Patent Publication Number: US-2023136519-A1

Title: Trigger mechanism for a firearm

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. patent application Ser. No. 17/515,009, filed on 29 Oct. 2021, now pending. 
    
    
     FIELD 
     The described examples relate generally to firearms. More particularly, the present examples relate to trigger mechanisms for firearms. 
     BACKGROUND 
     Whether hunting wild game, competing in competitive shooting events, or participating in recreational shooting with family and friends, firearms and the shooting sports incorporating firearms have been popular and prevalent in society for generations. There are many forms of firearms including handguns, rifles, shotguns, and so on. A firearm generally includes a barrel, a stock or grip, a trigger mechanism, and a firing mechanism (i.e., the action). The firearm can utilize a bolt action, a lever action, a pump action, an automatic action (e.g., semi-automatic or fully automatic), or another type of action. Each component of the firearm can impact or otherwise affect the overall accuracy, durability, safety, performance, and functionality of the firearm. Thus, improvements and innovations to the components of a firearm can be desirable to increase the efficacy of the firearm when utilized within shooting sports and other endeavors. 
     SUMMARY 
     According to some aspects of the present disclosure, a trigger mechanism can include a housing, a first sear, a second sear, a third sear, and a trigger. The second sear can be coupled to the first sear. The second sear can rotate relative to the housing. The third sear can be rotatably coupled to the housing. The third sear can form a surface that engages with a distal end of the second sear to prevent rotation of the second sear. The trigger can disengage the surface of the third sear from the distal end of the second sear when the trigger is rotated. 
     In some examples, the trigger mechanism can further include a sear linkage coupling the first sear to the second sear. The sear linkage can be rotatably coupled to the first sear by a first pin. The second sear can be rotatable relative to the housing about an axis. The sear linkage can be rotatably coupled to the second sear by a second pin. The second pin can be laterally offset from the axis. When the trigger is rotated, the surface of the third sear can transition relative to the distal end of the second sear a distance before disengaging from the distal end of the second sear. The surface of the third sear can transition relative to the distal end of the second sear before disengaging from the distal end of the second sear. For example, the first sear can include a distal end and a proximal end. The sear linkage can be coupled to the distal end of the first sear. The first sear can be rotatably coupled to the housing at the proximal end of the first sear. The first sear can be configured to retain a striker in a biased state while the surface of the third sear is engaged with the distal end of the second sear. The third sear can be biased to retain engagement between the surface of the third sear and the distal end of the second sear. A spring can contact the second sear and bias the second sear to rotate about a pin rotatably coupling the second sear to the housing. 
     According to another aspect of the present disclosure, a firearm can include a stock, a barrel, a receiver, a bolt assembly, and a trigger mechanism. The receiver can be configured to couple to the stock and the barrel. The bolt assembly can include a firing pin. The trigger mechanism can be disposed at least partially within the receiver. The trigger mechanism can include a housing, a first sear or striker sear, a second sear or main sear, a third sear or trigger sear, and a trigger. The second sear can be coupled to the first sear and rotatably coupled to the housing. The third sear can be rotatably coupled to the housing. The third sear can engage with the second sear to prevent rotation of the second sear. The third sear can disengage from the second sear to permit rotation of the second sear when the trigger is rotated. 
     In some examples, the firing pin can be biased to move toward the barrel. The first sear can prevent the firing pin from moving toward the barrel. The firing pin can exert a force on the first sear. The trigger mechanism can also include a sear linkage coupled to the first sear and the second sear. The force exerted on the first sear can at least partially transfer to the second sear through the sear linkage. At least a portion of the force exerted on the striker sear can be at least partially applied on the main sear through the sear linkage. The main sear can engage the trigger sear at a first end of the main sear. The sear linkage can be coupled to the main sear at a second end of the main sear. The trigger sear can be biased to engage the main sear. The trigger mechanism can also include a locking member that limits the firing pin from moving toward the barrel while the locking member is in a first position, and can enable the firing pin to move toward the barrel while the locking member is in a second position. 
     According to another aspect of the present disclosure, a trigger mechanism can include a housing, a sear, an actuator, a trigger, a first biasing member, and a second biasing member. The sear can be rotatably coupled to the housing. The actuator can be rotatably coupled to the housing. The actuator can engage with the sear to prevent rotation of the sear. The trigger can disengage the actuator from the sear when the trigger is rotated. Each of the first and second biasing members can bias the actuator to engage the sear. 
     In some examples, the first and second biasing members can be adjustable to vary a force required to rotate the trigger and disengage the actuator from the sear. The force can be greater than 1 pound in some examples. An amount of biasing force exerted on the actuator from the first biasing member can be adjustable by rotating a first fastener at least partially disposed within the housing. An amount of biasing force exerted on the actuator from the second biasing member can be adjustable by rotating a second fastener at least partially disposed within the housing. A biasing force generated by the first biasing member can be different from a biasing force generated by the second biasing member. 
     Features from any of the disclosed examples can be used in combination with one another, without limitation. In addition, other features and advantages of the present disclosure will become apparent to those of ordinary skill in the art through consideration of the following detailed description and the accompanying drawings. At least one of the biasing members can be a coiled spring. The housing can form a first aperture and the first biasing member can be at least partially disposed within the first aperture. The housing can form a second aperture and the second biasing member can be at least partially disposed within the second aperture. At least one of the first biasing member or the second biasing member can be retained within the housing between a fastener and the actuator. The fastener can include an engagement structure forming a tamper proof interface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings illustrate several examples of the present disclosure, wherein identical reference numerals refer to identical or similar elements or features in different views or examples shown in the drawings. 
         FIG.  1 A  is a side perspective view of a firearm. 
         FIG.  1 B  is a side perspective view of the firearm of  FIG.  1 A  having a bolt in a retracted position. 
         FIG.  2    is a cross-sectional side view of a traditional trigger mechanism. 
         FIG.  3 A  is a side cross-sectional view of a trigger mechanism. 
         FIG.  3 B  is a detailed view of the trigger mechanism of  FIG.  3 A . 
         FIG.  4 A  is a cross-sectional side view of a trigger mechanism in a first configuration. 
         FIG.  4 B  is a cross-sectional side view of a trigger mechanism in a second configuration. 
         FIG.  5 A  is a cross-sectional side view of a biasing mechanism for a trigger mechanism. 
