US20250130003A1

US20250130003A1 - Select fire trigger mechanism for machine guns

Info

Publication number: US20250130003A1
Application number: US18/829,620
Authority: US
Inventors: Matthew R. Steinhauser; Kristopher Lee Paulson
Original assignee: CHD Holdings LLC
Current assignee: CHD Holdings LLC
Priority date: 2023-09-16
Filing date: 2024-09-10
Publication date: 2025-04-24
Also published as: US20250093117A1

Abstract

A trigger mechanism can include a selector operable between safe, automatic and semiautomatic positions; a trigger pivotable between set and pulled positions; a hammer pivotable between fired and cocked positions; a hammer sear rotatable via the selector between a disengaged position and an engaged position with the hammer; and a sear trip connected to the hammer sear and movable between an inactive position and an active position in which a reciprocating bolt carrier can contact the sear trip to disengage the hammer sear from the hammer when the bolt carrier reaches a substantially in-battery position. Holding the trigger in the pulled position when the selector is in the automatic position, the bolt carrier is in the substantially in-battery position, and the hammer is in a cocked position, releases the hammer toward the fired position and transitions control of the hammer from the trigger sear to the hammer sear.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS

This non-provisional patent application claims priority to U.S. Provisional Patent Application Ser. No. 63/538,803, filed Sep. 16, 2023 and titled “LIGHT MACHINE GUN,” the entire disclosure of which is hereby incorporated by reference.
A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the reproduction of the patent document or the patent disclosure, as it appears in the U.S. Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

REFERENCE TO SEQUENCE LISTING OR COMPUTER PROGRAM LISTING APPENDIX

Not Applicable.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of firearms, and more particularly, to trigger mechanisms for machine guns.
A machine gun is a fully automatic firearm designed for sustained direct fire. Machine guns tend to function similarly in some ways to traditional firearms, and different in others. The differences are generally designed to increase longevity of the weapon at the expense of weight. For example, machine guns typically use “open bolt” operating systems to help cooling and prevent unintended firing from cookoff. A firearm is said to fire from an “open bolt” if, when ready to file, the bolt is held to the rear of the receiver, with no round in the chamber. When the trigger is pulled, the bolt travels forward, feeds a cartridge into the chamber, and fires that cartridge in the same movement. The “cookoff” phenomenon occurs when the heat in the barrel of the firearm is high enough to fire a cartridge without the firing pin first striking the cartridge primer. Although the open bolt operating system is a workable solution for many applications, it comes at a cost. Specifically, when the operator aims an open bolt weapon and pulls the trigger to fire, the entire bolt mass must be driven forward before the weapon fires. This force generated between pulling the trigger and firing the weapon acts to drive open bolt weapons off target, reducing accuracy.
Additionally, traditional machine guns do not typically offer the ability to switch between open bolt automatic and closed bolt semiautomatic firing modes. A firearm which is said to fire from a “closed bolt” is one where, when ready to fire, a round is in the chamber and the bolt is forward in battery. When the trigger is pulled, a firing pin or striker fires the round, the action is cycled by the energy of the shot, sending rearward the bolt, which extracts and ejects the empty cartridge case before moving forward again to feed a new cartridge into the chamber and make the weapon ready for the next shot. However, advancements in cartridges, links, and machining have yielded new light machine gun platforms that are capable of greater single shot accuracy and accuracy at greater distance, thus driving demand for machine guns capable of making single well-placed shots in a closed bolt semiautomatic firing mode. Moreover, recent military specifications for machine guns require a select fire feature on some open-bolt weapon systems. Accordingly, what is needed are improvements in trigger mechanisms for machine guns.

BRIEF SUMMARY

This Brief Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. Features of the presently disclosed invention overcome or minimize some or all of the identified deficiencies of the prior art, as will become evident to those of ordinary skill in the art after a study of the information presented in this document.
It is an object of the present invention to provide a dual mode firing mechanism that allows the operator to seamlessly go from closed bolt to open bolt fire. It is a further object of the present invention to provide a select fire trigger mechanism for a machine gun that permits initiation of automatic fire from either of a closed or open bolt position. This changing of firing modes is accomplished simply by moving the selector lever to different positions to simultaneously (i) engage or disengage a carrier sear that acts to retain the bolt carrier rearward when engaged, (ii) engage or disengage a disconnector, and (iii) change control of the hammer from a trigger sear to a hammer sear via a sear trip that is acted upon by the bolt carrier. The nature of these interactions is reconfigurable in terms of the correlation between selector position and firing mode so as to make the resulting weapon system customizable to the needs of a given operator or application. Additionally, the present trigger mechanism is advantageously designed to fire cartridges using a hammer, which gives the weapon a refined trigger pull in semiautomatic mode and for the first round of fully automatic fire from the closed bolt. It is yet another object of the present invention to provide a select fire trigger mechanism for a machine gun that permits charging when the weapon is in a safe condition.
Accordingly, in one embodiment, the invention provides a trigger mechanism for a firearm having a bolt carrier that reciprocates and pivotally displaces a hammer when cycled between a closed in-battery position and an open position, the trigger mechanism comprising: a selector operable between a safe position, a semiautomatic position, and an automatic position; a trigger pivotable between a set position and a pulled position; a disconnector pivotably connected to the trigger and pivotable via the selector between a working position in which a part of the disconnector is in an arcuate path of the hammer when the selector is in the semiautomatic position, and a retracted position in which the part of the disconnector is out of the path of the hammer when the selector is in the automatic position; a carrier sear pivotable between a disengaged position in which the carrier sear is spaced from the bolt carrier and an engaged position in which the carrier sear is arranged to engage the bolt carrier and prevent the bolt carrier from moving toward the closed in-battery position, the carrier sear biased toward the engaged position when the selector is in the automatic position and the trigger is not in the pulled position; and a sear arm pivotably connected to the carrier sear and movable to pivot the carrier sear toward the disengaged position by pulling the trigger when the selector is in the automatic position.
In another embodiment, the invention provides a trigger mechanism for a firearm having a bolt carrier that reciprocates and pivotally displaces a hammer when cycled, the trigger mechanism comprising: a selector operable between a safe position, an automatic position, and a semiautomatic position; a trigger defining a trigger sear and pivotable between a set position and a pulled position; a hammer defining a semiautomatic sear surface and an automatic sear surface, the hammer pivotable between a fired position and at least one cocked position, the hammer biased toward the fired position; a hammer sear rotatable via the selector between a disengaged position in which the hammer sear is arranged to not engage the hammer and an engaged position in which the hammer sear is arranged to engage the hammer when the hammer is in an automatic cocked position, wherein the hammer sear is biased toward the engaged position when the selector is in the automatic position and toward the disengaged position when the selector is not in the automatic position; and a sear trip connected to the hammer sear and movable via the hammer sear between an inactive position in which a part of the sear trip is arranged so as not to be contacted by the bolt carrier during cycling thereof, and an active position in which the part of the sear trip is arranged to be contacted by the bolt carrier when the bolt carrier reaches a substantially in-battery position during cycling thereof, wherein the sear trip is biased toward the active position when the selector is in the automatic position and biased toward the inactive position when the selector is not in the automatic position, and wherein contact by the bolt carrier with the part of the sear trip moves the sear trip against the bias to rotate the hammer sear, disengage the hammer sear from the hammer, and release the hammer toward the fired position.
Numerous other objects, advantages and features of the present disclosure will be readily apparent to those of skill in the art upon a review of the following drawings and description of exemplary embodiments.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various drawings unless otherwise specified. In the drawings, not all reference numbers are included in each drawing, for the sake of clarity.

