Patent Publication Number: US-11385011-B2

Title: Modular trigger control unit for firearms

Description:
CROSS REFERENCE TO RELATED PATENT APPLICATION(S) 
     The present disclosure is part of a continuation-in-part (CIP) of U.S. patent application Ser. No. 16/726,923, filed on 25 Dec. 2019, which is a CIP of U.S. patent application Ser. No. 16/718,825, filed on 18 Dec. 2019 and issued as U.S. Pat. No. 10,837,727 on 17 Nov. 2020, which claims the priority benefit of U.S. Provisional Patent Application No. 62/781,238, filed on 18 Dec. 2018. Contents of aforementioned applications are incorporated by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure is generally related to firearms and, more particularly, to a modular trigger control unit for firearms. 
     BACKGROUND 
     Unless otherwise indicated herein, approaches described in this section are not prior art to the claims listed below and are not admitted as prior art by inclusion in this section. 
     To enhance customization of firearms, modular systems have been introduced to the market for rifles, carbines and pistols alike. However, for pistols such as semi-automatic pistols, currently available modular systems are proprietary in that a fire control unit of a given vendor is designed to function only with proprietary grip frames and slide assemblies. 
     SUMMARY 
     The following summary is illustrative only and is not intended to be limiting in any way. That is, the following summary is provided to introduce concepts, highlights, benefits and advantages of the novel and non-obvious techniques described herein. Select implementations are further described below in the detailed description. Thus, the following summary is not intended to identify essential features of the claimed subject matter, nor is it intended for use in determining the scope of the claimed subject matter. 
     An objective of the present disclosure is to provide a modular trigger control unit that can be installed on and function with a plurality of grip frames and slide assemblies of different sizes, colors and/or calibers to form a semi-automatic or full-automatic (e.g., striker-fired) firearm. With the identification marking of the firearm is displayed on the trigger control unit, the modular trigger control unit enables firearm customization by a user. 
     In one aspect, an apparatus (e.g., a semi-automatic or full-automatic firearm) may include a trigger control unit configured to be removably installed on a grip frame of a firearm. The trigger control unit may include a locking block and a locking block pin. The trigger control unit may have a protruding tab protruding rearward with respect to the firearm. The locking block may include a pair of slide rails extending forward with respect to the firearm, with each slide rail of the pair of slide rails having a flat wall extending downward with respect to the grip frame when the trigger control unit is installed on the grip frame. Accordingly, the trigger control unit may be secured to the grip frame by: (1) the protruding tab received in a recess on an interior wall of a beavertail portion of the grip frame; and (2) the locking block pin traversing through a through hole on the flat wall extending from each slide rail of the pair of slide rails such that removal of the trigger control unit from the grip frame requires removal of the locking block pin. 
     In another aspect, an apparatus (e.g., a semi-automatic or full-automatic firearm) may include a trigger control unit configured to be removably received in a grip frame of a firearm and installed between the grip frame and a slide assembly of the firearm such that, when activated, the trigger control unit causes firing of one or more rounds of ammunition. The trigger control unit may include a trigger mechanism housing, a trigger pin, a trigger pivotable around the trigger pin when pulled, a trigger bar coupled between the trigger and the trigger mechanism housing, a locking block, a locking block pin, and a support frame having a first distal end and a second distal end opposite the first distal end such that the first distal end faces a front side of the grip frame and the second distal end faces a back side of the grip frame when the trigger control unit is installed on the grip frame. The locking block may include a pair of slide rails extending forward with respect to the trigger and the firearm, with each slide rail of the pair of slide rails having a flat wall extending downward with respect to the grip frame when the trigger control unit is installed on the grip frame. Accordingly, the trigger control unit may be secured to the grip frame by at least the locking block pin such that removal of the trigger control unit from the grip frame requires removal of the locking block pin. 
     In yet another aspect, an apparatus (e.g., a semi-automatic or full-automatic firearm) may include a trigger mechanism housing configured to be removably received in a grip frame of a firearm such that, when received in the grip frame, a serial number of the firearm displayed on the trigger mechanism housing may coincide with a centerline of a back side of the grip frame. 
     It is noteworthy that, although description provided herein may be in the context of certain type of semi-automatic or full-automatic firearms such as a striker-fired pistol, the proposed concepts, schemes and any variation(s)/derivative(s) thereof may be implemented in, for and by other types of firearms such as, for example and without limitation, hammer-fired semi-automatic pistols, other semi-automatic firearms and automatic firearms. Thus, the scope of the present disclosure is not limited to the examples described herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the disclosure, and are incorporated in and constitute a part of the present disclosure. The drawings illustrate implementations of the disclosure and, together with the description, serve to explain the principles of the disclosure. It is appreciable that the drawings are not necessarily in scale as some components may be shown to be out of proportion than the size in actual implementation in order to clearly illustrate the concept of the present disclosure. 
         FIG. 1  is a diagram of an exploded view of some of the components of a firearm in accordance with an implementation of the present disclosure. 