         FIG.  5 B  is a partially exploded cross-sectional side view of the biasing mechanism for the trigger mechanism of  FIG.  5 A . 
         FIG.  5 C  is a bottom perspective view of the biasing mechanism of  FIG.  5 A . 
         FIG.  5 D  is a cross-sectional side view of another example of a biasing mechanism for a trigger mechanism. 
         FIG.  6 A  is a bottom perspective view of a biasing mechanism for a trigger mechanism. 
         FIG.  6 B  is a bottom perspective view of a biasing mechanism for a trigger mechanism. 
         FIG.  6 C  is a bottom perspective view of a trigger mechanism. 
         FIG.  6 D  is a bottom perspective view of a trigger mechanism. 
         FIG.  6 E  is a bottom perspective view of a trigger mechanism. 
         FIG.  6 F  is a bottom perspective view of a trigger mechanism. 
     
    
    
     DETAILED DESCRIPTION 
     The present description provides examples, and is not limiting of the scope, applicability, or configuration set forth in the claims. Thus, it will be understood that changes can be made in the function and arrangement of elements discussed, without departing from the spirit and scope of the disclosure, and various examples can omit, substitute, or add other procedures or components, as appropriate. Also, features described with respect to some examples can be combined in other examples. 
     A firearm can include a number of components and mechanisms which function in tandem to enable operation of the firearm. For example, a firearm can generally include one or more barrels, a stock or grip, a trigger mechanism, and a firing mechanism (i.e., the action). Efficient operation of each of these components can contribute to the overall performance of the firearm. The trigger mechanism can act as an interface between the shooter and the firearm. As such, characteristics of the trigger mechanism, such as trigger pull weight and the trigger pull travel, can directly correlate with the feel and performance of the firearm. A component of the trigger mechanism, such as a striker sear, can retain a firing pin or a striker of the firearm in a rearward position. Because the striker is biased to transition toward the firing chamber of the barrel, the striker can exert a force on the striker sear while the striker is in the rearward position. In some trigger mechanisms, this force can increase friction between components of the trigger mechanism, and thereby increase the pull weight of the trigger (i.e., increase the force required to pull the trigger to release the striker and discharge the firearm). Many shooters, however, desire a firearm having a reduced and/or adjustable trigger pull weight to customize the characteristics of their firearm and to optimize their performance. 
     The present disclosure relates to trigger mechanisms for firearms. In one aspect of the present disclosure, trigger mechanisms are described which utilize a linkage between a striker sear and a main sear to control an amount of force applied to the main sear by the striker sear. For example, a portion of the force exerted on the striker sear by the striker can be exerted on the main sear through a sear linkage. As described herein, the force applied on the striker sear by the striker and a ratio of moment arms defined by components within the trigger mechanism can correlate to a lesser force exerted on the trigger sear by a main sear. In other words, a force applied between the main sear and the trigger sear can amount to only a portion of the force exerted on the striker sear by the striker. Thus, frictional forces between the main sear and trigger sear of the trigger mechanism can be reduced to enable a relatively lesser trigger pull weight. 
     In another aspect of the present disclosure, trigger mechanisms are described which additionally, or alternatively, utilize one or more biasing members to provide a variable trigger pull weight. For example, one or more biasing members can engage an actuator or a trigger sear to apply resistance against rotation of the trigger sear when a trigger is pulled. The one or more biasing members can be compressed and/or decompressed to vary (e.g., increase or decrease) the amount of force required to rotate the trigger sear. A first biasing member can be set such that a minimum trigger pull weight is set and a second biasing member can be adjustable to increase or decrease the trigger pull weight to a value equal to or above the minimum trigger pull weight. This aspect will be described in greater detail below with reference to  FIGS.  5 A- 6 F . 
     These and other examples are discussed below with reference to  FIGS.  1 A- 6 F . However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these Figures is for explanatory purposes only and should not be construed as limiting. While the present disclosure primarily references trigger mechanisms or systems which are disposed within a firearm, persons having skill in the art will readily appreciate that any of the aspects described herein can be applied to an aftermarket trigger mechanism that is designed for a specific firearm but sold separately from the firearm. Similarly, the present trigger mechanisms and configurations can be integral to a complete firearm, or can be included in a stand-alone drop-in trigger mechanism used in any number of firearm types and platforms. 
       FIG.  1 A  shows an example of a firearm  100  including a barrel  102  coupled to a receiver  104 . The firearm  100  can also include a bolt  106  disposed within the receiver  104  and repositionable relative to the receiver  104 . The firearm can include a trigger guard  108  and a trigger  110  at least partially positioned within the trigger guard  108 . The trigger  110  can be a component of a trigger mechanism (see  FIG.  3 A ) coupled to the receiver  104  and/or the bolt  106  of the firearm  100 . One or more of the barrel  102 , the receiver  104 , the bolt  106 , and the trigger  110  can be at least partially disposed within a stock  112  of the firearm  100 . 
       FIG.  1 B  shows the firearm  100  with the bolt  106  in a retracted or rearward position (i.e., slid rearward from the barrel  102 ). The bolt  106  can be retracted or slid rearward from the barrel  102  by rotating the bolt  106  using a bolt knob  114  affixed to the bolt  106 . For example, the bolt knob  114  can be lifted from an initial position (shown in  FIG.  1 A ) to rotate the bolt  106  and subsequently slid rearward from the barrel  102  to expose an ejection port  116  within the receiver  104 . While the bolt  106  is in a retracted or rearward position, an ammunition cartridge  118  can be inserted into or ejected from the receiver  104 . For example, the ammunition cartridge  118  can be a spent or discharged ammunition cartridge which is ejected from the receiver  104  when the bolt  106  is slid backward to the rearward position. While  FIGS.  1 A and  1 B  illustrate a bolt-action rifle, the present systems and methods can be incorporated into any type of firearm having any number of actuation types including, but in no way limited to, bolt-actions, break-actions, lever-actions, pump-actions, and/or semi-automatic action types. 