FIG. 1 is an elevated front left side perspective view of a novel hammer-fired belt fed machine gun equipped with a novel select fire trigger mechanism constructed in accordance with an embodiment of the present invention. The machine gun is depicted in-battery in a non-firing, safe mode with the selector in the safe position, the hammer in the semiautomatic cocked position, and the trigger in the set position.

FIG. 2 is a partially exploded left side perspective view of the fire control assembly of the machine gun of FIG. 1 .

FIG. 3 is an elevated rear left side perspective view of the trigger housing portion of the trigger mechanism of FIG. 2 shown in isolation.

FIG. 4A is an elevated exploded rear left side perspective view of the trigger mechanism of FIG. 1 . The trigger housing is omitted for clarity.

FIG. 4B is an elevated exploded front right side perspective view of the trigger mechanism of FIG. 1 . The trigger housing is omitted for clarity.

FIG. 5A is a first perspective view of the selector of FIG. 1 . A selector lever is mounted on the right side of the selector barrel for clarity.

FIG. 5B is another perspective view of the selector of FIG. 5A.

FIG. 5C is still another perspective view of the selector of FIG. 5A.

FIG. 5D is a sectional view taken along line D of FIG. 5A.

FIG. 5E is a sectional view taken along line E of FIG. 5A.

FIG. 5F is a sectional view taken along line F of FIG. 5A.

FIG. 6A is a left side elevational view of the trigger mechanism and bolt carrier of the machine gun of FIG. 1 .

FIG. 6B is a magnified detail view of FIG. 6A at location B with the trigger housing and hammer spring omitted for clarity.

FIG. 6C is a magnified detail view of FIG. 6B at location C.

FIG. 7 is an elevated front left side perspective view of the trigger and selector of FIG. 6B in isolation. The left side selector lever is omitted for clarity.

FIG. 8A is an elevated rear left perspective view of the objects of FIG. 6B with the hammer spring guide rod omitted so as to more clearly show the hammer sear being maintained in the disengaged position by the selector barrel, and the sear arm resting in the ready position on the trigger cross member.

FIG. 8B is a magnified left side elevational view of the trigger, selector barrel, sear arm, and carrier sear of FIG. 8A with the other trigger mechanism components omitted for clarity so as to more clearly show the sear arm in the ready position on the selector barrel and the carrier sear upward in the engaged position.

FIG. 9A is a left side elevational view of the trigger mechanism and bolt carrier of the machine gun of FIG. 1 in a semiautomatic firing mode with the selector in the semiautomatic position, the bolt carrier in the in-battery position, the hammer in the semiautomatic cocked position, and the trigger in the set position.

FIG. 9B is a magnified detail view of FIG. 9A at location B with the trigger housing, hammer spring guide rod, and hammer spring omitted for clarity.

FIG. 9C is magnified left side elevational view of the trigger, selector barrel, sear arm, and carrier sear of FIG. 9B. The trigger is shown in transparency and the other trigger mechanism components are omitted for clarity.

FIG. 10 is an elevated rear left side perspective view of the trigger and selector of FIG. 9B in isolation. The right side selector lever is omitted.

FIG. 11 is an elevated rear left side perspective view of the objects of FIG. 9B.

FIG. 12 is a right side elevational view of the objects of FIG. 11 in a fired condition just after the trigger is pulled.

FIG. 13 is a right side elevational view of the objects of FIG. 12 depicting the bolt carrier reciprocating rearwardly to reset the trigger mechanism.

FIG. 14 is a left side elevational view of the objects of FIG. 13 depicting the bolt carrier reciprocating further rearward so as to more clearly show the carrier sear being held in the disengaged position below the sear notch in the bolt carrier.

FIG. 15 is a right side elevational view of the objects of FIG. 14 depicting the bolt carrier reciprocated fully rearward in the open position with the hammer on the disconnector ready to reset when the trigger is released and the bolt carrier reaches the in-battery position.

FIG. 16 is a right side elevational view of the objects of FIG. 15 depicting the bolt carrier having reciprocated almost completely back into the in-battery position with the hammer held in place by the disconnector.

FIG. 17 is a right side elevational view of the objects of FIG. 16 depicting the bolt carrier in battery with the trigger released into the set position and the hammer transitioned from the disconnector to the trigger sear in the semiautomatic cocked position ready to fire again.

FIG. 18A is a left side elevational view of the trigger mechanism and bolt carrier of the machine gun of FIG. 1 in an automatic firing mode with the selector in the automatic position.

FIG. 18B another left side elevational view of the objects of FIG. 18A with the trigger housing and hammer spring omitted for clarity.

FIG. 18C is a magnified detail view of FIG. 18B at location C.

FIG. 18D is magnified left side elevational view of the trigger, selector barrel, sear arm, and carrier sear of FIG. 18B with the other trigger mechanism components omitted for clarity.

FIG. 19 is a left side elevational view of the objects of FIG. 18B in a fired condition just after the trigger is pulled.

FIG. 20 is an elevated right side perspective view of the objects of FIG. 19 with the hammer spring guide rod and right side selector lever omitted for clarity.

FIG. 21 is a right side elevational view of the objects of FIG. 20 depicting the trigger in the pulled position with the bolt carrier traveling rearward and pivotally displacing the hammer.

FIG. 22 is a right side elevational view of the objects of FIG. 21 depicting the trigger in the pulled position with the bolt carrier in a rearward position and the hammer sear engaging the hammer in the automatic cocked position.

FIG. 23A is a left side elevational view of the objects of FIG. 22 depicting the bolt carrier approaching the in-battery position.

FIG. 23B is a left side elevational view of the objects of FIG. 23A with the trigger housing shown for clarity.

FIG. 24 is an enlarged right side view of the selector barrel, hammer sear, sear trip, and hammer of FIG. 23A illustrating via arrows the mechanical cascade caused by the bolt carrier contacting the sear trip and moving the sear trip against the sear trip return spring to the tripped position.