         FIG. 2  is a diagram of a firearm in accordance with an implementation of the present disclosure. 
         FIG. 3  is a diagram of an assembly of a portable trigger control unit in accordance with an implementation of the present disclosure. 
         FIG. 4  is a diagram of an exploded view of a portable trigger control unit in accordance with an implementation of the present disclosure. 
         FIG. 5  is a diagram of major components of a firearm in accordance with an implementation of the present disclosure. 
         FIG. 6  is a diagram showing a perspective view of a portable trigger control unit in accordance with an implementation of the present disclosure installed on grip frames for different calibers of ammunition. 
         FIG. 7  is a diagram showing a back view of a portable trigger control unit in accordance with an implementation of the present disclosure installed on grip frames for different calibers of ammunition. 
         FIG. 8  is a diagram of a grip frame of a firearm in accordance with an implementation of the present disclosure. 
         FIG. 9  is a diagram of an exploded view of some of the components of a firearm in accordance with an implementation of the present disclosure. 
         FIG. 10  is a diagram of another exploded view of some of the components of the firearm of  FIG. 9 . 
         FIG. 11  is a diagram showing a perspective view of a portable trigger control unit installed on a grip frame of the firearm of  FIG. 9 . 
         FIG. 12  is a diagram of an exploded view of some of the components of a firearm in accordance with an implementation of the present disclosure. 
         FIG. 13  is a diagram of another exploded view of some of the components of the firearm of  FIG. 12 . 
         FIG. 14  is a diagram showing a perspective view of a portable trigger control unit installed on a grip frame of the firearm of  FIG. 12 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED IMPLEMENTATIONS 
     Detailed embodiments and implementations of the claimed subject matters are disclosed herein. However, it shall be understood that the disclosed embodiments and implementations are merely illustrative of the claimed subject matters which may be embodied in various forms. The present disclosure may, however, be embodied in many different forms and should not be construed as limited to the exemplary embodiments and implementations set forth herein. Rather, these exemplary embodiments and implementations are provided so that description of the present disclosure is thorough and complete and will fully convey the scope of the present disclosure to those skilled in the art. In the description below, details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the presented embodiments and implementations. 
     Overview 
     Under various proposed schemes in accordance with the present disclosure, a portable trigger control unit offers modularity and a great degree of customization of firearms such as, for example, semi-automatic or full-automatic pistols. The trigger control unit may be utilized with different grip frames of different sizes and/or colors as well as different slide assemblies of different sizes, colors and/or calibers. It is noteworthy that, although examples in the present disclosure are provided in the context of a striker-fired pistol, the proposed schemes in accordance with the present disclosure may be implemented in different types of firearms (e.g., hammer-fired pistols or semi-automatic rifles and carbines). 
     Illustrative Implementations 
       FIG. 1  illustrates some of the components of a firearm  50  in accordance with an implementation of the present disclosure. Referring to  FIG. 1 , firearm  50  may include a portable firing control unit or trigger control unit  100  and a grip frame  200 . Under the proposed schemes, an identification marking of firearm  50  may be displayed on a portion (e.g., right side or left side) of trigger control unit  100  so that, when the trigger control unit  100  is received, mounted, seated or otherwise installed in a hollow of grip frame  200  the identification marking of firearm  50  may be visible through a cutout or opening on grip frame  200  on the same side (e.g., right side or left side) of trigger control unit  100  where the identification marking is displayed. Grip frame  200  may be made of a polymeric material. Alternatively, grip frame  200  may be made of metal or a composite of metal and polymer. Firearm  50 , or trigger control unit  100 , may also include a trigger pin  190 , a locking block pin  192  and a trigger housing pin  194 . 
     Trigger control unit  100  may be removably installed on or otherwise removably received in grip frame  200 . Accordingly, at any given time, a user may install the same trigger control unit  100  in one of different grip frames of different or same colors or for different or same calibers. For instance, a user may install the same trigger control unit  100  in a grip frame in black color for a pistol chambered in 9 mm caliber, in a grip frame in flat dark earth (FDE) color for another pistol chambered in 9 mm (or 40S&amp;W or 357 Sig) caliber, or in a grip frame for a pistol chambered in 45ACP (or 10 mm) caliber. 
     Trigger control unit  100  may be secured to grip frame  200  at least by trigger pin  190  such that removal of trigger control unit  100  from grip frame  200  would require removal of trigger pin  190  first. In some cases, trigger control unit  100  may also be secured to grip frame  200  by trigger housing pin  194  and/or locking block pin  192 . 
       FIG. 2  illustrates firearm  50  in accordance with an implementation of the present disclosure. Referring to  FIG. 2 , in addition to trigger control unit  100  and grip frame  200 , firearm  50  may also include a slide assembly  300 . Trigger control unit  100  may be installed between grip frame  200  and slide assembly  300 . In the example shown in  FIG. 2 , slide assembly  300  may contain a striker-firing mechanism  350  (shown in  FIG. 3 ), a barrel and a recoil spring assembly therein. 
