Abstract: A castle nut has a groove around an exterior circumference thereof. An end plate has a through hole extending in a direction perpendicular to a longitudinal axis of a firearm. When a buffer tube is threaded onto a lower receiver of the firearm with the buffer tube traversing through the castle nut and the end plate, the castle nut can be screwed in a direction toward the lower receiver to fasten the end plate against the lower receiver. When the end plate is fastened against the lower receiver by the castle nut, the securing device can be screwed into the through hole of the end plate such that a portion of the securing device is engaged with the groove of the castle nut to prevent the castle nut to be loosened by being unscrewed in a direction away from the lower receiver.

Abstract: An apparatus implementable on a pistol includes a compensator and a guide rod. The guide rod has a front distal end and a rear distal end opposite the front distal end. The compensator includes a muzzle brake having a recoil-reduction device, a first through hole and a second through hole. When the compensator is implemented on the pistol: (a) the recoil-reduction device redirects propellant gases to counter a recoil force upon firing of a round of ammunition by the pistol; (b) the first through hole is aligned with a barrel of the pistol to allow firing of the round of ammunition, and (c) the second through hole receives the front distal end of the guide rod therein such that an interface between the guide rod, the muzzle brake and a slide of the pistol is keyed to prevent rotation of the guide rod.

Abstract: An apparatus implementable on a firearm includes a quick-detach (QD) handguard assembly which includes a handguard and a locking mechanism. The handguard has a hollow therein allowing the handguard to surround a barrel of the firearm with the barrel traversing through the hollow along a longitudinal axis of the handguard. The locking mechanism is coupled to the handguard. The locking mechanism includes a QD lever configured to lock the handguard to a barrel nut of the firearm and unlock the handguard from the barrel nut.

Abstract: A detachable firearm attachment implementable on a firearm includes a main body having a firearm attachment side and an accessory attachment side. The firearm attachment side is configured to attach to a surface of a part of the firearm. The accessory attachment side includes a socket configured such that a detachable device is coupled to and decoupled from the socket along an axis of the socket that is at an angle less than 90° from the surface of the part of the firearm. The socket is further configured with one or more indentation chambers on a surface of a cavity of the socket in which the detachable device is received when the detachable device is coupled to the socket such that, when the detachable device is coupled to the socket, a rotation of the detachable device is prevented by the one or more indentation chambers.

Abstract: A scope mount implementable on a firearm includes a base and an adjustable cantilever. The base has a first primary side and a second primary side opposite the first primary side, with the second primary side configured to accommodate and mount onto a rail on the firearm. The adjustable cantilever is slidingly installable on the first primary side of the base and is configured with a scope mounting feature to receive a scope thereon. The adjustable cantilever can be fixable at one of plural positions along a longitudinal axis of the base and on the base such that a total length of the scope mount, measured from one distal end of the scope mount to an opposite distal end of the scope mount, varies between a shortest length and a longest length according to at which one of the positions on the base the adjustable cantilever is fixed.

Abstract: An apparatus implementable on a firearm may include a takedown pin and a pivot pin. The takedown pin holds together a rear portion of lower and upper receivers of the firearm. The pivot pin holds together a front portion of lower and upper receivers of the firearm. Each of the takedown pin and pivot pin respectively includes a head and a generally cylindrical shank extending from the head toward a distal end thereof opposite the head. The shank is configured with: (1) a first groove track extending along a longitudinal axis of the shank, (2) a second groove track parallel to the first groove track and extending along the longitudinal axis of the shank, and (3) a linking groove track extending around the longitudinal axis of the shank and linking the first groove track and the second groove track.

Abstract: Various examples of a modular trigger control unit for firearms are described. A trigger mechanism housing, as part of the modular trigger control unit, can be removably received in a grip frame of a semi-automatic firearm such that, when received in the grip frame, a serial number of the firearm displayed on the trigger mechanism housing faces a back side of the grip frame and is visible through an opening on the back side of the grip frame.

Abstract: Examples of a self-releasing magazine and a magazine follower assembly thereof for firearms are described. The magazine follower assembly includes a casing and a self-releasing actuator received in the casing. When in use, the magazine follower assembly generally moves along a first axis with respect to the casing between a first position in the magazine when the magazine is fully loaded and a second position in the magazine when the magazine contains no ammunition cartridge. When the magazine follower assembly is at the second position in the magazine, the self-releasing actuator is configured to actuate a magazine release mechanism of the firearm to disengage the magazine from the firearm so that the magazine is detachable from the firearm.

Abstract: Various examples of a modular trigger control unit for firearms are described. The trigger control unit can be removably installed on a grip frame and installed between the grip frame and a slide assembly of a semi-automatic firearm. The trigger control unit includes at least a trigger pin and a trigger pivotable around the trigger pin when pulled. In response to the trigger being pulled by a user when the trigger control unit is installed between the grip frame and the slide assembly, a firing pin lug of a striker-firing mechanism in the slide assembly is released thereby allowing a striker of the striker-firing mechanism to move forward with respect to the slide assembly. Moreover, the trigger control unit is secured to the grip frame at least by the trigger pin such that removal of the trigger control unit from the grip frame requires removal of the trigger pin.