FIG. 25A is a left side elevational view of the objects of FIG. 23B depicting the bolt carrier in the in-battery position, the sear trip in the tripped position, and the hammer in the fired position.

FIG. 25B is a left side elevational view of the objects of FIG. 25A with the trigger housing omitted for clarity.

FIG. 26 is a right side elevational view of the objects of FIG. 25B depicting the bolt carrier in a rearward position with the hammer reset on the hammer sear while the trigger is still in the pulled position.

FIG. 27 is a left side elevational view of the objects of FIG. 26 depicting the hammer in the automatic cocked position and the bolt carrier locked in the open position upon cessation of automatic fire.

DETAILED DESCRIPTION

The details of one or more embodiments of the present invention are set forth in this document. Modifications to embodiments described in this document, and other embodiments, will be evident to those of ordinary skill in the art after a study of the information provided herein. The information provided in this document, and particularly the specific details of the described exemplary embodiment(s), is provided primarily for clearness of understanding and no unnecessary limitations are to be understood therefrom. In case of conflict, the specification of this document, including definitions, will control.
While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts that are embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and do not delimit the scope of the invention. Those of ordinary skill in the art will recognize numerous equivalents to the specific apparatus and methods described herein. Such equivalents are considered to be within the scope of this invention and are covered by the claims.
While the terms used herein are believed to be well understood by one of ordinary skill in the art, a number of terms are defined below to facilitate the understanding of the embodiments described herein. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the subject matter disclosed herein belongs. The terms defined herein have meanings as commonly understood by a person of ordinary skill in the areas relevant to the present invention. Terms such as “a,” “an,” and “the” are not intended to refer to only a singular entity, but rather include the general class of which a specific example may be used for illustration. The terminology herein is used to describe specific embodiments of the invention, but their usage does not delimit the invention, except as set forth in the claims.
As described herein, an “upright” position is considered to be the position of apparatus components while in proper operation or in a natural resting position as described and shown herein, for example, in FIG. 1 . “Vertical,” “horizontal,” “above,” “below,” “side,” “top,” “bottom,” “upper,” “lower,” and other orientation terms are described with respect to this upright position during operation, unless otherwise specified, and are used to provide an orientation of embodiments of the invention to allow for proper description of example embodiments. A person of skill in the art will recognize, however, that the apparatus can assume different orientations when in use.
As used herein, the terms “front” and “forward” means in a direction extending toward the muzzle of the firearm. In some cases, the term “forward” can also mean forward beyond the muzzle of the firearm. The terms “aft” and “rear” means in a direction extending away from the muzzle of the firearm toward a rear end of a firearm. In some cases, the term “rearward” can also mean rearward beyond the rear end of the firearm.
The term “when” is used to specify orientation for relative positions of components, not as a temporal limitation of the claims or apparatus described and claimed herein unless otherwise specified.
The terms “above”, “below”, “over”, and “under” mean “having an elevation or vertical height greater or lesser than” and are not intended to imply that one object or component is directly over or under another object or component.
The phrase “in one embodiment,” as used herein does not necessarily refer to the same embodiment, although it may. Conditional language used herein, such as, among others, “can,” “might,” “may,” “e.g.,” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or states. Thus, such conditional language is not generally intended to imply that features, elements and/or states are in any way required for one or more embodiments.
All measurements should be understood as being modified by the term “about” regardless of whether the word “about” precedes a given measurement.
The terms “significantly”, “substantially”, “approximately”, “about”, “relatively,” or other such similar terms that may be used throughout this disclosure, including the claims, are used to describe and account for small fluctuations, such as due to variations in manufacturing or processing from a reference or parameter. Such small fluctuations include a zero fluctuation from the reference or parameter as well. For example, they can refer to less than or equal to ±10%, such as less than or equal to ±5%, such as less than or equal to ±2%, such as less than or equal to ±1%, such as less than or equal to ±0.5%, such as less than or equal to ±0.2%, such as less than or equal to ±0.1%, such as less than or equal to ±0.05%. In some cases, the term “substantially” as used herein means what is considered normal or possible within the limits of applicable industry-accepted manufacturing practices and tolerances.
All references to singular characteristics or limitations of the present disclosure shall include the corresponding plural characteristic(s) or limitation(s) and vice versa, unless otherwise specified or clearly implied to the contrary by the context in which the reference is made.
All combinations of method or process steps as used herein can be performed in any order, unless otherwise specified or clearly implied to the contrary by the context in which the referenced combination is made.
The methods and devices disclosed herein, including components thereof, can comprise, consist of, or consist essentially of the essential elements and limitations of the embodiments described herein, as well as any additional or optional components or limitations described herein or otherwise useful.
Referring now generally to FIGS. 1-5C, there is depicted a novel firearm in the form of a hammer-fired belt fed machine gun 2 containing a novel select fire trigger mechanism 10 constructed in accordance with an embodiment of the present invention. The machine gun 2 defines a bore axis 5 and includes a fire control housing 4 in which the trigger mechanism 10 is housed. The trigger mechanism 10 includes a trigger housing 15 defining an interior pocket 16 in which most of the operational components of the trigger mechanism 10 are housed. The trigger housing 15, and thus the trigger mechanism 10, is secured in the fire control housing 4 by a pistol grip 6 and a fastener 8. Specifically, the trigger housing 15 defines a tang 11 that extends through the fire control housing 4 and is received in the pistol grip 6, which abuts an underside of the fire control housing 4. A fastener 8 extending through the pistol grip 6 and is threadingly engaged with a threaded socket 13 in the tang 11 that creates a clamping force which holds the trigger mechanism 10 in the fire control housing 4. The machine gun 2 also includes a bolt carrier 12 containing a conventional firing pin (not shown). The bolt carrier 12 reciprocates along the axis 5 to pivotally displace the hammer when the bolt carrier 12 is cycled between a closed or in-battery position and an open position, as will be familiar to artisans of ordinary skill in the art.
As best shown in FIG. 3 , the trigger housing 15 defines a plurality of transversely aligned pairs of holes 18 through which various pins are receivable to pivotally and rotatably mount certain components of the trigger mechanism to the trigger housing 15, as described in more detail below. As such, in the depicted embodiment, the assembled trigger mechanism 10 can form a cassette type trigger module that can be quickly and easily installed and removed from the fire control housing 4. In other embodiments (not shown), the trigger housing 15 can be omitted and the various operational components of the trigger mechanism can be mounted directly to the fire control housing 4 or a receiver sidewall. The trigger housing 15 defines a track 85 formed on an exterior of the trigger housing 15. In some embodiments not shown, the track 85 can be defined on an interior surface of the trigger housing 15. The trigger housing 15 also defines a spring stud stop 104 and a stud guide 106 in the track 85.
As best shown in FIGS. 4A-4B, the trigger mechanism 10 includes a hammer 14, a trigger 20, a disconnector 22, a safety selector 24, a sear arm 26, a carrier sear 28, a hammer sear 30, a sear trip 32, a hammer spring guide rod 34, a spring hook 36, a hammer spring perch 38, a safety selector plunger 102 and various pins and springs. The safety selector 24 is designed to be ambidextrously operable and includes a selector barrel 40 and a pair of selector levers 42. The selector levers 42 are removably attached to each end of the selector barrel 40 by threaded fasteners 44. The selector barrel 40 is rotatably mounted in the trigger housing 15. The selector barrel 40 extends through a pair of transversely aligned holes 18 in the trigger housing 15 as well as a corresponding pair of transverse aligned holes 18 in the fire control housing 4. The selector levers 42 secured to the ends of the selector barrel 40 at opposing exterior surfaces of the fire control housing 4 further aid in securing the trigger mechanism 10 to the fire control housing 4. The safety selector 24 is rotatable between a safe position, a semiautomatic position, and an automatic position.