       FIG. 3  illustrates an assembly of portable trigger control unit  100  in accordance with an implementation of the present disclosure. Referring to  FIG. 3 , in addition to trigger pin  190 , locking block pin  192  and trigger housing pin  194 , trigger control unit  100  may also include a trigger  110 , a trigger mechanism housing  120 , a trigger bar  130 , a support frame  140 , and a locking block  150  with a pair of slide rails  150 A and  150 B. 
     Trigger  110  may be pivotable around trigger pin  190  when pulled by a user. In response to trigger  110  being pulled by the user when trigger control unit  100  is installed between grip frame  200  and slide assembly  300 , a firing pin lug  360  of the striker-firing mechanism  350  in slide assembly  300  may be released thereby allowing a striker  370  of the striker-firing mechanism  350  to move forward with respect to slide assembly  300 . Thus, a user can grip the grip frame  200  and squeeze trigger  110  of trigger control unit  100 , among other actions, to fire a round of ammunition. 
     Trigger bar  130  may be coupled between trigger  1110  and the trigger mechanism housing  120 . In response to trigger  110  being pulled by the user when trigger control unit  100  is installed between grip frame  200  and slide assembly  300 , trigger bar  130  may cause a sear in the trigger mechanism housing to lower relative to slide assembly  300  such that the firing pin lug is released (e.g., to strike the primer of a round of ammunition if the round is chambered). 
     Support frame  140  may have a first distal end (e.g., front) and a second distal end (e.g., back) opposite the first distal end. Trigger  110  may be pivotably coupled to the first distal end of support frame  140  with trigger pin  190  traversing through trigger  110  and the first distal end of support frame  140 . Moreover, trigger mechanism housing  120  may be coupled to the second distal end of support frame  140 . Support frame  140  may be made of a polymeric material, metal or a composite of metal and polymer. 
     The pair of slide rails  150 A and  150 B of locking block  150  may extend forward and protrude from a front side of support frame  140  with respect to firearm  50 . When trigger control unit  100  is installed between grip frame  200  and the slide assembly  300 , slide assembly  300  may be movable forwardly and rearwardly with respect to grip frame  200  on the slide rails  150 A and  150 B. 
     In terms of modularity and customization, trigger control unit  100  may be configured to be removably installed on or otherwise removably received in each of a plurality of grip frames and installed between each of the plurality of grip frames and each of a plurality of slide assemblies such that: (a) at least two of the plurality of grip frames have different sizes (e.g., full, carry, compact and subcompact), different colors (e.g., black, flat dark earth (FDE), olive drab (OD) and grey), or different sizes and colors, and/or (b) at least two of the plurality of slide assemblies have different sizes, different colors, different calibers, or any combination thereof. 
       FIG. 4  illustrates an exploded view of portable trigger control unit  100  in accordance with an implementation of the present disclosure.  FIG. 5  illustrates major components of firearm  50  in accordance with an implementation of the present disclosure. 
     Referring to  FIG. 4  and  FIG. 5 , trigger control unit  100  may be removably received in grip frame  200  of a semi-automatic (or full-automatic) firearm  50  and may be installed between grip frame  200  and slide assembly  300  of firearm  50 . Slide assembly  300  may contain a striker-firing mechanism and may be longitudinally movable (e.g., forwardly and rearwardly) on grip frame  200  when slide assembly  300  is installed on grip frame  200  with trigger mechanism housing  120  installed between slide assembly  300  and grip frame  200 . Accordingly, when activated, trigger control unit  100  may cause firing of one or more rounds of ammunition. Under a proposed design in accordance with the present disclosure, and as described above, trigger control unit  100  may include at least the following major components: a trigger mechanism housing  120 , a trigger pin  190 , a trigger  110  that is pivotable around trigger pin  190  when pulled, a trigger bar  130  coupled between trigger  110  and trigger mechanism housing  120 , a locking block  150 , and a support frame  140 . Support frame  140  may have a first distal end (e.g., front end) and a second distal end (e.g., back end) opposite the first distal end such that the first distal end faces a front side of grip frame  200  and the second distal end faces the back side of grip frame  200  when trigger control unit  100  is installed on or otherwise received in grip frame  200 . The back side of grip frame  200  is the side of grip frame  200  that is opposite, or 180° from, a muzzle of firearm  50  and faces toward a user of firearm  50 . 