       FIG.  2    shows a prior art trigger mechanism  200  and a striker  202 . The trigger mechanism  200  can include a striker sear  204 , a trigger sear  206 , and a trigger  208  disposed within a housing  210 . The striker sear  204 , the trigger sear  206 , and the trigger  208  can be rotatably coupled to the housing  210  by respective pins  212 ,  214 ,  216 . When the trigger  208  is pulled (i.e., rotated about pin  216 ), a surface  218  of the trigger  208  can engage the trigger sear  206  to cause the trigger sear  206  to rotate about pin  214 . When the trigger sear  206  rotates about the pin  214 , a surface  220  of the trigger sear  206  can be pulled away from an engagement portion  222  of the striker sear  204  to allow the striker sear  204  to rotate about the pin  212  and subsequently release the striker  202  and discharge the firearm (i.e., cause the striker assembly to contact an ammunition cartridge disposed within a firing chamber of the barrel). 
     The striker sear  204  can engage the striker  202  to temporarily retain the striker  202  in a rearward position (i.e., displaced a distance from the barrel). The striker  202  can be biased to transition toward the barrel (not shown) as illustrated by a directional arrow  224 . While the striker  202  is temporarily retained in the rearward position by the striker sear  204 , the striker  202  can exert a force on the striker sear  204  which biases the striker sear  204  to rotate about pin  212 . This force, (shown as arrow  226 ), can generate relatively large frictional forces between the surface  220  of the trigger sear  206  and the engagement portion  222  of the striker sear  204 . The relatively large frictional forces can increase the associated pull weight of the trigger mechanism  200  (i.e., the force required to rotate the trigger about the pin  216  to discharge the firearm). In some examples, the trigger mechanism  200  can include a spring  228  which applies an opposing force (shown as arrow  230 ) on the striker sear  204  to counter some of the force exerted on the striker sear  204  by the striker  202 . 
     In one aspect of the present disclosure, examples of trigger mechanisms are described which utilize a sear linkage to at least partially reduce the frictional forces induced on components of the trigger mechanism and thereby reduce a trigger pull weight associated with the trigger mechanism. The sear linkage can enable a portion of the force exerted on a striker sear by a striker to be carried by a housing of the trigger mechanism instead of being carried entirely by a main sear. Examples of trigger mechanisms having a sear linkage are described below with reference to  FIGS.  3 A and  3 B . 
       FIG.  3 A  shows a cross-sectional view of a trigger mechanism  300  and a firing pin or striker  302 . The trigger mechanism  300  includes a striker sear  304  which engages the striker  302  to retain the striker  302  in a biased state (e.g., the striker  302  can be biased away from a barrel of a firearm such that the striker  302  can launch toward a firing chamber of the barrel when the striker sear  304  is disengaged from the striker  302 ). The striker sear  304  and a main sear  306  can be coupled by a sear linkage  308 . The main sear  306  and a trigger  310  can engage with respective portions of a trigger sear  312 . The striker sear  304 , the main sear  306 , the trigger sear  312 , and the trigger  310  can each be rotatably coupled to a receiver or housing  314  by respective pins  316 ,  318 ,  320 ,  322 . For example, the striker sear  304  can be rotatably coupled to the housing  314  by the pin  316  such that a distal end  324  of the striker sear  304  can move into and out of contact with the striker  302 . 
     The main sear  306  can be rotatably coupled to the housing  314  by the pin  318 , for example, the pin  318  can define an axis of rotation and the main sear  306  can rotate about the axis of rotation defined by the pin  318 . A distal end  326  of the main sear  306  can engage with the trigger sear  312  to prevent the distal end  324  of the striker sear  304  from rotating away from the striker  302 . The distal end  326  of the main sear  306  can be biased to engage with a planar surface  328  defined by the trigger sear  312 . For example, a force generated by a biasing element (e.g., a spring) of the striker  302  can be exerted on the striker sear  304 . The striker sear  304  can exert the force on the main sear  306  through the sear linkage  308 . The force exerted on the main sear  306  by the striker  302  can bias the distal end  326  of the main sear  306  to engage with the trigger sear  312 . However, as previously described, the force passed to the main sear  306  can generate relatively large frictional forces between the distal end  326  of the main sear  306  and the planar surface  328  of the trigger sear  312 , and can thereby generate a relatively heavy trigger pull weight. 
     The trigger  310  can be rotatably coupled to the housing  314  by the pin  322  such that rotation of the trigger  310  causes rotation of the trigger sear  312  about the pin  320 . For example, a user of the trigger mechanism  300  can rotate the trigger about the pin  322  using an index finger (i.e., the user can pull the trigger  310 ). Rotation of the trigger sear  312  about the pin  320  can cause the planar surface  328  of the trigger sear  312  to slide away from, or out of engagement with, the distal end  326  of the main sear  306 . When the planar surface  328  is rotated out of engagement with the distal end  326  of the main sear  306 , the main sear  306  can rotate about the pin  318  and enable the distal end  324  of the striker sear  304  to drop or otherwise disengage from the striker  302 . While the striker sear  304  is no longer engaging the striker  302 , the striker  302  can launch forward to contact an ammunition cartridge in the firing chamber of the firearm. 
     In some examples, the trigger mechanism  300  can also include a locking member  330  rotatably coupled to the housing  314  by a pin  332 . The locking member  330  can be attached to a switch  334  by a rod  336 . The switch  334  can be articulated by a user to transition the locking member  330  between a first position and a second position. While the locking member  330  is disposed in the first position (shown in  FIG.  3 A ), the striker  302  can launch forward to contact the ammunition cartridge in the firing chamber of the firearm. When the locking member  330  is actuated or rotated via the switch  334  to the second position, the locking member  330  limits or prevents the trigger sear from rotating and the striker  302  from launching forward to contact the ammunition cartridge and prevents discharge of the firearm. In some examples, the locking member  330  can include a first catch block  338  which interfaces with the trigger sear  312  to prevent excessive rotation of the trigger sear  312  (i.e., rotation beyond the rotation necessary to disengage the trigger sear  312  from the main sear  306 ) while the locking member  330  is in the second position. Additionally, or alternatively, the locking member  330  can include a second catch block  340  disposed adjacent to the striker  302  when in the second position and limits or prevents the striker  302  from launching forward to contact the ammunition cartridge in the firing chamber of the firearm. By impeding or substantially impeding horizontal or forward travel of the striker  302 , the second catch block  340  can immobilize the striker  302  to prevent unintentional discharge of the firearm. 
     In some examples, the trigger mechanism  300  can include a spring  342  which applies an opposing force on the striker sear  304  to at least partially counter a force exerted on the striker sear  304  by the striker  302 . The functionality of the various components of the trigger mechanism  300  will be discussed in greater detail below with regard to  FIG.  3 B . 