The trigger 20 and disconnector 22 are pivotably mounted to the trigger housing 15 by a transverse trigger pin 46 received in another one of the pairs of transversely aligned holes 18. The hammer 14 is pivotably mounted to the trigger housing 15 by a transverse hammer pin 48 received in yet another one of the pairs of transversely aligned holes 18. The hammer 14 pivots along an arcuate path. The hammer 14 is biased toward a fired position (see, e.g., FIG. 12 ) by a hammer spring 33. The hammer spring 33 is seated on the hammer spring guide rod 34. A forward end of the hammer spring guide rod 34 is received in the spring hook 36. The spring hook 36 is mounted to the hammer 14 by a spring boss 35. The spring boss 35 extends through the hammer 14. The spring boss 35 is proximate the hammer pin 48. A rear end of the hammer spring guide rod 34 is received in the spring perch 38. The spring perch 38 is mounted to the carrier sear 28 and trigger housing 15 by a trip pin 52.
The hammer sear 30 is rotatably mounted to the trigger housing 15 by a trip pin 50. The carrier sear 28 is rotatably mounted to the trigger housing 15 by another trip pin 52. Each trip pin 50, 52 includes an end that defines a flat surface 54. The flat surface 54 aligns with an exterior surface 53 of the trigger housing 15, which rests against a protruding ledge (not shown) on an interior surface of the fire control housing 4 when assembled. This arrangement captures the trip pins 50, 52 against the fire control housing 4 and ensures they do not walk out of their respective transversely aligned holes 18 during firing of the machine gun 10.
The trigger 20 includes a trigger body 54 defining a trigger sear 55 and a slot 56 in which the disconnector 22 is received. The disconnector 22 pivots in the slot 56 of the trigger 20. A cross member 58 in the form of a transverse coiled spring pin 58 extends across the slot 56 at an opposite end of the trigger body 54 from the trigger sear 55. The trigger sear 55 engages a corresponding trigger sear notch 57 on the hammer 14 when the hammer is in the semiautomatic cocked position (see FIG. 6B).
The sear arm 26 is pivotably connected to the carrier sear 28 by a transverse coiled spring pin 60. The sear arm 26 defines a fork 62 and a spur 64. The spur 64 rides on the selector barrel 40. As such, the surface geometry of the selector barrel 40 (e.g., a cam profile) dictates the range of motion and, in some cases, the specific position of, the sear arm 26 and carrier sear 28, as described in more detail below. The fork 62 includes two spaced tines 66. One fork tine 66 is received in the slot 56 of the trigger body 54 with the cross member 58 received in a space 68 between the fork tines 66. In this way, the trigger body 54, sear arm 26, and carrier sear 28 are arranged so that the sear arm 26 is both rotatable and linearly movable yet travel locked on the trigger body 54 when the trigger mechanism 10 is assembled. A compression spring 70 in the trigger housing 15 biases the carrier sear 28 upward toward an engaged position (see, e.g., FIG. 6B) when the selector barrel 40 does not restrict the specific position of the carrier sear 28 to the disengaged position (see, e.g., FIGS. 9B-9C). Put another way, the carrier sear 28 is biased toward the engaged position when the selector 24 is in the safe position. The carrier sear 28 retains the bolt carrier 12 in the open position when the carrier sear 28 engages the bolt carrier 12.
The hammer sear 30 includes a main body 72, a finger 74, a tubular portion 76 through which trip pin 50 extends, a sear block 78 on the main body 72, and a stud 80. The sear block 78 defines a hammer sear surface 82. The hammer sear surface 82 engages a corresponding complimentary automatic sear surface 84 define by a hook 87 on the hammer 14 during automatic fire, as explained in more detail below. The stud 80 protrudes from a side of the main body 72 opposite the tubular portion 76 and the sear block 78. The finger 74 protrudes generally downwardly from the main body 72. The finger 74 rides on the selector barrel 40. As such, the surface geometry of the selector barrel 40 (e.g., another cam profile) dictates the range of motion and, in some cases, the specific position of, the finger 74 and thus the hammer sear 30, as described in more detail below.
The sear trip 32 is an elongated member slidably mounted in the track 85 on the trigger housing 15. The sear trip 32 reciprocates forward and rearward in the track 85. The track 85 constrains the sear trip 32 to longitudinal movement. The sear trip 32 includes a forward end 86, and a rear end 88. The forward end 86 defines an upwardly extending protrusion 90. The protrusion 90 is arranged so as to be contacted by a boss 100 on the bolt carrier 12 when the sear trip 32 is in the active position. In some embodiments, the protrusion 90 can be bent or curved toward the axis 5 so as to be in a path of the boss 100 during bolt carrier 12 reciprocation. The sear trip 32 has a plurality of apertures defined therethrough, including a spring slot 92, a stud hole 94, and a guide slot 96. The spring stud stop 104 is received in the spring slot 92 and the stud guide 106 is received in the guide slot 96 when the sear trip 32 is received in the track 85 on the trigger housing 15. A return spring 93 is received in the spring slot 92 against the spring stud stop 104. The spring 93 pushes against the spring stud stop 104 to bias the sear trip 32 longitudinally rearward along the track 85 toward the active position.
The hammer sear stud 80 is received in the stud hole 94 when the sear trip 32 is received in the track 85 and connected to the hammer sear 30. The hammer sear stud 80 is rotatable in the stud hole 94. In this way, the hammer sear 30 is pivotably connected to the sear trip 32 such that the sear trip 32 is movable via the hammer sear 30 between an inactive position in which the protrusion 90 of the sear trip 32 is arranged so as not to be contacted by the bolt carrier 12 during cycling thereof, and an active position in which the protrusion 90 is arranged to be contacted by the bolt carrier 12 when the bolt carrier 12 reaches a substantially in-battery position. The sear trip 32 is biased toward the active position when the selector 24 is in the automatic position and biased toward the inactive position when the selector 24 is not in the automatic position. Contact by the bolt carrier 12 with the sear trip 32 moves the sear trip 32 against the bias to rotate the hammer sear 30 and thereby disengage the hammer sear 30 from the hammer 14 to release the hammer 14 toward the fired position.
Referring now to FIGS. 5A-5F, the safety selector 24 defines multiple sections (i.e., regions) along the length of the selector barrel 40 having different surface geometries with unique circumferential profiles (i.e., cam profiles) including recesses and cam lobes which dictate the ranges of motion and specific positions of certain other components of the trigger mechanism 10 based on the firing mode of the weapon (e.g., safe firing mode, semiautomatic firing mode, automatic firing mode) set by a user via the safety selector lever 42. For example, in the depicted embodiment, the selector barrel 40 defines three cam profiles or sections 110, 112, and 114 along the circumferential surface of the barrel 40 which dictate the firing mode of the weapon. The selector 24 is depicted in FIG. 5A in the safe position from an elevated position to the rear left side of the selector 24. The first section 110 defines a safety cam lobe 116, a reduced diameter portion 117, a trigger body recess 118. The second section 112 is positioned in the middle of the first section 110. The safety cam lobe 116 and the trigger body recess 118 are spaced across the second section 112 from the reduced diameter portion 117. The second section 112 can define a cam lobe 120 and at least one cutout 122. The third section 114 is spaced from the first and second sections 110, 112. The third section 114 can define a niche 124.
The arrangement of the selector barrel sections 110, 112, 114 around the circumference of the selector barrel 40 are independently variable, meaning that the geometries of each section or region can be rearranged around the barrel 40 relative to one another in order to reorient the position in which the selector levers 42 point to indicate the firing mode of the weapon based on the requirements of a given user group or tactical application. For example, although the embodiment exemplified in the figures depicts the safe position in FIG. 6A as being at approximately 10 o'clock (indicated in the figures by the number “0”), the semiautomatic position in FIG. 9A as being at approximately 3 o'clock (indicated in the figures by the number “1”), and the automatic position in FIG. 18A as being at approximately 7 o'clock (indicated in the figures by the letter “X”), these safety selector positions can be changed to rearrange the position of each firing mode by reorienting the regions around the circumference of the selector barrel 40 where desired.