     Under the proposed design, an identification marking  60  of firearm  50  (e.g., one or more of the following: a serial number, a caliber, a model name or number, and a name of a manufacturer) may be displayed on trigger mechanism housing  120 . For instance, identification marking  60  may be displayed on a back surface of trigger mechanism housing  120  which faces a back side of grip frame  200  along a centerline  210  of the back side of grip frame  200  when trigger mechanism housing  120  is received in or otherwise installed on grip frame  200 . Centerline  210  is a line with an equal distance to each of the left side and the right side of grip frame  200  when viewed from the back side of grip frame  200 . Accordingly, when trigger mechanism housing  120  is received in grip frame  200 , identification marking  60  of firearm displayed  50 , which is displayed on and along centerline  210  of the back side of trigger mechanism housing  120 , can be visible through an opening  205  on a back side of grip frame  200 . As identification marking  60  is displayed on trigger mechanism housing  120 , under current United States laws and regulations, trigger mechanism housing  120  itself may be considered as a firearm. 
     Under the proposed design, trigger mechanism housing  120  may be configured to be removably received in each of a plurality of grip frames and installed between each of the plurality of grip frames and each of a plurality of corresponding slide assemblies. Under the proposed design, at least two of the plurality of grip frames may have different sizes, different colors, or different sizes and colors. Alternatively, at least two of the plurality of slide assemblies may have different sizes, different colors, different calibers, or any combination thereof. 
     Under the proposed design, in response to trigger  110  being pulled by a user when trigger control unit  100  is installed between grip frame  200  and slide assembly  300 , a firing pin lug of a striker-firing mechanism in slide assembly  300  may be released thereby allowing a striker of the striker-firing mechanism to move forward with respect to slide assembly  300 . Additionally, trigger control unit  100  may be secured to grip frame  200  at least by trigger pin  190  such that removal of trigger control unit  100  from grip frame  200  requires removal of trigger pin  190 . Also, in response to trigger  110  being pulled by the user when trigger control unit  100  is installed between grip frame  200  and slide assembly  300 , trigger bar  130  may cause a sear in trigger mechanism housing  120  to lower relative to slide assembly  300  such that the firing pin lug is released. Moreover, trigger  110  may be pivotably coupled to the first distal end of support frame  140  with trigger pin  190  traversing through trigger  110  and the first distal end of support frame  140 . In such cases, trigger mechanism housing  120  may be coupled to the second distal end of support frame  140 . Furthermore, locking block  150  may include a pair of slide rails  150 A and  150 B extending forward from support frame  140  with respect to grip frame  200  as well as firearm  50 . In such cases, when trigger control unit  100  is installed between grip frame  200  and slide assembly  300 , slide assembly  300  may be movable longitudinally (e.g., forwardly and rearwardly) with respect to grip frame  200  on the slide rails. 
     Under the proposed design, support frame  140  may be made of a polymeric material, metal or a composite of metal and polymer. Under the proposed design, each of trigger mechanism housing  120  and support frame  140  may be configured with physical features that allow support frame  140  to be snapped onto trigger mechanism housing  120  to be physically or otherwise mechanically coupled to each other. For instance, trigger mechanism housing  120  may be configured with a left indentation on a left side thereof and a right indentation (which is identified by numeral reference  125  in  FIG. 4 ) on a right side thereof. Moreover, support frame  140  may be configured with a left protrusion (which is identified by numeral reference  145  in  FIG. 4 ) on a left inner surface near the second distal end and a right protrusion on a right inner surface near the second distal end. In such cases, support frame  140  may be coupled to trigger mechanism housing  120  by the left protrusion received in the left indentation and the right protrusion received in the right indentation. Alternatively, trigger mechanism housing  120  may be configured with a left protrusion on a left side thereof and a right protrusion on a right side thereof. Moreover, support frame  140  may be configured with a left indentation on a left inner surface near the second distal end and a right indentation on a right inner surface near the second distal end. In such cases, support frame  140  may be coupled to trigger mechanism housing  120  by the left protrusion received in the left indentation and the right protrusion received in the right indentation. 
       FIG. 6  illustrates a perspective view of a portable trigger control unit in accordance with an implementation of the present disclosure installed on grip frames for different calibers of ammunition.  FIG. 7  illustrates a back view of a portable trigger control unit in accordance with an implementation of the present disclosure installed on grip frames for different calibers of ammunition. 
     For illustrative purposes and without limiting the scope of the present disclosure, part (A) of each of  FIG. 6  and  FIG. 7  shows a portable trigger control unit  100 A installed on or otherwise received in grip frame  200 A which is dimensioned or otherwise configured for calibers such as 9 mm, 40S&amp;W and/or 357 Sig. Similarly, part (B) of each of  FIG. 6  and  FIG. 7  shows a portable trigger control unit  100 B installed on or otherwise received in grip frame  200 B which is dimensioned or otherwise configured for calibers such as 45ACP and/or 10 mm. That is, the size of grip frame  200 B may be larger than the size of grip frame  200 A in one or more dimensions. 