       FIG.  3 B  shows a detailed view of the trigger mechanism  300  shown in  FIG.  3 A . The striker  302  can exert a force F 0  on the striker sear  304  (e.g., a force applied by a spring affixed to the striker  302  which biases the striker  302  toward the barrel). The sear linkage  308  can be pivotably coupled to the main sear  306  by a pin  344 . The sear linkage  308  can be pivotably coupled to the striker sear  304  by a pin  346 . The force F 0  exerted on the striker sear  304  and a moment arm or distance D 0  between a line of action defined by the force F 0  and the pin  316  can define a first moment. At least a portion of the force F 0  exerted on the striker sear  304  can be applied to the sear linkage  308  because the striker sear  304  is coupled to the sear linkage  308 , for example, via the pin  346 . In order for the sear linkage  308  to remain in a fixed or static position relative to the striker sear  304  and the main sear  306  while the force F 0  is applied to the sear linkage  308 , a reaction force F 1  can be exerted on the striker sear  304 . The force F 1  can be equal to and opposing the portion of the force F 0  applied by the striker sear  304  onto the sear linkage  308 . The force F 1  exerted on the sear linkage  308  by the striker sear  304  and a moment arm or distance D 1  between a line of action defined by the force F 1  and the pin  316  can define a second moment. 
     The portion of the force F 0  exerted on the striker sear  304  can be transferred through the sear linkage  308  and applied to the main sear  306 , shown as force F 2 . The force F 1  and the force F 2  can be equivalent or substantially equivalent. The force F 2  can be exerted on the main sear  306  because the sear linkage  308  is coupled to the main sear  306 , for example, via the pin  344 . The force F 2  exerted on the main sear  306  and a moment arm or distance D 2  between a line of action defined by the force F 2  and the pin  318  can define a third moment. In order for the main sear  306  to remain in a fixed or static position relative to the sear linkage  308  and the trigger sear  312  while the force F 2  is applied to the main sear  306 , a force F 3  can be exerted on the distal end  326  of the main sear  306 . The force F 3  exerted on the distal end  326  of the main sear  306  and a moment arm or distance D 3  between a line of action defined by the force F 3  and the pin  318  can define a fourth moment. A magnitude of the force F 3  can correlate to the force F 0  exerted on the striker sear  304  and the respective distances D 0 , D 1 , D 2 , and D 3 . For example, the distance D 3  can be greater than the distance D 2  such that the force F 3  applied to the distal end  326  of the main sear  306  is less than the force F 2  exerted on the main sear  306  by the striker sear  304  through the sear linkage  308 . This lesser force F 3  (e.g., lesser than the force F 2 ) can correlate to a lighter trigger pull weight due to the lesser force F 3  applying relatively lesser frictional forces between the distal end  326  of the main sear  306  and the planar surface  328  of the trigger sear  312 . 
     In some examples, a reference plane P 0  can be drawn in line with the force F 0  (e.g., the line of action of F 0 ). The reference plane P 0  can extend generally parallel to the main sear  306  while the distal end  326  of the main sear  306  is engaging with the planar surface  328  of the trigger sear  312 . The pin  316  can be positioned at an offset or distance relative to the plane P 0 . For example, the pin  316  can be offset the distance D 0  from the plane P 0 . The distance D 0  can be at least about 1 millimeters (mm), between about 1 mm and about 3 mm, between about 3 mm and about 6 mm, between about 6 mm and about 15 mm, or less than about 20 mm. 
     In some examples, a reference plane P 1  can be drawn in line with the forces F 1 , F 2  (e.g., the line of action) and through the respective pins  344 ,  346  coupling the sear linkage  308  to the main sear  306  and the striker sear  304 , as shown in  FIG.  3 B . The reference plane P 1  can extend generally perpendicular to the distal end of the main sear  306  while the distal end  326  of the main sear  306  is engaging with the planar surface  328  of the trigger sear  312 . The pin  316  can be positioned at an offset or distanced relative to the plane P 1 . For example, the pin  316  can be offset the distance D 1  from the plane P 1 . The distance D 1  can be at least about 5 millimeters (mm), between about 5 mm and about 10 mm, between about 10 mm and about 15 mm, between about 15 mm and about 30 mm, or less than about 30 mm. The pin  344  can be laterally offset or distanced from the pin  316  which defines the axis of rotation of the main sear  306 . The pin  318  can be positioned at an offset or distanced relative to the plane P 1 . For example, the pin  318  can be offset the distance D 2  from the plane P 1 . The distance D 2  can be at least about 0.5 millimeters (mm), between about 0.5 mm and about 1 mm, between about 1 mm and about 3 mm, between about 3 mm and about 6 mm, or less than about 6 mm. 
     In some examples, a reference plane P 2  can be drawn through the pin  318  coupling the main sear  306  to the housing  314 . The reference plane P 2  can extend perpendicular to the planar surface  328  of the trigger sear  312 . The distal end  326  of the main sear  306  can engage the planar surface  328  of the trigger sear  312  on a first side of the reference plane P 2 . The pin  344  can be coupled to the main sear  306  on a second side of the reference plane P 2 . In some examples, the distal end  326  of the main sear  306  can engage the planar surface  328  of the trigger sear  312  at the distance D 3  from the plane P 2 . The distance D 3  can be at least about 5 millimeters (mm), between about 5 mm and about 10 mm, between about 10 mm and about 15 mm, between about 15 mm and about 20 mm, or less than about 20 mm. 
     As shown in Equations 1˜4 below, the respective forces F 0 , F 1 , F 2  and their moment arms or distances D 0 , D 1 , D 2 , along with the moment arm or distance D 3 , can correlate to the force F 3  exerted on the distal end  326  of the main sear  306 . For example, the distance D 2  and the distance D 3  can form a ratio, such as, a ratio of 0.176 wherein the distance D 2  is 1.5 mm and the distance D 3  is 8.5 mm (e.g., 1.5 mm/8.5 mm=0.176). The ratio can be at least about 0.05, between about 0.05 and about 0.1, between about 0.1 and about 0.5, between about 0.5 and about 0.7, or less than about 1. In other words, the force F 0  and the distances D 0 , D 1 , D 2 , D 3  can be selected (i.e., the trigger mechanism  300  can be designed and manufactured) such that the force F 3  does not generate undesirable frictional forces between the planar surface  328  of the trigger sear  312  and the distal end  326  of the main sear  306 . 
