Abstract: An accessory mounting interface for a firearm, and a related method, are disclosed. The interface has a firearm accessory, a first elongated fastener, and a second fastener rotationally mated to the first elongated fastener. The first elongated fastener has right-handed threading and is arranged through a through hole in the firearm accessory with a first end extending below first and second halves of a first slot protrusion of the firearm accessory. The second fastener has a length greater than a width, the length measured along a longitudinal axis of the second fastener, the second fastener having a plurality of straight edges. At least one of the plurality of straight edges prevents the second fastener from rotating further than a closed position when the at least one of the straight edges abuts a sidewall of an elongated slot in the firearm.

Abstract: Systems, methods, and apparatus are described for a locking folding knife having a handle lock and a safety switch arranged around and rotatable around a pivot axis of the knife. In an engaged position the switch overlaps at least a portion of the handle lock and prevents it from moving into an unlocked position. A spring, such as a wire form spring, can be arranged within a pocket of the switch, and when the switch is moved between engaged and disengaged positions the spring can be compressed generating a rotational bias on the switch urging the switch toward either the engaged or disengaged position.

Abstract: An interface for coupling a bipod to a sling stud of a firearm forend. The interface can include two pawls that pivot to release or grasp the sling stud. The pawls can be biased upward via a detent that rides within a vertical aperture in a pivot holder. The pivot holder can move up and down within a vertical aperture in a mounting plate of the interface, and via this movement the pawls may be forced open or closed. A bottom surface of one or both pawls can include an irregular surface different portions of which interface with a top of the detent depending on a vertical position of the pivot holder within the aperture in the mounting plate.

Abstract: An interface for coupling a bipod to a sling stud of a firearm forend. The interface can include two pawls that pivot to release or grasp the sling stud. The pawls can be biased upward via a detent that rides within a vertical aperture in a pivot holder. The pivot holder can move up and down within a vertical aperture in a mounting plate of the interface, and via this movement the pawls may be forced open or closed. A bottom surface of one or both pawls can include an irregular surface different portions of which interface with a top of the detent depending on a vertical position of the pivot holder within the aperture in the mounting plate.

Abstract: This disclosure describes a firearm stock or arm brace with an adjustable length of pull. The stock or arm brace can include a body and lower stock, where the body includes a buffer tube receiving aperture and the lower stock includes a hollow cavity with a plunger and two concentric springs therein. One or more buttons can be affixed to sides of the plunger in the hollow cavity that can be used to depress the plunger against the force of one or both of the springs. One of the two springs may be shorter than the other and have a greater spring constant than the longer spring. Depressing the plunger against the taller spring may allow a user to adjust the length of pull while greater pressure and engagement of the second spring allows the stock or arm brace to be removed from a buffer tube or receiver extension.

Abstract: This disclosure describes systems, methods, and apparatus for a bipod having pivot and cant functionality built into a unified cant/pivot assembly, housing, and pivot block. Rotation of a locking knob under the housing can gradually increase or decrease friction of the cant and pivoting degrees of freedom. Sufficient loosening of the locking knob can allow a pivot block to be lifted from the housing and rotated 180°, and then retightened to lock in a given pivot position. Before this 180 rotation of the pivot block, the pivot block and hence the firearm is free to pivot up to 10°, or up to 20°, or up to 30°.

Abstract: An interface for coupling a bipod to a sling stud of a firearm forend. The interface can include two pawls that pivot to release or grasp the sling stud. The pawls can be biased upward via a detent that rides within a vertical aperture in a pivot holder. The pivot holder can move up and down within a vertical aperture in a mounting plate of the interface, and via this movement the pawls may be forced open or closed. A bottom surface of one or both pawls can include an irregular surface different portions of which interface with a top of the detent depending on a vertical position of the pivot holder within the aperture in the mounting plate.

Abstract: A magazine assembly for a firearm and a related method are disclosed. The assembly has a magazine housing defining a track, and a follower assembly. The magazine housing is configured to constrain a cartridge as the cartridge is moved within the magazine assembly such that majority of a proximal surface area of the cartridge does not contact the magazine housing, and a distal tip of the cartridge does not contact the magazine housing.

Abstract: This disclosure describes systems, methods, and apparatus for a locking folding knife having a handle lock and a safety switch arranged around and rotatable around a pivot axis of the knife. In an engaged position the switch overlaps at least a portion of the handle lock and prevents it from moving into an unlocked position. A spring, such as a wire form spring, can be arranged within a pocket of the switch, and when the switch is moved between engaged and disengaged positions the spring can be compressed generating a rotational bias on the switch urging the switch toward either the engaged or disengaged position.

