Select fire trigger mechanism for machine guns

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.

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:
 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.   
     
     
         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 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 during cycling thereof, 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 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.