     
       
         
           
             
               
                 
                   
                     
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     In some examples, the force F 0  and the distances D 0 , D 1 , D 2 , D 3  can be selected such that the force F 3  does not exceed a desired maximum threshold or fall below a desired minimum threshold. For example, the force F 3  can be at least about 1 lb, between about 1 lb and about 2 lbs, between about 2 lbs and about 3 lbs, between about 3 lbs and about 5 lbs, or less than about 5 lbs. 
     In some examples, the trigger mechanism  300  may not include a sear linkage  308 . Instead, the striker sear  304  can be directly coupled to the main sear  306 . For example, a portion of the striker sear  304  can form a slot and the main sear  306  can be pinned or coupled to the slot such that the main sear  306  can rotate and translate (e.g., at least two degrees of freedom) relative to the striker sear  304 . While the reference plane P 1  is depicted as partially vertical in  FIG.  3 B , the trigger mechanism  300  can be rotated or modified, such that the reference plane P 1  can be more or less horizontal. 
       FIG.  4 A  shows a cross-sectional side view of a trigger mechanism  400  in a first configuration. In the first configuration, the trigger mechanism  400  can be in an unfired configuration in which a striker  402  is retained by the trigger mechanism  400  in a biased state. The trigger mechanism  400  can include a striker sear  404  which engages the striker  402  to retain the striker  402  in the biased state (e.g., the striker sear  404  can inhibit the striker  402  from launching toward a firing chamber of the barrel). The striker sear  404  and a main sear  406  can be coupled by a sear linkage  408 . The main sear  406  and a trigger  410  can engage with respective portions of a trigger sear  412 . The striker sear  404 , the main sear  406 , the trigger sear  412 , and the trigger  410  can each be rotatably coupled to a receiver or housing  414  by respective pins  416 ,  418 ,  420 ,  422 . 
     The striker sear  404  can be substantially similar to, and can include some or all of the features of, the striker sear  304 . For example, the striker sear  404  can be rotatably coupled to the housing  414  by the pin  416  such that a distal end  424  of the striker sear  404  can move into and out of contact with the striker  402 . The main sear  406  can be substantially similar to, and can include some or all of the features of, the main sear  306 . For example, the main sear  406  can include a distal end  426  which interfaces with a planar surface  428  formed on the trigger sear  412  to inhibit rotation of the main sear  406 . The sear linkage  408  can be substantially similar to, and can include some or all of the features of, the sear linkage  308 . For example, the sear linkage  408  can couple or interconnect the striker sear  404  and the main sear  406  while still enabling the striker sear  404  and the main sear  406  to rotate about respective pins  416 ,  418 . The trigger  410  can be substantially similar to, and can include some or all of the features of, the trigger  310 . For example, a user of the trigger mechanism  400  can rotate the trigger  410  about the pin  422  using an index finger (i.e., the user can pull the trigger  410 ) such that the trigger  410  engages with the trigger sear  412 . The trigger sear  412  can be substantially similar to, and can include some or all of the features of, the trigger sear  312 . For example, the trigger sear  412  can define the planar surface  428  which engages with the distal end  426  of the main sear  406 . 
     In some examples, the firing pin or striker  402  can be biased toward the barrel of the firearm. For example, the striker  402  can include or otherwise be coupled to a spring which biases the striker toward the barrel of the firearm. In the first configuration, the trigger mechanism  400  can retain the striker  402  in a position that is displaced from the barrel. For example, the distal end  424  of the striker sear  404  can be positioned adjacent the striker  402  as to contact or otherwise engage with the striker  402  to prevent the striker  402  from traveling toward the barrel. While displaced from the barrel, the spring or other biasing member can generate a force F 0 . The striker  402  can exert the force F 0  on the distal end  424  of the striker sear  404 . At least a portion of the force F 0  can be transferred through the sear linkage  408  to the main sear  406  to apply a force F 2 . The sear linkage  408  can be pivotably coupled to the striker sear  404  by a pin  430 , and can be pivotably coupled to the main sear  406  by a pin  432 . 
     At least a portion of the force F 2  can be exerted on the main sear  406  biasing the main sear  406  to rotate about the pin  418 . The force F 2  can be less than the force F 0 . At least a portion of the force F 2  can bias the main sear  406  to rotate about the pin  418 . While the force F 2  biases the main sear  406  to rotate about the pin  418 , the planar surface  428  of the trigger sear  412  can exert a force F 3  on the distal end  426  of the main sear  406 . A magnitude or value of the force F 3  can vary relative to the respective forces F 0 , F 1 , F 2  and their moment arms or distances (e.g., distances D 0 , D 1 , D 2 , along with the moment arm or distance D 3  shown in  FIG.  4 B ). For example, the force F 3  can correlate to a ratio including the distances D 0 , D 1 , D 2  D 3  and the force F 0 , as shown in Equation 4. The ratio can be at least about 0.05, between about 0.05 and about 0.1, between about 0.1 and about 0.5, between about 0.5 and about 0.7, or less than about 1. 
       FIG.  4 B  shows a cross-sectional side view of the trigger mechanism  400  in a second configuration. In the second configuration, the trigger mechanism  400  can be in a post-fired or post-actuated configuration in which the striker  402  has been released by the trigger mechanism  400  from the biased state shown in  FIG.  4 A . For example, when a user pulls the trigger  410  (e.g., exerts a force on the trigger  410  causing the trigger  410  to rotate about the pin  422 ), a portion  434  of the trigger  410  can engage a surface  436  of the trigger sear  412  to cause the trigger sear  412  to rotate about the pin  420  (as indicated by the rotational arrow  446  adjacent to the pin  420 ). Rotation of the trigger sear  412  about the pin  420  can pull or draw the planar surface  428  away from or out of contact with the distal end  426  of the main sear  406  such that the distal end  426  of the main sear  406  rotates toward the striker sear  404 . In some examples, the main sear  406  can be biased to rotate about the pin  418  by a spring  438  disposed around the pin  418  and contacting the main sear  406 . For example, the spring  438  can bias the main sear  406  to rotate about the pin  418  such that the main sear  406  is biased to return to an unfired position. In other words, the spring  438  can apply a biasing force on the main sear  406  which causes the main sear  406  to rotate back to the first configuration shown in  FIG.  4 A  wherein the distal end  426  of the main sear  406  is positioned to engage the planar surface  428  of the trigger sear  412 . 