Safe Mode

Turning to FIGS. 6A-8B, the trigger mechanism 10 is depicted in the safe mode with the safety selector 24 in the safe position. The safe mode is dictated by the safety cam lobe 116 on the first section 110 of the selector barrel 40. As best shown in FIG. 7 , when the safety selector 24 is in the safe position, the safety cam lobe 116 engages a rear end of the trigger body 54 to physically prevent the trigger 20 from being pulled (i.e., pivoted out of the set position) by restricting trigger travel. This prevents the weapon from being fired, but does not prevent the weapon from being charged. The bolt carrier can be moved from the in-battery position to the open position when the selector is in the safe position. The hammer sear 30 is maintained in the disengaged position by virtue of the hammer sear finger 74 riding on the outermost circumferential surface 45 of the selector barrel 40. The sear trip 32 is maintained in the inactive position by virtue of the connection to the hammer sear 30 at the hammer sear stud 80. More specifically, the selector barrel surface 45 rotates the hammer sear 30 to the disengaged position, and the hammer sear 30 in turn biases the sear trip 32 forward to the inactive position, thereby compressing the sear trip return spring 93 in the spring slot 92 of the sear trip 32 against the spring stud stop 104 on the trigger housing 15. As best exemplified in FIG. 6C, the sear trip 32 is in the inactive position when the protrusion 90 at the forward end 86 of the sear trip 32 is spaced from the boss 100 on the bolt carrier 12 so that the protrusion 90 cannot be contacted by the boss 100 when the bolt carrier 12 is in battery.
With the safety selector 24 in the safe position, the carrier sear 28 is in the engaged position and the sear arm 26 is in a ready position. The sear arm 26 is in the ready position when the sear arm 26 is arranged to pivot the carrier sear 28 toward the disengaged position when the trigger 20 is pulled. More specifically, the safety selector 24 being in the safe position permits the compression spring 70 in the trigger housing 15 to bias the carrier sear 28 upward toward an engaged position, and thereby pivot the sear arm 26 to the ready position. The sear arm 26 is in the ready position when the spur 64 is received in the cutout 122 in the second section 112 of the selector barrel 40 and the cross member 58 on the trigger 20 is received in the space 68 between the tines 66 of the sear arm fork 62, as best shown in FIG. 8B. This arrangement enables the sear arm 26 to ride on and move with the cross member 58 when the trigger 20 is pulled and released.

