embodiment of the invention and how it is assembled; 
           [0037]      FIG. 11  shows an exploded, three dimensional view of an alternate embodiment of the invention and how it is assembled; 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0038]    Turning now to the drawings in which like reference characters indicate corresponding elements throughout the several views, as used herein, the word “front” or “forward” corresponds to the end of the trigger assembly where the safety sear is located (i.e., to the right as shown in  FIGS. 1 ,  2 ,  3 ,  4 ); “rear” or “rearward” or “back” corresponds to the direction opposite the end of the trigger assembly where the safety sear is located (i.e., to the left as shown in  FIGS. 1 ,  2 ,  3 ,  4 ). 
         [0039]    Attention is first directed to  FIG. 1  which illustrates the trigger mechanism, generally designated  20  and  FIG. 2  which is an exploded view of the trigger mechanism  20  of  FIG. 1 . It will be understood that trigger mechanism  20  is intended to be employed with any of the various M16 type firearms; however with minor modifications it could be more widely used for other firearms as well. M16 type firearms include the AR15 family of rifles, the M4 carbine family of rifles, the SR25 and AR10 larger caliber type M16 rifles and other rifles that use the AR15 trigger assembly. It will also be understood that trigger mechanism  20  is carried by a lower receiver of a firearm. A lower receiver is not shown, as they are well known in the art and trigger mechanism  20  is carried in the conventional manner using trigger pin  30  and hammer pin  32 . Trigger mechanism  20  has a spring loaded trigger assembly  22  having a trigger sear hook  21  and a spring loaded hammer  24  having a hammer sear hook  23 . The trigger assembly spring and hammer spring are omitted for clarity. Trigger assembly  25  includes a trigger  22 , spring loaded disconnector assembly  26 . The trigger assembly  25  is pivotally connected to trigger pin  30  that passes from one side of trigger  22  through disconnector assembly  27  and through opposite side of trigger  22 . In the cocked position shown in  FIG. 1  the trigger sear hook  21  is fully engaged in hammer sear hook  23 . 
         [0040]    Referring to  FIG. 2 , disconnector assembly  27  includes a disconnector  26 , disconnector spring  28 . Trigger  22  has a nose  36  at one end and a trough  40  formed therein extending from the opposing end. Trough  40  includes a placement for disconnector spring  28 . The trigger sear hook  21  is part of trigger assembly  25 . There is an aperture  42  through the structure which incorporates the trigger sear hook  21 . This aperture  42  allows the disconnector  26  to pass through and under the trigger sear hook  21  placing the disconnector  26  stop point forward of the trigger sear hook  21 . 
         [0041]    Turning to  FIG. 3  which is a plan view of the trigger mechanism of  FIG. 1 , the trough  40  is clearly shown into which the disconnector assembly  27  resides. 
         [0042]    Referring to  FIG. 4  which is a sectional view of  FIG. 3  on the line A-A the disconnector  26  pivots on a trigger pin  30  and bears on the surface of the trigger pivot pin  30 . Hammer sear hook  23  and trigger sear hook  22  form the trigger and hammer engagement means. In the cocked position shown in  FIG. 4  the hammer sear hook  24  is fully engaged in trigger sear hook  22 . Pulling the trigger  29  causes the trigger  22  and disconnector assembly  27  to rotate about trigger pin  30  and pull the trigger sear hook  21  off the hammer sear hook  23 . Disconnector spring  28  is removable from the trough  40  when trigger pin  30  is removed from trigger  22 , this removable spring is the means for adjusting the amount of resistance which is required to overcome the disconnector  26  resistance. By allowing the user to vary the resistance of spring  28  the force imparted to disconnector  26  may be varied. 
         [0043]    Additionally,  FIG. 5  is an enlarged view of the non linear trigger stop  50 . On the trigger  22  the non linear surface is a partial radius  51  while the disconnector contact surface  52  is flat. The partial radius  51  located on the trigger  22  is machined in such a way as to facilitate a line contact between the trigger  22  and the disconnector contact surface  52 . 
         [0044]    Additionally,  FIG. 6  is an enlarged view of the secondary safety sear  60 , the nose  36  of the trigger  22  and the notch  37  of the hammer  24  form the means by which the secondary safety sear functions. In the event that trigger sear hook  21  or hammer sear hook  23  fail, the secondary safety sear which is a function of both notch  37  and nose  36  will prevent the hammer  24  from being activated by its associated spring. Spring for the hammer  24  was left out of illustration for reasons of clarity. The notch  37  and nose  36  each have opposing surfaces which will passively come into contact with each other without the trigger  29  being pulled rearward. 