     In some examples, the trigger sear  412  is rotated such that the planar surface  428  releases the main sear  406  to enable the main sear  406  to rotate about the pin  418  (as indicated by the rotational arrow  444  adjacent the pin  418 ). Rotation of the main sear  406  about the pin  418  can enable the sear linkage  408  to pivot relative to pins  430 ,  432 , and thereby release the distal end  424  of the striker sear  404  from engagement with the striker  402 . The striker sear  404  can be at least partially biased to engage the striker  402  by a spring  440 . For example, the spring  440  can interface with a protrusion  442  on the striker sear  404  and bias the striker sear  404  toward the striker  402 . The striker  402  can be driven by a spring or other biasing element (not shown) toward the barrel of the firearm when the striker sear  404  is disengaged from the striker  402 . 
     In another aspect of the present disclosure, trigger mechanisms are described which additionally, or alternatively, utilize one or more biasing members to provide a variable trigger pull weight. For example, one or more biasing members can engage a trigger sear, a trigger, another component, or a combination thereof to apply a force in resistance to its rotation when a trigger is pulled. In some examples, the one or more biasing members can be compressible and/or decompressible to vary (e.g., increase or decrease) the amount of force required to rotate the trigger sear and/or trigger. A first biasing member can be set such that a minimum pull weight is set and a second biasing member can be adjustable to increase or decrease the trigger pull weight to a value at or above the minimum pull weight set by the first biasing member. This aspect will be described in greater detail below with reference to  FIGS.  5 A- 6 B . 
       FIGS.  5 A and  5 B  show a trigger mechanism  500  including a biasing mechanism  502 , a trigger  504 , and a trigger sear  506 . In some examples, at least one component of the trigger mechanism  500  can be at least partially disposed within a housing  508 . The housing  508  can be configured to be releasably retained within a receiver of a firearm (e.g., the receiver  104  of the firearm  100 ). For example, the housing  508  can be fastened, clipped, pinned, or otherwise coupled within the receiver of the firearm. The biasing mechanism  502  can vary the amount of force required to pull the trigger  504  by biasing the trigger sear  506  to resist rotation when the trigger  504  is pulled. For example, the biasing mechanism  502  can include a first biasing member  510  and a second biasing member  512  which engage the trigger sear  506 . 
     In some examples, the first biasing member  510  can contact a first protrusion  514  extending from the trigger sear  506 . The second biasing member  512  can contact a second protrusion  516  extending from the trigger sear  506 . The first and second biasing members  510 ,  512  can be disposed within respective recesses  518 ,  520  formed by the housing  508 . In examples, the first biasing member  510  can be disposed within the recess  518  and between the first protrusion  514  of the trigger sear  506  and a first fastener  522 . Similarly, the second biasing member  512  can be disposed within the recess  520  and between the second protrusion  516  of the trigger sear  506  and a second fastener  524 . The first and second fasteners  522 ,  524  can be threadably received within the first and second recesses  518 ,  520 , of the housing  508 , respectively, such that each of the first and second fasteners  522 ,  524  can be repositionable within the respective recesses  518 ,  520  relative to the trigger sear  506 . For example, the first fastener  522  and/or the second fastener  524  can be rotated to travel toward or away from the trigger sear  506 , thereby compressing or decompressing the first biasing member  510  and/or second biasing member  512 , respectively. Compressing or decompressing one of the first or second biasing members  510 ,  512  can increase or decrease the force applied on the trigger sear  506  by the first or second biasing member  510 ,  512  and thereby vary a force required by a user to pull the trigger  504  (i.e., the trigger pull weight). 
     One or both of the first and second biasing members  510 ,  512  can be a spring, such as, a coiled spring which engages the trigger sear  506 . The first biasing member  510  can have a spring constant greater than, less than, or equivalent to a spring constant of the second biasing member  512 . In some examples, the spring constant of the first biasing member  510  can be larger than the spring constant of the second biasing member  512  such that the first biasing member  510  is stiffer than the second biasing member  512 . Accordingly, in these examples, the first biasing member  510  can apply a greater force on the trigger sear  506  as the first fastener  522  is rotated to move toward the trigger sear  506  than the force applied on the trigger sear  506  by the second biasing member  512  as the second fastener  524  is rotated to move toward the trigger sear  506 . In some examples, the spring constant of the second biasing member  512  can be larger than the spring constant of the first biasing member  510  such that the second biasing member  512  is stiffer than the first biasing member  510 . Accordingly, in these examples, the second biasing member  512  can apply a greater force on the trigger sear  506  as the second fastener  524  is rotated to move toward the trigger sear  506  than the force applied on the trigger sear  506  by the first biasing member  510  as the first fastener  522  is rotated to move toward the trigger sear  506 . 
     The trigger sear  506  can rotate about a pin  526  coupled to the housing  508 . The first biasing member  510  can contact the trigger sear  506  at a distance D 1  from the pin  526 . The second biasing member  512  can contact the trigger sear  506  at a distance D 2  from the pin  526 . In some examples, the first protrusion  514  can engage the first biasing member  510  to cause the first biasing member  510  to contact the trigger sear  506  at the distance D 1 . In some examples, the second protrusion  516  can engage the second biasing member  512  to cause the second biasing member  512  to contact the trigger sear  506  at the distance D 2 . The distance D 1  can be greater than the distance D 2 , for example, the distance D 1  can be at or between about 1.5 and about 3 times greater than the distance D 2 . 
       FIG.  5 C  shows a bottom perspective view of the biasing mechanism  502  of the trigger mechanism  500 . The first fastener  522  can include an engagement structure  528 , such as, a recess defining a particular shape configured to engage a tool (not shown) to enable a user to rotate the first fastener  522  relative to the housing  508  (e.g., toward and away from the trigger sear  506 ). The second fastener  524  can include an engagement structure  530 , such as, a recess defining a particular shape configured to engage a tool (not shown) to enable a user to rotate the second fastener  524  relative to the housing  508  (e.g., toward and away from the trigger sear  506 ). For example, one or both of the engagement structures  528 ,  530  can be shaped to receive a portion of a tool, such as, a wrench, a screwdriver, and/or another tool. In some examples, at least one of the engagement structures  528 ,  530  can define a hexagonal shaped recess configured to receive an Allen wrench or another tool having a hexagonal shaped tool head. While  FIG.  5 C  depicts engagement structures  528 ,  530  defining hexagonal shaped recesses, the shape and profile of each engagement structure  528 ,  530  can define any shape, profile, or form that interfaces or otherwise engages with a tool. 