     As shown in part (A) of  FIG. 6 , portable trigger control unit  100 A may include major components such as trigger  110 A, trigger mechanism housing  120 , trigger bar  130 A, support frame  140 A and locking block  150 A. As shown in part (B) of  FIG. 6 , portable trigger control unit  100 B may include major components such as trigger  110 B, trigger mechanism housing  120 , trigger bar  130 B, support frame  140 B, and locking block  150 B. Although denoted differently, dimensions of trigger  110 A and trigger  110 B may be identical or different, dimensions of trigger bar  130 B and trigger bar  130 B may be identical or different, dimensions of support frame  140 A and support frame  140 B may be identical or different, and dimensions of locking block  150 A and locking block  150 B may be identical or different. In any event, under the proposed scheme, there is no need to change trigger mechanism housing  120  when changing grip frame, slide assembly and/or one or more other components of portable trigger control unit. That is, for modularity, except for trigger mechanism housing  120 , some or all other components may be changed for different sizes, different colors and/or different calibers. 
     It is noteworthy that each of trigger  110 , trigger  110 A and trigger  1108  may be identical to each other or may differ in one or more dimensions from each other and, thus, descriptions herein with respect to trigger  110  are applicable to trigger  110 A and trigger  110 B. Similarly, each of trigger bar  130 , trigger bar  130 A and trigger bar  130 B may be identical to each other or may differ in one or more dimensions from each other and, thus, descriptions herein with respect to trigger bar  130  are applicable to trigger bar  130 A and trigger bar  130 B. Likewise, each of support frame  140 , support frame  140 A and support frame  140 B may be identical to each other or may differ in one or more dimensions from each other and, thus, descriptions herein with respect to support frame  140  are applicable to support frame  140 A and support frame  140 B. 
     Advantageously, a user may purchase portable trigger control unit  100  (or just trigger mechanism housing  120  alone), which may be registered as a “firearm” since the identification marking  60  (e.g., serial number) is displayed on and along centerline  210 , or otherwise coincides with centerline  210 , of the back side of trigger mechanism housing  120 , and the user may modularly customize the configuration of firearm  50  by utilizing the trigger control unit  100  (or trigger mechanism housing  120 ) with different grip frames, different slide assemblies and/or different barrels, with or without one or more components of trigger control unit  100  changed to a different size (except trigger mechanism housing  120 , which can remain unchanged from one configuration to another). 
     As shown in part (A) of  FIG. 7 , grip frame  200 A may be configured with an opening or cutout on and along centerline  210  of the back side (e.g., facing back or rearward with respect to firearm  50  from a user&#39;s perspective) with a location aligned with or otherwise corresponding to a location of the identification marking  60  (e.g., serial number) of firearm  50  displayed on the back side of trigger mechanism housing  120 . Similarly, as shown in part (B) of  FIG. 7 , grip frame  200 B may be configured with an opening or cutout on and along centerline  210  of the back side thereof (e.g., facing back or rearward with respect to firearm  50  from a user&#39;s perspective) with a location aligned with or otherwise corresponding to a location of the identification marking  60  (e.g., serial number) of firearm  50  displayed on the back side of trigger mechanism housing  120 . 
       FIG. 8  illustrates grip frame  200  of firearm  50  in accordance with a proposed design of the present disclosure. Each of  FIG. 9 ,  FIG. 10  and  FIG. 11  illustrates a respective view of some of the components of firearm  50  in accordance with a proposed design of the present disclosure. Referring to  FIG. 8  and  FIG. 9 ˜ FIG. 11 , grip frame  200  may have a beavertail portion  248  at the back end thereof. That is, beavertail portion  248  may protrude rearward (e.g., toward a user when firearm  50  is held by the user). Under a proposed design, an interior wall of beavertail portion  248  may be configured with an indentation or recess  220  which may be configured, sized or otherwise dimensioned to receive a protruding tab  148  of trigger control unit  100 . 
     Under a proposed design, protruding tab  148  may be formed by a rearward protrusion of trigger mechanism housing  120 , which may be made of a metal. Under another proposed design, protruding tab  148  may be formed by a rearward protrusion of support frame  140 , which may be made of polymer. Under yet another proposed design, protruding tab  148  may be partially formed by a rearward protrusion of trigger mechanism housing  120  and partially formed by a rearward protrusion of support frame  140 . That is, in this design, protruding tab  148  may be a composite of metal and polymer (e.g., partly metal and partly polymer). When protruding tab  148  is received in recess  220 , protruding tab  148  and recess  220  together form a “beavertail lock” at or in beavertail portion  248  of grip frame  200 , thereby snugly securing the back end of trigger control unit  100  to grip frame  200 . 