Abstract: Adjusting the length of firearms using stock assembly systems are provided. In one embodiment, a stock assembly comprises: a receiver extension having a first interface configured to mate with a second interface of a stock; the first interface comprising a base portion, a plurality of first edges, and a plurality of first grooves; the second interface comprising a slot portion, a plurality of second edges, and a plurality of second grooves; wherein the plurality of first edges are in contact with the plurality of second grooves and the plurality of first grooves are in contact with the plurality of second edges of the second interface to mate the stock with the receiver extension; and wherein the base portion of the first interface is in contact with the slot portion of the second interface allowing the stock to slide along a horizontal axis of the receiver extension.

Abstract: A castle nut has a groove around an exterior circumference thereof. An end plate has a through hole extending in a direction perpendicular to a longitudinal axis of a firearm. When a buffer tube is threaded onto a lower receiver of the firearm with the buffer tube traversing through the castle nut and the end plate, the castle nut can be screwed in a direction toward the lower receiver to fasten the end plate against the lower receiver. When the end plate is fastened against the lower receiver by the castle nut, the securing device can be screwed into the through hole of the end plate such that a portion of the securing device is engaged with the groove of the castle nut to prevent the castle nut to be loosened by being unscrewed in a direction away from the lower receiver.

Abstract: An apparatus implementable on a firearm may include a takedown pin and a pivot pin. The takedown pin holds together a rear portion of lower and upper receivers of the firearm. The pivot pin holds together a front portion of lower and upper receivers of the firearm. Each of the takedown pin and pivot pin respectively includes a head and a generally cylindrical shank extending from the head toward a distal end thereof opposite the head. The shank is configured with: (1) a first groove track extending along a longitudinal axis of the shank, (2) a second groove track parallel to the first groove track and extending along the longitudinal axis of the shank, and (3) a linking groove track extending around the longitudinal axis of the shank and linking the first groove track and the second groove track.

Abstract: An apparatus implementable on a pistol includes a compensator and a guide rod. The guide rod has a front distal end and a rear distal end opposite the front distal end. The compensator includes a muzzle brake having a recoil-reduction device, a first through hole and a second through hole. When the compensator is implemented on the pistol: (a) the recoil-reduction device redirects propellant gases to counter a recoil force upon firing of a round of ammunition by the pistol; (b) the first through hole is aligned with a barrel of the pistol to allow firing of the round of ammunition, and (c) the second through hole receives the front distal end of the guide rod therein such that an interface between the guide rod, the muzzle brake and a slide of the pistol is keyed to prevent rotation of the guide rod.

Abstract: A firearm blast reduction device installable on a muzzle of a firearm may include a lock device, a muzzle device and a muzzle shroud. When assembled together, the muzzle shroud faces a front side of the firearm and the muzzle device faces a rear side of the firearm, with the lock device received in the muzzle device and between the muzzle device and the muzzle shroud. To install, the muzzle shroud is rotated in one direction to lock the firearm blast reduction device on the muzzle. To uninstall, the muzzle shroud is rotated in an opposite direction to release the firearm blast reduction device from the muzzle.

Abstract: An apparatus implementable on a firearm may include a takedown pin and a pivot pin. The takedown pin holds together a rear portion of lower and upper receivers of the firearm. The pivot pin holds together a front portion of lower and upper receivers of the firearm. Each of the takedown pin and pivot pin respectively includes a head and a generally cylindrical shank extending from the head toward a distal end thereof opposite the head. The shank is configured with: (1) a first groove track extending along a longitudinal axis of the shank, (2) a second groove track parallel to the first groove track and extending along the longitudinal axis of the shank, and (3) a linking groove track extending around the longitudinal axis of the shank and linking the first groove track and the second groove track.

Abstract: Examples of a self-releasing magazine and a magazine follower assembly thereof for firearms are described. The magazine follower assembly includes a casing and a self-releasing actuator received in the casing. When in use, the magazine follower assembly generally moves along a first axis with respect to the casing between a first position in the magazine when the magazine is fully loaded and a second position in the magazine when the magazine contains no ammunition cartridge. When the magazine follower assembly is at the second position in the magazine, the self-releasing actuator is configured to actuate a magazine release mechanism of the firearm to disengage the magazine from the firearm so that the magazine is detachable from the firearm.

Abstract: A detachable firearm attachment implementable on a firearm may include a main body and a fastening device. The main body may have a first primary side and a second primary side. The first primary side may be configured to attach to both a first handguard rail system of a first handguard of the firearm and a second handguard rail system of a second handguard of the firearm. The fastening device may be configured to fasten the main body to the first handguard and the second handguard. The first handguard may include a plurality of first openings of a first shape with first dimensions. The second handguard may include a plurality of second openings of a second shape with second dimensions. The first shape and the second shape may be different. The first dimensions and the second dimensions may be different.

Abstract: A firearm accessory connecting device to be mounted on a rail interface system has two locking mechanism and alignment relief lugs by which the device can be aligned and secured onto either a KeyMod rail interface or an M-LOK rail interface. The two locking mechanisms situated at a first front-end and a second rear-end of the connecting device and defined by a screw hole whereby a screw will engage the top surface of the connecting device and extend through the screw hole to the interior surface of the rail interface wherein a nut will be used to secure the screw in position and hence the mount onto the rail. The alignment lugs located at specific distances along the bottom surface of the connecting device will be slidably attached and aligned onto the rail interface.