     The first fastener  522  and/or the second fastener  524  can at least partially extend from an exterior surface  532  of the housing  508 , or otherwise be accessible through the housing  508 , to enable rotation of the first fastener  522  and/or second fastener  524  without deconstructing the trigger mechanism  500  (e.g., removing a portion of the housing  508 ). In some examples, at least one of the engagement structures  528 ,  530  can be accessible by a tool while the trigger mechanism  500  is disposed within the receiver (e.g., receiver  104 ) such that the user is not required to remove the trigger mechanism  500  from the firearm to rotate the first and/or second fasteners  522 ,  524 . In some examples, at least one of the engagement structures  528 ,  530  can be accessible only while the trigger mechanism  500  is removed from the receiver (e.g., receiver  104 ). For example, at least one of the engagement structures  528 ,  530  can be covered or hidden by another component of the firearm, such as, a stock, a trigger guard, a decal, a combination thereof, or another component of the firearm. 
       FIG.  5 D  shows an example having the biasing mechanism  502  disposed at a different location or position on the housing  508 . In this example, the biasing mechanism  502  can vary the amount of force required to pull the trigger  504  by biasing the trigger  504  to resist rotation when the trigger  504  is pulled. For example, the first biasing member  510  and the second biasing member  512  can exert a force on the trigger  504  which can be modified by rotating the first and/or second fasteners. The examples shown in  FIGS.  5 A- 5 C and  5 D  are merely two example applications of many application in which the biasing mechanism  502  exerts a force on the trigger mechanism  500 . In some examples, the biasing mechanism  502  can engage or otherwise bias other components or multiple components of the trigger system  500 . For example, one example (not shown) can include a first biasing mechanism applied as shown in  FIG.  5 A  and a second biasing mechanism applied as shown in  FIG.  5 D . Additionally, or alternatively, the biasing mechanism  500  can have more or fewer biasing members than the first and second biasing members  510 ,  512  shown in  FIGS.  5 A- 5 D . 
     In some examples, the first biasing member  510  can contact a first protrusion  514  extending from the trigger  504 . The second biasing member  512  can contact a second protrusion  516  extending from the trigger  504 . The first and second biasing members  510 ,  512  can be disposed within respective recesses  518 ,  520  formed by the housing  508 . In examples, the first biasing member  510  can be disposed within the recess  518  and between the first protrusion  514  of the trigger  504  and the first fastener  522 . Similarly, the second biasing member  512  can be disposed within the recess  520  and between the second protrusion  516  of the trigger  504  and the second fastener  524 . The first and second fasteners  522 ,  524  can be threadably received within the first and second recesses  518 ,  520 , of the housing  508 , respectively, such that each of the first and second fasteners  522 ,  524  can be repositionable within the respective recesses  518 ,  520  relative to the trigger  504 . For example, the first fastener  522  and/or the second fastener  524  can be rotated to travel toward or away from the trigger  504 , thereby compressing or decompressing the first biasing member  510  and/or second biasing member  512 , respectively. Compressing or decompressing one of the first or second biasing members  510 ,  512  can increase or decrease the force applied on the trigger  504  by the first or second biasing member  510 ,  512  and thereby vary a force required by a user to pull the trigger  504  (i.e., the trigger pull weight). 
     One or both of the first and second biasing members  510 ,  512  can be a spring, such as, a coiled spring which engages the trigger  504 . The first biasing member  510  can have a spring constant greater than, less than, or equivalent to a spring constant of the second biasing member  512 . In some examples, the spring constant of the first biasing member  510  can be larger than the spring constant of the second biasing member  512  such that the first biasing member  510  is stiffer than the second biasing member  512 . Accordingly, in these examples, the first biasing member  510  can apply a greater force on the trigger  504  as the first fastener  522  is rotated to move toward the trigger  504  than the force applied on the trigger  504  by the second biasing member  512  as the second fastener  524  is rotated to move toward the trigger  504 . In some examples, the spring constant of the second biasing member  512  can be larger than the spring constant of the first biasing member  510  such that the second biasing member  512  is stiffer than the first biasing member  510 . Accordingly, in these examples, the second biasing member  512  can apply a greater force on the trigger  504  as the second fastener  524  is rotated to move toward the trigger  504  than the force applied on the trigger  504  by the first biasing member  510  as the first fastener  522  is rotated to move toward the trigger  504 . 
       FIGS.  6 A- 6 F  show partial bottom views of a trigger mechanism  600  including examples of fasteners having various engagement structures.  FIG.  6 A  shows the trigger mechanism  600  including a biasing mechanism  602 , a trigger  604 , and a trigger sear  606 . In examples, at least one component of the trigger mechanism  600  can be at least partially disposed within a housing  608 . The housing  608  can be configured to be coupled to or at least partially disposed within a receiver of a firearm (e.g., the receiver  104  of the firearm  100 ). For example, at least a portion of the housing  608  can be fastened, clipped, pinned, or otherwise coupled to the receiver of the firearm. The biasing mechanism  602  can be substantially similar to, and can include some or all of the features of, the biasing mechanism  502 . For example, the biasing mechanism  602  can vary the amount of force required to pull the trigger  604  by biasing the trigger sear  606  to resist rotation when the trigger  604  is pulled. The biasing mechanism  602  can include a first biasing member (e.g., the biasing member  510 ) and a second biasing member (e.g., the biasing member  512 ) which engage the trigger sear  606 . The first and second biasing members (not shown) can be retained within respective apertures or recesses (e.g., recesses  518 ,  520 ) formed within the housing  608 . The first and second biasing members can be retained within the apertures or recesses by first and second fasteners  622 ,  624 , respectively. 
     The biasing mechanism  602  can set a pull weight of the trigger  604  to a particular value within a range of values. Furthermore, the biasing mechanism  602  can set a minimum trigger pull weight (i.e., a lowest amount of force required to pull the trigger) within the range of values. A manufacturer of firearms, for example, can desire to set the minimum trigger pull weight value at the factory before shipping the firearm to a distributor or consumer. 