     Referring to  FIG. 9 ˜ FIG. 11 , under a proposed design, locking block  150  may be configured with a pair of longer slide rails  150 C and  150 D, which are longer than  150 A and  150 B, respectively, described above and shown in  FIG. 1 ˜ FIG. 6 . Slide rails  150 C and  150 D may extend forward and protrude from a front side of support frame  140  (even further than slide rails  150 A and  150 B) with respect to the trigger  110 , trigger pin  190  and firearm  50 . When trigger control unit  100  is installed between grip frame  200  and the slide assembly  300 , slide assembly  300  may be movable forwardly and rearwardly with respect to grip frame  200  on the slide rails  150 C and  150 D. Under a proposed design, a flat wall  152 C may extend downward from slide rail  150 C with respect to grip frame  200  and, similarly, a flat wall  152 D may extend downward from slide rail  150 D with respect to grip frame  200 . Moreover, each of flat wall  152 C and flat wall  152 D may be configured with a through hole  152  for receiving locking block pin  192 . Accordingly, when trigger control unit  100  is received, mounted, seated or otherwise installed in a hollow of grip frame  200 , trigger control unit  100  may be fixed or otherwise secured to grip frame by locking block pin  192  (by traversing through holes on grip frame  200  and through holes  152  on flat wall  152 C and flat wall  152 D), trigger pin  190 , and beavertail lock formed by protruding tab  148  and recess  220  as described above. That is, when trigger control unit  100  is secured to grip frame  200 , locking block pin  192  is forward of trigger pin  190  (e.g., compared to trigger pin  1909 , locking block pin  192  is closer to a muzzle of firearm  50  and farther away from the back side of grip frame  200 ). Advantageously, with an opening or cutout on and along centerline  210  of the back side of grip frame  200 , identification marking  60  (e.g., serial number) of firearm  50  displayed on trigger mechanism housing  120  may coincide with centerline  210  as well as the opening/cutout and, therefore, may be visible to a user through the opening or cutout. 
     Each of  FIG. 12 ,  FIG. 13  and  FIG. 14  illustrates a respective view of some of the components of firearm  50  in accordance with a proposed design of the present disclosure. Referring to  FIG. 8  and  FIG. 12 ˜ FIG. 14 , grip frame  200  may have a beavertail portion  248  at the back end thereof. That is, beavertail portion  248  may protrude rearward (e.g., toward a user when firearm  50  is held by the user). Under a proposed design, beavertail portion  248  may be configured with an indentation or recess  220  which may be configured, sized or otherwise dimensioned to receive a protruding tab  148  of trigger control unit  100 . 
     Under a proposed design, protruding tab  148  may be formed by a rearward protrusion of trigger mechanism housing  120 , which may be made of a metal. Under another proposed design, protruding tab  148  may be formed by a rearward protrusion of support frame  140 , which may be made of polymer. Under yet another proposed design, protruding tab  148  may be partially formed by a rearward protrusion of trigger mechanism housing  120  and partially formed by a rearward protrusion of support frame  140 . That is, in this design, protruding tab  148  may be a composite of metal and polymer (e.g., partly metal and partly polymer). When protruding tab  148  is received in recess  220 , protruding tab  148  and recess  220  together form a “beavertail lock” at or in beavertail portion  248  of grip frame  200 , thereby snugly securing the back end of trigger control unit  100  to grip frame  200 . 
     Referring to  FIG. 12 ˜ FIG. 14 , under a proposed design, locking block  150  may be configured with a pair of longer slide rails  150 C and  150 D, which are longer than  150 A and  150 B, respectively, described above and shown in  FIG. 1 ˜ FIG. 6 . Slide rails  150 C and  150 D may extend forward and protrude from a front side of support frame  140  (even further than slide rails  150 A and  150 B) with respect to firearm  50 . When trigger control unit  100  is installed between grip frame  200  and the slide assembly  300 , slide assembly  300  may be movable forwardly and rearwardly with respect to grip frame  200  on the slide rails  150 C and  150 D. Under a proposed design, a flat wall  152 C may extend downward from slide rail  150 C with respect to grip frame  200  and, similarly, a flat wall  152 D may extend downward from slide rail  150 D with respect to grip frame  200 . Moreover, each of flat wall  152 C and flat wall  152 D may be configured with a through hole  152  for receiving locking block pin  192 . Accordingly, when trigger control unit  100  is received, mounted, seated or otherwise installed in a hollow of grip frame  200 , trigger control unit  100  may be fixed or otherwise secured to grip frame by locking block pin  192  (by traversing through holes on grip frame  200  and through holes  152  on flat wall  152 C and flat wall  152 D) and beavertail lock formed by protruding tab  148  and recess  220  as described above. That is, when trigger control unit  100  is secured to grip frame  200 , locking block pin  192  is forward of trigger pin  190  (e.g., compared to trigger pin  1909 , locking block pin  192  is closer to a muzzle of firearm  50  and farther away from the back side of grip frame  200 ). Advantageously, with an opening or cutout on and along centerline  210  of the back side of grip frame  200 , identification marking  60  (e.g., serial number) of firearm  50  displayed on trigger mechanism housing  120  may coincide with centerline  210  as well as the opening/cutout and, therefore, may be visible to a user through the opening or cutout. 