Abstract: An accessory mounting interface for a firearm, and a related method, are disclosed. The interface has a firearm accessory, a first elongated fastener, and a second fastener rotationally mated to the first elongated fastener. The first elongated fastener has right-handed threading and is arranged through a through hole in the firearm accessory with a first end extending below first and second halves of a first slot protrusion of the firearm accessory. The second fastener has a length greater than a width, the length measured along a longitudinal axis of the second fastener, the second fastener having a plurality of straight edges. At least one of the plurality of straight edges prevents the second fastener from rotating further than a closed position when the at least one of the straight edges abuts a sidewall of an elongated slot in the firearm.

Abstract: This disclosure describes systems, methods, and apparatus for a follower assembly comprising one or more dummy cartridges, the first thereof comprising an angled follower platform that when pressed between the follower spring and a final live cartridge in the magazine, rotates to a first side of the magazine and enhances follower interaction with a slide lock mechanism. The follower platform may also be angled back to front to further enhance this interaction. The follower platform may include a protruding heel extending laterally from a front portion of the first side of the follower platform configured to interface with the slide lock mechanism. A rear stop may extend from a rear portion of the first side and interface with a downward-facing surface of the magazine near the feed end, wherein contact between these two surfaces causes a front end of the first dummy cartridge to rotate upward.

Abstract: This disclosure describes systems, methods, and apparatus for detecting and displaying a number of rounds in a firearm magazine comprising a maximum number of N rounds. The magazine may comprise a follower, magnets on the follower, and <N magnetic-field-sensing sensors arranged along a path of the magnets when the follower moves along a length of the magazine, the sensors generating round count data based on a position of the one or more magnets relative to the <N magnetic-field-sensing sensors, and a first substantially flat antenna arranged on an inside of the magazine and configured to wirelessly transmit a round count indication to a second substantially flat antenna on the firearm, the round count indication based on the round count data, the second substantially flat antenna affixed to an inside of a magazine well of the firearm and mostly overlapping with the first substantially flat antenna.

Abstract: This disclosure describes systems, methods, and apparatus for a follower assembly comprising one or more dummy cartridges, the first thereof comprising an angled follower platform that when pressed between the follower spring and a final live cartridge in the magazine, rotates to a first side of the magazine and enhances follower interaction with a slide lock mechanism. The follower platform may also be angled back to front to further enhance this interaction. The follower platform may include a protruding heel extending laterally from a front portion of the first side of the follower platform configured to interface with the slide lock mechanism. A rear stop may extend from a rear portion of the first side and interface with a downward-facing surface of the magazine near the feed end, wherein contact between these two surfaces causes a front end of the first dummy cartridge to rotate upward.

Abstract: A magazine assembly for a firearm and a related method are disclosed. The assembly has a magazine housing defining a track, and a follower assembly. The magazine housing is configured to constrain a cartridge as the cartridge is moved within the magazine assembly such that majority of a proximal surface area of the cartridge does not contact the magazine housing, and a distal tip of the cartridge does not contact the magazine housing.

Abstract: This disclosure describes a firearm stock or arm brace with an adjustable length of pull. The stock or arm brace can include a body and lower stock, where the body includes a buffer tube receiving aperture and the lower stock includes a hollow cavity with a plunger and two concentric springs therein. One or more buttons can be affixed to sides of the plunger in the hollow cavity that can be used to depress the plunger against the force of one or both of the springs. One of the two springs may be shorter than the other and have a greater spring constant than the longer spring. Depressing the plunger against the taller spring may allow a user to adjust the length of pull while greater pressure and engagement of the second spring allows the stock or arm brace to be removed from a buffer tube or receiver extension.

Abstract: This disclosure describes systems, methods, and apparatus for detecting and displaying a number of rounds in a firearm magazine comprising a maximum number of N rounds. The magazine may comprise a follower, magnets on the follower, and <N magnetic switches arranged along a path of the magnets when the follower moves along a length of the magazine, the switches configured to activate based on a magnetic field exceeding a threshold, and a first antenna arranged on an inside of the magazine and parallel to a firing direction of the firearm, and configured to wirelessly transmit a round count indication to a second antenna on the firearm, the round count indication based on the round count data, the second antenna affixed to an inside of a magazine well of the firearm and mostly overlapping with the first antenna.

Abstract: This disclosure describes systems, methods, and apparatus for a locking folding knife having a handle lock and a safety switch arranged around and rotatable around a pivot axis of the knife. In an engaged position the switch overlaps at least a portion of the handle lock and prevents it from moving into an unlocked position. A spring, such as a wire form spring, can be arranged within a pocket of the switch, and when the switch is moved between engaged and disengaged positions the spring can be compressed generating a rotational bias on the switch urging the switch toward either the engaged or disengaged position.