     In some examples, a manufacturer of firearms or trigger mechanisms can remove the second fastener  624  or otherwise rotate the second fastener  624  such that the second biasing member is no longer exerting a force on the trigger sear  606 . Thereafter, the manufacturer can rotate (e.g., clockwise or counterclockwise) the first fastener  622  until a desired minimum force required to pull the trigger  604  is set (i.e., the first biasing member can apply a force on the trigger sear  606  that requires a desired minimum trigger pull weight at the trigger  604  before the trigger sear  606  will disengage from the main sear). The first fastener  622  can then be obstructed or rendered inaccessible such that subsequent persons are prevented from rotating the first fastener  622  to vary the desired minimum force set by the manufacturer. Accordingly, because the second fastener  624  is rotated such that the second biasing member is not applying a force on the trigger sear  606  before the first fastener  622  is set, subsequent rotation of the second fastener  624  may only increase the amount of force required to pull the trigger  604 , not decrease the amount of force required to pull the trigger  604 . In other words, the force applied on the trigger sear  606  by the first biasing member can act as a base line or minimum value for the trigger pull weight and subsequent force placed on the trigger sear  606  by the second biasing member can only increase the trigger pull weight from the baseline or minimum value. 
     While the minimum trigger pull weight is described as being set by the first fastener  622  herein, the second fastener  624  can alternatively be utilized to set the minimum trigger pull weight of the trigger mechanism  600 . For example, the manufacturer can remove the first fastener  622  or otherwise rotate the first fastener  622  such that the first biasing member is no longer exerting any force on the trigger sear  606 , and thereafter, the manufacturer can rotate (e.g., clockwise or counterclockwise) the second fastener  624  until the desired minimum force required to pull the trigger  604  is set. Thereafter, the manufacturer can obstruct or render the second fastener  624  inaccessible to prevent future adjustment of the second fastener  624  and the resultant minimum value set by the manufacturer. 
     The biasing mechanism  602  can include one or more components or features which prevent or inhibit adjustment of the first fastener  622  after the minimum trigger pull weight value is set. For example, as shown in  FIG.  6 A , the first fastener  622  can be subsequently covered by a cap  626  (illustrated as transparent in  FIG.  6 A ). The cap  626  can be disposed within a recess (e.g., recess  518 ) defined by the housing  608  to cover or otherwise obstruct access to the first fastener  622 . The cap  626  can be affixed within the recess by an interference fit, an adhesive, a threaded connection, a magnetic connection, another coupling mechanism, or a combination thereof. The cap  626  can be manufactured from a metal, a polymer, a ceramic, or a combination thereof. In examples, the cap  626  can be flush with an exterior surface  628  of the housing  608 . 
     The first fastener  622  and/or second fastener  624  of the biasing mechanism  602  can include respective engagement structures  630 ,  632  which prevent or inhibit adjustment of the first fastener  622  and/or the second fastener  624  without a particular tool. In other words, one or both of the first and second fasteners  622 ,  624  can include engagement structures  630 ,  632  that define tamper proof interfaces. For example, as shown in  FIG.  6 B , the first fastener  622  can include an engagement structure  630  which necessitates a tool having a security head having multiple prongs to engage first and second blind holes  634 A,  634 B defined by the engagement structure  630  to rotate the first fastener  622 . The security head required to rotate the first fastener  622  can be uncommon and thereby limit or inhibit a user from rotating the first fastener  622  after a desired minimum trigger pull weight is set. Additionally, or alternatively, the second fastener  624  can include an engagement structure  632  which necessitates a tool having a security head to rotate the second fastener  624 . The security head required to rotate the second fastener  624  can be uncommon and thereby limit or inhibit a user from rotating the second fastener  624  after a desired minimum trigger pull weight is set. 
     While the engagement structure  630  defines first and second blind holes  634 A,  634 B, any known or subsequently discovered security interface pattern can be defined by the engagement structure  630 . For example, the engagement structure  630  and/or engagement structure  632  can define a torx style recess, a clutch style recess, a fluted socket style recess, a tri-wing recess, a square recess, a  5  or  7  node security recess, a hexagonal recess, a spanner drilled recess, a spanner slotted recess, a combination thereof, or any other security type recess. Furthermore, the engagement structure  630  can define a pillar or central column commonly formed within tamper proof bolt heads. 
       FIGS.  6 C- 6 F  show another example of the trigger mechanism  600  including a first fastener  622  having a removable portion  636 . As shown in  FIGS.  6 C and  6 D , a manufacturer can insert the first fastener  622  into a threaded recess  638  using a tool  640  or other object to rotate the first fastener  622  within the recess  638  to a desired position within the recess  638  (i.e., setting or establishing the minimum trigger pull weight of the trigger mechanism  600  as described herein). While a flat head screwdriver and a correlating slot on the removable portion  636  are shown in  FIGS.  6 C and  6 D , any other type of tool and correlating interface can be employed. Additionally, or alternatively, a thumb and a finger can be engaged on the removal portion  636  to rotate the first fastener  622  into or out of the recess  638 . 
     As shown in  FIGS.  6 E and  6 F , after the first fastener  622  has been disposed at the desired position within the recess  638 , the removable portion  636  of the first fastener  622  can be removed or broken away from the first fastener  622  to prevent subsequent persons from altering the position of the first fastener  622  and thereby manipulating the baseline or minimum trigger pull weight set by the manufacturer. In some examples, the removable portion  636  can be retained to a body  642  of the first fastener  622  by a thinned section  644 . The thinned section  644  can be cracked, cut, or broken to enable separation of the removable portion  636  from the body  642  of the first fastener  622 . 
     In some examples, the endpoint values disclosed herein may be approximate values, which may vary by 10% or less from the precise endpoint value given. In such examples, the term “about” or “substantially” may indicate the approximate values. 
     Aspects of any of the examples disclosed herein may be used with aspects of any other examples, disclosed herein without limitation. 
     While various aspects and embodiments have been disclosed herein, other aspects and embodiments are contemplated. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting. Additionally, the words “including,” “having,” and variants thereof (e.g., “includes” and “has”) as used herein, including the claims, shall be open ended and have the same meaning as the word “comprising” and variants thereof (e.g., “comprise” and “comprises”).