Semiautomatic Firing Mode

Turning next to FIGS. 9A-17 , the trigger mechanism 10 is depicted in the semiautomatic firing mode with the safety selector 24 in the semiautomatic position. As best illustrated in FIG. 9B, when the safety selector 24 is in the semiautomatic position, the hammer 14 is in the semiautomatic cocked position with the trigger 20 in the set position and the disconnector 22 in the working position. The disconnector 22 is biased toward the working position by a spring 23 when the selector 24 is in the semiautomatic position. The hammer sear 30 is maintained in the disengaged position by the selector barrel 40 and the sear trip 32 is maintained in the inactive position by the hammer sear 30, as explained above with respect to the safe firing mode. The hammer sear 30 being maintained in the disengaged position by the selector barrel 40 permits the hammer 14 to freely pivot from the semiautomatic cocked position (FIG. 11 ), to the fired position (FIG. 12 ), and back through reset (FIGS. 13-16 ) to the semiautomatic cocked position again (FIG. 17 ) without the automatic sear surface 84 on the hammer 14 contacting the sear block 78 on the hammer sear body 72. This prevents the hammer 14 from engaging the hammer sear surface 82 on the hammer sear 30 during semiautomatic travel of the hammer 14.
The semiautomatic firing mode is controlled in part by the trigger body recess 118 and the reduced diameter portion 117 in the first section 110 of the selector barrel 40, as well as the cam lobe 120 and cutout 122 in the second section 112. The cutout 122 is opposite the cam lobe 120 around the circumference of the second section 112. When the safety selector 24 is in the semiautomatic position, the safety cam lobe 116 is rotated away from the trigger body 54 so as to allow the trigger 20 to pivot into the trigger body recess 118 and against the reduced diameter portion 117 when the trigger 20 is pulled, as best shown in FIG. 10 . Trigger overtravel is limited by the trigger body recess 118 and reduced diameter portion 117.
As best shown in FIG. 9C when the safety selector 24 is in the semiautomatic position, cam lobe 120 on the second section 112 of the selector barrel 40 contacts the spur 64 of the sear arm 26 and raises or elevates the sear arm 26 into the static position. This in turn pivots the carrier sear 28 to, and maintains the carrier sear 28 in, the disengaged position, as shown in FIG. 9C. The cutout 122 in the second section 112 is shaped and size to receive a rear end of the disconnector 22 when the disconnector 22 pivots to reset the hammer 14 during semiautomatic fire.
As explained in more detail below, in semiautomatic fire mode, the bolt carrier 12, the hammer 14, the trigger 20, and the disconnector 22 of the novel trigger mechanism 10 disclosed herein are designed to function in the same manner as a traditional AR-15 platform semiautomatic trigger, with all of the automatic fire-related components of the trigger mechanism 10 (e.g., the hammer sear 30, sear trip 32, and carrier sear 28) positioned in their respective disengaged and inactive positions via the selector 24. This advantageously reduces the time necessary to train new operators on the platform by increasing operator familiarity with the platform in semiautomatic fire mode.
For example, FIG. 12 depicts the trigger mechanism 10 in semiautomatic fire mode just after the trigger 20 is pulled. The bolt carrier 12 is in the in-battery position, the trigger 20 is in the pulled position, the hammer 14 in the fired position against a rear end of the bolt carrier 12, the sear arm 26 is in the static position, and the carrier sear 28 is in the disengaged position. The hammer sear 30 remains maintained in the disengaged position via the selector barrel 40. The sear trip 32 remains maintained in the inactive position via leverage applied to it by the hammer sear 30 through the hammer sear stud 80. FIG. 13 depicts the bolt carrier reciprocating rearwardly to reset the trigger mechanism 10. The trigger remains in the pulled position, while the hammer 14 is pivoted rearward by the rearwardly moving bolt carrier 12. Notably, the hook 87 defining the automatic sear surface 84 on the hammer 14 is spaced from and does not contact the sear block 78 on the hammer sear body 72 during hammer movement. FIG. 14 shows the bolt carrier 12 continuing to move rearward so as to more clearly show the carrier sear 28 being held in the disengaged position below the sear notch 125 in the bolt carrier 12. The spur 64 on the sear arm 26 riding on the selector barrel 40 in the static position maintains the carrier sear 28 in the disengaged position and thereby prevents the carrier sear 28 from pivoting toward the engaged position to engage the sear notch 125 on the bolt carrier 12 and undesirably hold the bolt carrier 12 in the open position during semiautomatic fire. FIG. 15 shows the bolt carrier 12 reciprocated fully rearward with the hammer 14 on the disconnector 22 ready to reset to the semiautomatic cocked position when the trigger 20 is released and the bolt carrier 12 returns to the in-battery position. FIG. 16 shows the bolt carrier 12 having reciprocated almost completely back into the in-battery position with the hammer 14 held in place by the disconnector 22. FIG. 17 shows the bolt carrier 12 back in battery with the trigger 20 released back the set position and the hammer 14 transitioned from the disconnector 22 to the trigger sear 55 in the semiautomatic cocked position ready to fire again upon another pull of the trigger 20.