     As can be seen, one major difference between the proposed design shown in  FIGS. 9 ˜ 11  and the proposed design shown in  FIGS. 12 ˜ 14  is that, in the proposed design shown in  FIGS. 9 ˜ 11  trigger control unit  100  is secured to grip frame by three components, namely: locking block pin  192 , trigger pin  120  and the “beavertail lock” formed by protruding tab  148  and recess  220 . In contrast, in the proposed design shown in  FIGS. 12 ˜ 14  trigger control unit  100  is secured to grip frame by two components, namely: locking block pin  192  and the “beavertail lock” formed by protruding tab  148  and recess  220 . 
     Feature Highlight 
     In view of the above, select features of various implementations in accordance with the present disclosure are highlighted below. 
     In one aspect, an apparatus (e.g., a semi-automatic or full-automatic firearm such as firearm  50 ) may include a trigger control unit configured to be removably installed on a grip frame of a firearm. The trigger control unit may include a locking block and a locking block pin. The trigger control unit may have a protruding tab protruding rearward with respect to the firearm. The locking block may include a pair of slide rails extending forward with respect to the firearm, with each slide rail of the pair of slide rails having a flat wall extending downward with respect to the grip frame when the trigger control unit is installed on the grip frame. Accordingly, the trigger control unit may be secured to the grip frame by: (1) the protruding tab received in a recess on an interior wall of a beavertail portion of the grip frame; and (2) the locking block pin traversing through a through hole on the flat wall extending from each slide rail of the pair of slide rails such that removal of the trigger control unit from the grip frame requires removal of the locking block pin. 
     In some implementations, the trigger control unit may also include a trigger mechanism housing configured to be removably received in the grip frame of the firearm. When the trigger control unit is installed between the grip frame and a slide assembly of the firearm, the slide assembly may be movable forwardly and rearwardly with respect to the grip frame on the slide rails. 
     In some implementations, an identification marking of the firearm displayed on the trigger mechanism housing may coincide with a centerline of a back side of the grip frame. 
     In some implementations, the trigger control unit may further include a trigger pin, a trigger pivotable around the trigger pin when pulled, a trigger bar coupled between the trigger and the trigger mechanism housing, and a support frame having a first distal end and a second distal end opposite the first distal end such that the first distal end faces a front side of the grip frame and the second distal end faces the back side of the grip frame when the trigger control unit is installed on the grip frame. 
     In some implementations, the trigger control unit may be secured to the grip frame at least by the protruding tab, the locking block pin and the trigger pin such that removal of the trigger control unit from the grip frame requires removal of the locking block pin and the trigger pin. Additionally, responsive to the trigger being pulled by the user when the trigger control unit is installed between the grip frame and the slide assembly, the trigger bar may cause a sear in the trigger mechanism housing to lower relative to the slide assembly such that the firing pin lug is released. Moreover, the trigger may be pivotably coupled to the first distal end of the support frame with the trigger pin traversing through the trigger and the first distal end of the support frame. Furthermore, the trigger mechanism housing may be coupled to the second distal end of the support frame. 
     In some implementations, the support frame may be made of a polymeric material, metal or a composite of metal and polymer. 
     In some implementations, the trigger mechanism housing may be configured with a left indentation on a left side thereof and a right indentation on a right side thereof. Additionally, the support frame may be configured with a left protrusion on a left inner surface near the second distal end and a right protrusion on a right inner surface near the second distal end. Moreover, the support frame may be coupled to the trigger mechanism housing by the left protrusion received in the left indentation and the right protrusion received in the right indentation. 
     In some implementations, the protruding tab may be formed by either or both of a portion of the support frame and a portion of the trigger mechanism housing. 
     In some implementations, the trigger mechanism housing may be configured to be removably received in each of a plurality of grip frames and installed between each of the plurality of grip frames and each of a plurality of slide assemblies such that: (a) at least two of the plurality of grip frames have different sizes, different colors, or different sizes and colors, or (b) at least two of the plurality of slide assemblies have different sizes, different colors, different calibers, or any combination thereof. 
     In some implementations, the apparatus may also include the grip frame. The grip frame may have an opening on and along the centerline of the back side thereof and aligned with the identification marking of the firearm when the trigger mechanism housing is received in the grip frame such that the identification marking is visible through the opening. In some implementations, the apparatus may further include the slide assembly containing a striker-firing mechanism and longitudinally movable on the grip frame when the slide assembly is installed on the grip frame with the trigger mechanism housing installed between the slide assembly and the grip frame. 
     In another aspect, an apparatus (e.g., a semi-automatic or full-automatic firearm such as firearm  50 ) may include a trigger control unit configured to be removably received in a grip frame of a firearm and installed between the grip frame and a slide assembly of the firearm such that, when activated, the trigger control unit causes firing of one or more rounds of ammunition. The trigger control unit may include a trigger mechanism housing, a trigger pin, a trigger pivotable around the trigger pin when pulled, a trigger bar coupled between the trigger and the trigger mechanism housing, a locking block, a locking block pin, and a support frame having a first distal end and a second distal end opposite the first distal end such that the first distal end faces a front side of the grip frame and the second distal end faces a back side of the grip frame when the trigger control unit is installed on the grip frame. The locking block may include a pair of slide rails extending forward with respect to the trigger and the firearm, with each slide rail of the pair of slide rails having a flat wall extending downward with respect to the grip frame when the trigger control unit is installed on the grip frame. Accordingly, the trigger control unit may be secured to the grip frame by at least the locking block pin such that removal of the trigger control unit from the grip frame requires removal of the locking block pin. 