         [0045]    Turning to  FIG. 7 , which is a side view of the trigger mechanism  20  where the trigger mechanism  20  is in a cocked position similar to  FIG. 4  but with the trigger  29  pulled thereby rotating the trigger assembly  25  clockwise around trigger pivot pin  30  while overcoming resistance of a trigger spring that is not shown for clarity. In  FIG. 6  the trigger  22  has been pulled until the hammer sear hook  23  has contacted disconnector face  41  of disconnector  26  and overlap of the hammer sear hook  23  and trigger sear hook  21  has been reduced. At this point in the process of pulling the trigger  29  the shooter will feel a distinct stop point where the secondary hammer sear hook  23  is attempting to rotate disconnector  26  around trigger pivot pin  25  in a counter-clockwise direction. The location of this stop point controls the amount of overlap left on the hammer sear hook  23  and trigger sear hook  21  and marks the end of the 1 st  stage of trigger pull. A minimal amount of overlap is desired as only a slight amount of additional pressure on the trigger  29  will rotate the disconnector  26  counter-clockwise and allow the trigger sear hook  21  to slip off the hammer sear hook  23  thereby allowing the hammer  24  to rotate under the force of the hammer spring and strike the firing pin, discharging the firearm. This slight additional pressure on trigger  29  is known as the 2 nd  stage and allows the shooter to carefully align his sights on target and at the appropriate moment the slight additional pressure on trigger  29  will allow the firearm to discharge without disturbing the alignment of the firearm sights. The removal and subsequent replacement of the disconnector spring  28  allows the user to adjust the amount of force necessary to rotate the disconnector  26  counter-clockwise thereby affecting the amount of resistance necessary to complete the 2 nd  stage of the trigger pull  29 . 
         [0046]    Referring to  FIG. 8 , there is shown a flow diagram of a method  70  of replacement for the disconnector spring  28 , thereby affecting the 2 nd  stage trigger pull weight. Remove the trigger assembly  20  from the weapon  71 . Remove  72  the disconnector  26  from the trigger  22 . Remove  73  the disconnector spring  28  then select from a plurality of provided pre-calibrated springs  74  which will adjust the amount of force necessary to modify the weight of the 2 nd  stage trigger pull which results in the discharge of the host firearm. Install  75  the selected disconnector spring  28 . Reinstall  76  the disconnector  26  and trigger  77  assemblies  20  in weapon. Now the user needs to test  78  the trigger  29  pull weight and see if the pull weight is as desired, if not then repeat the steps described on the disconnector spring replacement chart  70 . If the trigger pull weight is as desired no further action need be taken  80 . 
         [0047]    Referring to  FIG. 9 , there is shown an alternate embodiment of the present trigger assembly  20 . The significant deviation from the preferred embodiment as illustrated and described in  FIGS. 1  thru  8  are as follows. The secondary safety sear  60 , nose  36  of the trigger  22 , and the notch  37  of hammer  24 , non linear stop  50 , and partial radius  51  have been removed. 
         [0048]    Referring to  FIG. 10 , there is shown an alternate embodiment of the present trigger assembly  20 . The significant deviation from the preferred embodiment as illustrated and described in  FIGS. 1  thru  8  are as follows. The non linear stop  50 , and partial radius  51  have been removed. 
         [0049]    Referring to  FIG. 11 , there is shown an alternate embodiment of the present trigger assembly  20 . The significant deviation from the preferred embodiment as illustrated and described in  FIGS. 1  thru  8  are as follows. The secondary safety sear  60 , nose  36  of the trigger  22 , and the notch  37  of hammer  24  have been removed. 
       CONCLUSION, RAMIFICATIONS, AND SCOPE 
       [0050]    Accordingly the reader will see that, according to the invention, I have provided a two stage trigger system with improved safety features, reliable pull weights, and a device which is durable. I have afforded the user of my device a means to adjust the 2 nd  stage of my triggers pull weight without the need of problematic, adjustable screws. I have even provided a secondary safety sear to afford a military or law enforcement operator added safety when working in close confines with team mates. 
         [0051]    While my above drawings and description contain many specificities, these should not be construed as limitations on the scope of the invention, but rather as an exemplification of one preferred embodiment thereof. The omission of the calibrated disconnector springs will not depart from the essential nature of the proposed invention. Further an embodiment of the invention may be had which omits the secondary safety sear and/or the partial radius located on either the trigger or disconnector contact surfaces. Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their legal equivalents.