Automatic Firing Mode

Turning next to FIGS. 18A-27 , the trigger mechanism 10 is depicted in the automatic firing mode with the safety selector 24 in the automatic position. Notably, when the trigger mechanism 10 is switched to automatic fire mode from either safe mode (see FIGS. 6A-6C) or semiautomatic fire mode (see FIGS. 9A-9C), as is best shown in FIGS. 18A-18D, the first shot fired will be from a “closed bolt” position because the bolt carrier will be in-battery with a round chambered and the hammer will be in the semiautomatic cocked position. This entirely unique feature of the present invention represents a dramatic improvement over available machine gun trigger mechanisms by enabling a user to begin automatic fire with a carefully aimed first shot having a crisp trigger break typical of semiautomatic rifles. Subsequent automatic shots will be from an “open bolt” position as described elsewhere herein. Consequently, pulling and holding the trigger 20 in the pulled position when (i) the selector 24 is in the automatic position, (ii) the bolt carrier 12 is in a substantially in-battery position, and (iii) the hammer 14 is in the semiautomatic cocked position, releases the hammer 14 toward the fired position and transitions control of the hammer 14 from the trigger sear 55 to the hammer sear 30.
Releasing the trigger 20 while the machine gun is in automatic fire mode will cause the bolt carrier 12 to lock rearwardly in the open position, as is typically for open bolt belt fed machine guns, so as to avoid loading a round in a hot chamber and causing cook off. Switching the selector 24 from the automatic position to either the safe position or the semiautomatic position while the carrier sear 28 is in the engaged position holding the bolt carrier 12 in the open position moves the selector barrel 40 to allow the sear arm 26 to pivot the carrier sear 28 from the engaged position to the disengaged position and release the bolt carrier 12 from the open position toward the closed in-battery position. This should be done only after the chamber has cooled sufficiently to negate the risk of one or more rounds cooking off.
As shown in FIGS. 18A-18D, when the safety selector 24 is moved to the automatic position from either the safe position (see FIGS. 6A-6C) or semiautomatic position (see FIGS. 9A-9C), the bolt carrier 12 will be in battery, the hammer 12 will be in the semiautomatic cocked position, and the trigger 20 will be in the set position. Additionally, rotation of the selector 24 to the automatic position causes the cam lobe 120 on the second section 112 of the selector barrel 40 to push the disconnector 22 downward out of the path of the hammer 14 into the retracted position. On the other hand, moving the selector 24 from the automatic position to the semiautomatic position pivots the disconnector 22 from the retracted position to the working position. As such, the safety selector 24 is rotatable to pivot the disconnector 22 between the retracted and working positions.
At the same time the disconnector 22 is pushed to the retracted position, the cutout 122 on the second section 112 of the selector barrel 40 is rotated around under the spur 64 of the sear arm 26. This allows the fork 62 of the sear arm 26 to lower into the ready position (i.e., onto the cross member 58 of the trigger 20) as best shown in FIG. 18D, which in turn pivots the carrier sear 28 to the engaged position until the trigger 20 is pulled. Rotation of the selector 24 to the automatic position also causes the selector barrel 40 to rotate the niche 124 of the third section 114 around to face the finger 74 of the hammer sear 30. The return spring 93 in the sear trip 32 applies a constant rearward biasing force to the sear trip 32, which moves the stud 80 received in the stud hole 94 longitudinally rearward to pivot the hammer sear main body 72 around the trip pin 50 and move the finger 74 into the niche 124. In this way, moving the selector 24 to the automatic position moves the hammer sear 30 to the engaged position. As best shown in FIG. 18C, the resulting rearward movement of the sear trip 32 toward the active position places the sear trip protrusion 90 into contact with the boss 100 on the bolt carrier 12 while the bolt carrier is in battery. The sear trip 32 is now in the tripped position. The sear trip 32 and sear trip protrusion 90 will move slightly further rearward than is depicted in FIG. 18A and into the active position (e.g., ready to be tripped) when the bolt carrier 12 moves longitudinally rearward during reciprocation.
FIGS. 19-20 depicts the trigger mechanism 10 and bolt carrier 12 just after the trigger 20 is pulled when the hammer 14 reaches the fired position. The finger 74 of the hammer sear 30 can be clearly seen riding in the niche 124 on the selector barrel 40 in FIG. 20 . The disconnector 22 remains held out of the arcuate path of the hammer 14 in the retracted position by the cam lobe 120 on the second section 112 of the selector barrel 40. FIG. 21 depicts the bolt carrier 12 traveling rearward and pivotally displacing the hammer 14 while the trigger remains in the pulled position. Rearward pivotal displacement of the hammer 14 by the bolt carrier 12 slides the hook 87 past the sear block 78 by rotating the hammer sear main body 72 on the trip pin 50 against the bias of the sear trip return spring 93 to move the sear block 78 out of the way of the hook 87 as the hammer 14 pivots rearward. The sear trip return spring 93 then biases the sear trip 32 toward the active position and, through the sear trip 32 and hammer sear stud 80, biases the hammer sear 30 back into the engaged position. Once the bolt carrier 12 has moved far enough rearward to release the hammer 14, as shown in FIG. 22 , the hammer spring (omitted for clarity) biases the hammer 14 back toward the fired position, which causes the automatic sear surface 84 on the hook 87 of the hammer 14 to engage the hammer sear surface 82 on the sear block 78. The hammer 14 is now in the automatic cocked position. The hammer sear 30 prevents the hammer 14 from moving forward to fire the weapon 2 until the bolt carrier 12 contacts the sear trip 32 as described. This prevents undesirable “hammer follow” during reciprocation of the bolt carrier 12. FIGS. 23A-24 depict the bolt carrier 12 approaching the in-battery position with the trigger 20 in the pulled position while the hammer 14 remains retained in the automatic cocked position by the hammer sear 30. During this stage of operation, the sear trip 32 is in the active position about to be tripped by the boss 100 on the bolt carrier 12 when the bolt carrier 12 reaches the in-battery position.
FIG. 24 illustrates via arrows the mechanical sequence of events that occur upon the bolt carrier 12 reaching the in-battery position when the hammer 14 is in the automatic cocked position. First, upon the bolt carrier 12 reaching the in-battery position, the boss 100 contacts the protrusion 90 of the sear trip 32 and moves the sear trip 32 longitudinally forward against the bias of the return spring 93 into the tripped position (see Arrow 1). Movement of the sear trip 32 into the tripped position caused the hammer sear 30 to rotate about the trip pin 50. Rotation of the hammer sear 30 moves the sear block 78 and the hammer sear surface 82 out of engagement with the automatic sear surface 84 on the hook 87 of the hammer 14 (see Arrow 2). This allows the constant bias of the hammer spring 33 to rapidly pivot the hammer 14 to the fired position (see Arrow 3). FIGS. 25A-25B accordingly depict the bolt carrier 12 in the in-battery position, the sear trip 32 in the tripped position, and the hammer 14 in the fired position with the trigger still in the pulled position. Continuing to hold the trigger 20 in the pulled position will cause the trigger mechanism 10 to reset the hammer to the automatic cocked position, as shown as FIG. 26 , and continue to fire until the trigger is released or the supply of ammunition is exhausted. If the trigger 20 is released after one or more shots are fired in automatic fire mode, the bolt carrier 12 will reset the hammer 14 to the automatic cocked position and lock in the open position as shown in FIG.
Specifically, upon releasing the trigger 20, the carrier sear compression spring 70 biases the carrier sear 28 upwardly into the engaged position wherein the carrier sear 28 engages the sear notch 125 to prevent the bolt carrier 12 from moving forward into battery and tripping the sear trip 32 to continue firing. In this way, the spring 70 pivots the carrier sear 28 about pin 60 and lowers the fork 62 of the sear arm 26 down on the cross member 58 of the trigger 20, placing the sear arm 26 in the ready position. The weapon 2 is ready to fire from the open bolt position upon subsequent depression of the trigger 20. Pulling the trigger 20 again will pivot the carrier sear 28 to the disengaged position and begin the automatic firing sequence by releasing the bolt carrier 12 to move forward and trip the sear trip 32 while moving into battery, as described above.
The fire control housing 4, pistol grip 6, bolt carrier 12, trigger housing 15, and various other components of the trigger mechanism 10 can be formed from any suitably durable and lightweight material(s) known to ordinarily skilled artisans.
Although embodiments of the present invention have been described in detail, it will be understood by those skilled in the art that various modifications can be made therein without departing from the spirit and scope of the invention as set forth in the appended claims.
This written description uses examples to disclose the invention and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
It will be understood that the particular embodiments described herein are shown by way of illustration and not as limitations of the invention. The principal features of this invention may be employed in various embodiments without departing from the scope of the invention. Those of ordinary skill in the art will recognize numerous equivalents to the specific apparatus and methods described herein. Such equivalents are considered to be within the scope of this invention and are covered by the claims. For example, additional firing modes such as open bolt semiautomatic fire and closed bolt automatic fire are contemplated here and achievable simply by rearranging the surface geometries (i.e., cam profiles) on the selector barrel 40 to appropriately move the other operational components of the trigger mechanism 10 (e.g., hammer sear 30, sear trip 32, sear arm 26 and carrier sear 28).
All of the compositions and/or methods disclosed and claimed herein may be made and/or executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of the embodiments included herein, it will be apparent to those of ordinary skill in the art that variations may be applied to the compositions and/or methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit, and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope, and concept of the invention as defined by the appended claims.
Thus, although there have been described particular embodiments of the present invention, it is not intended that such references be construed as limitations upon the scope of this invention except as set forth in the following claims.

Claims

What is claimed is:

1. A trigger mechanism for a firearm having a bolt carrier that reciprocates and pivotally displaces a hammer when cycled, the trigger mechanism comprising:

a selector operable between a safe position, a semiautomatic position, and an automatic position;

a trigger pivotable between a set position and a pulled position;

a disconnector pivotably connected to the trigger and pivotable via the selector between a working position in which the disconnector is in a path of the hammer, and a retracted position in which the disconnector is out of the path of the hammer;

a carrier sear pivotable between a disengaged position and an engaged position in which the carrier sear is arranged to engage the bolt carrier, the carrier sear biased toward the engaged position when the selector is in the automatic position and the trigger is not in the pulled position; and

a sear arm pivotably connected to the carrier sear and movable by pulling the trigger when the selector is in the automatic position to pivot the carrier sear toward the disengaged position.