     In some implementations, an identification marking of the firearm may be displayed on the trigger mechanism housing and, when the trigger mechanism housing is received in the grip frame, may coincide with a centerline of a back side of the grip frame. Accordingly, when the trigger mechanism housing is received in the grip frame, the identification marking of the firearm may be visible through an opening on the back side of the grip frame. 
     In some implementations, when the trigger control unit is installed between the grip frame and the slide assembly, the slide assembly may be movable forwardly and rearwardly with respect to the grip frame on the slide rails. Additionally, the trigger control unit may be secured to the grip frame at least by the locking block pin and the trigger pin such that removal of the trigger control unit from the grip frame requires removal of the locking block pin and the trigger pin. 
     In some implementations, responsive to the trigger being pulled by the user when the trigger control unit is installed between the grip frame and the slide assembly, the trigger bar may cause a sear in the trigger mechanism housing to lower relative to the slide assembly such that the firing pin lug is released. Additionally, the trigger may be pivotably coupled to the first distal end of the support frame with the trigger pin traversing through the trigger and the first distal end of the support frame. Moreover, the trigger mechanism housing may be coupled to the second distal end of the support frame. 
     In some implementations, the trigger control unit may have a protruding tab protruding rearward with respect to the firearm and configured to be received in a recess on an interior wall of a beavertail portion of the grip frame. Accordingly, the trigger control unit may be secured to the grip frame at least by: (1) the protruding tab received in the recess on the interior wall of the beavertail portion of the grip frame; and (2) the locking block pin traversing through a through hole on flat wall extending from each slide rail of the pair of slide rails such that removal of the trigger control unit from the grip frame requires removal of the locking block pin. 
     In some implementations, the protruding tab may be formed by either or both of a portion of the support frame and a portion of the trigger mechanism housing. 
     In some implementations, the trigger mechanism housing may be configured to be removably received in each of a plurality of grip frames and installed between each of the plurality of grip frames and each of a plurality of slide assemblies such that: (a) at least two of the plurality of grip frames have different sizes, different colors, or different sizes and colors, or (b) at least two of the plurality of slide assemblies have different sizes, different colors, different calibers, or any combination thereof. 
     In some implementations, the apparatus may also include the grip frame. The grip frame may have an opening on the back side thereof and aligned with the identification marking of the firearm when the trigger mechanism housing is received in the grip frame such that the identification marking is visible through the opening. In some implementations, the apparatus may further include the slide assembly containing a striker-firing mechanism and longitudinally movable on the grip frame when the slide assembly is installed on the grip frame with the trigger mechanism housing installed between the slide assembly and the grip frame. 
     In yet another aspect, an apparatus (e.g., a semi-automatic or full-automatic firearm such as firearm  50 ) may include a trigger mechanism housing configured to be removably received in a grip frame of a firearm such that, when received in the grip frame, a serial number of the firearm displayed on the trigger mechanism housing may coincide with a centerline of a back side of the grip frame. 
     In some implementations, when the trigger mechanism housing is received in the grip frame, the serial number of the firearm may be visible through an opening on the back side of the grip frame. As the identification marking of the firearm is displayed on the trigger mechanism housing, under current United States laws and regulations, the trigger mechanism housing itself may be considered as a firearm. 
     Additional Notes 
     The herein-described subject matter sometimes illustrates different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are merely examples, and that in fact many other architectures can be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as “associated with” each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being “operably connected”, or “operably coupled”, to each other to achieve the desired functionality, and any two components capable of being so associated can also be viewed as being “operably couplable”, to each other to achieve the desired functionality. Specific examples of operably couplable include but are not limited to physically mateable and/or physically interacting components and/or wirelessly interactable and/or wirelessly interacting components and/or logically interacting and/or logically interactable components. 
     Further, with respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. 
     Moreover, it will be understood by those skilled in the art that, in general, terms used herein, and especially in the appended claims, e.g., bodies of the appended claims, are generally intended as “open” terms, e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc. It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to implementations containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an,” e.g., “a” and/or “an” should be interpreted to mean “at least one” or “one or more;” the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should be interpreted to mean at least the recited number, e.g., the bare recitation of “two recitations,” without other modifiers, means at least two recitations, or two or more recitations. Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention, e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc. In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention, e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc. It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.” 
     From the foregoing, it will be appreciated that various implementations of the present disclosure have been described herein for purposes of illustration, and that various modifications may be made without departing from the scope and spirit of the present disclosure. Accordingly, the various implementations disclosed herein are not intended to be limiting, with the true scope and spirit being indicated by the following claims.