2. The trigger mechanism of claim 1, wherein the selector is rotatable to pivot the disconnector.

3. The trigger mechanism of claim 1, wherein when the selector is in the automatic position, the disconnector is in the retracted position.

4. The trigger mechanism of claim 1, wherein when the selector is in the semiautomatic position, the disconnector is biased toward the working position.

5. The trigger mechanism of claim 1, wherein moving the selector from the automatic position to the semiautomatic position pivots the disconnector from the retracted position to the working position.

6. The trigger mechanism of claim 1, wherein the carrier sear is biased toward the engaged position when the selector is in the safe position.

7. The trigger mechanism of claim 1, wherein the selector is rotatable to move the sear arm between a ready position in which the sear arm is arranged to pivot the carrier sear toward the disengaged position when the trigger is pulled, and a static position in which the sear arm is arranged so as not to pivot the carrier sear toward the disengaged position when the trigger is pulled.

8. The trigger mechanism of claim 7, wherein:

when the selector is in the automatic position, the sear arm is in the ready position; and

when the selector is in the semiautomatic position, the sear arm is in the static position.

9. The trigger mechanism of claim 7, wherein:

the selector defines a plurality of cam profiles; and

one cam profile controls movement of both the disconnector and the sear arm simultaneously.

10. The trigger mechanism of claim 9, wherein:

when the selector is rotated to the automatic position, the cam profile moves the disconnector to the retracted position and the sear arm to the ready position; and

when the selector is rotated to the semiautomatic position, the cam profile moves the disconnector to the working position and the sear arm to the static position.

11. The trigger mechanism of claim 7, wherein:

the trigger includes a slot and a cross member;

the sear arm defines a fork and a spur;

the fork is arranged in the slot with the cross member received in the fork;

the spur is arranged to ride on the selector;

rotation of the selector to the automatic position moves the spur into a recess of the selector and seats the fork on the cross member; and

rotation of the selector to the semiautomatic position moves a cam lobe on the selector into contact with the spur to space the fork from the cross member.

12. The trigger mechanism of claim 1, wherein the bolt carrier can be moved from an in-battery position to an open position when the selector is in the safe position.

13. The trigger mechanism of claim 1, wherein the carrier sear retains the bolt carrier in an open position when the carrier sear engages the bolt carrier.

14. The trigger mechanism of claim 13, wherein moving the selector from the automatic position to the semiautomatic position while the carrier sear is in the engaged position pivots the carrier sear from the engaged position to the disengaged position to release the bolt carrier from the open position toward an in-battery position.

15. The trigger mechanism of claim 1, further comprising a trigger housing in which the selector, the trigger, the hammer, the disconnector, the carrier sear, and the sear arm are mounted, wherein the selector extends through a pair of transversely aligned selector openings in sidewalls of the trigger housing such that the selector is manually operable from two opposing sides of the trigger housing.

16. A machine gun comprising the trigger mechanism of claim 1.

17. A trigger mechanism for a firearm having a bolt carrier that reciprocates and pivotally displaces a hammer when cycled, the trigger mechanism comprising:

a selector operable between a safe position, an automatic position, and a semiautomatic position;

a trigger pivotable between a set position and a pulled position;

a hammer pivotable between a fired position and at least one cocked position, the hammer biased toward the fired position;

a hammer sear rotatable via the selector between a disengaged position and an engaged position in which the hammer sear is arranged to engage the hammer, wherein the hammer sear is biased toward the engaged position when the selector is in the automatic position; and

a sear trip connected to the hammer sear and movable via the hammer sear between an inactive position and an active position in which the sear trip is arranged to be contacted by the bolt carrier when the bolt carrier reaches a substantially in-battery position, wherein:

the sear trip is biased toward the active position when the selector is in the automatic position, and

contact by the bolt carrier with the sear trip moves the sear trip against the bias to disengage the hammer sear from the hammer.

18. The trigger mechanism of claim 17 further comprising a bolt carrier defining a boss configured to contact the sear trip when the sear trip is in the active position and the bolt carrier reaches the substantially in-battery position.

19. The trigger mechanism of claim 17, further comprising:

a trigger housing containing the selector, the trigger, the hammer, and the hammer sear;

wherein the sear trip is an elongated member slidably mounted on the trigger housing and constrained to longitudinally reciprocating motion.

20. The trigger mechanism of claim 19, wherein the sear trip includes a protrusion configured to be contacted by the bolt carrier when the bolt carrier reaches the substantially in-battery position and the sear trip is in the active position.

21. The trigger mechanism of claim 17, wherein the hammer sear is biased into contact with the selector via the sear trip.

22. The trigger mechanism of claim 21, wherein:

the hammer sear includes a finger; and

the finger is biased into contact with the selector via the sear trip.

23. The trigger mechanism of claim 22, wherein:

the finger rides in a recess on the selector when the hammer sear is in the engaged position.

24. The trigger mechanism of claim 17, wherein pivotal displacement of the hammer by the bolt carrier when the selector is in the automatic position and the trigger is in the pulled position causes the hammer to rotate the hammer sear out of the engaged position against the bias until continued displacement of the hammer allows the bias to return the hammer sear to the engaged position whereby the hammer is prevented from moving toward the fired position until the bolt carrier contacts the sear trip.

25. The trigger mechanism of claim 17, further comprising:

26. The trigger mechanism of claim 17, further comprising:

a disconnector pivotably connected to the trigger and pivotable via the selector between a working position in which the disconnector is in a path of the hammer, and a retracted position in which the disconnector is out of the path of the hammer.

27. A machine gun comprising the trigger mechanism of claim 17.

28. A trigger mechanism for a firearm having a bolt carrier that reciprocates and pivotally displaces a hammer when cycled, the trigger mechanism comprising:

a selector rotatable between a safe position, an automatic position, and a semiautomatic position;

a trigger having a trigger sear and pivotable between a set position and a pulled position;

a hammer pivotable between a fired position, a semiautomatic cocked position, and an automatic cocked position, the hammer biased toward the fired position;

a sear trip connected to the hammer sear and movable via the hammer sear between an inactive position and an active position in which the sear trip is arranged to be contacted by the bolt carrier when the bolt carrier reaches a substantially in-battery position during cycling thereof, wherein:

contact by the bolt carrier with sear trip moves the sear trip against the bias to disengage the hammer sear from the hammer and release the hammer toward the fired position;

wherein pulling and holding the trigger in the pulled position when the selector is in the automatic position, the bolt carrier is in a substantially in-battery position, and the hammer is in the semiautomatic cocked position, releases the hammer toward the fired position and transitions control of the hammer from the trigger sear to the hammer sear.