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 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: Systems, methods, and apparatus for an ejection port cover with a multifunctional pin. In one embodiment, a fixed pin and a spring-loaded pin both mate with hinge openings at ends of the ejection port. The spring-loaded pin can be longitudinally biased by a spring, such as a torsion spring. This same spring can perform biasing of the ejection port cover toward an open position as well as biasing of a flag extending from the spring-loaded pin into a locked position when the ejection port cover is not installed.

Abstract: A sighting system for a firearm and related methods are disclosed. The sighting system has front and rear flip-up sights, wherein the front sight comprises a flip-up portion having an aperture through which a sight post can partially extend; a knob comprising one or more notches on a first side and the sight post extending from a second side; at least one detent arranged to face and interact with the one or more notches. The knob is configured to rotate about a first axis, where the rotation causes the sight post to move in a first direction along the first axis; tilting of the knob in a second direction based on the detent interfacing with the notches; and tilting of the sight post in the second direction, thereby forcing at least a portion of the sight post to press against the aperture, or a combination thereof.

Abstract: A firearm magazine assembly and a related method are disclosed. The follower has a top platform, a proximal end, a distal end, and at least one slider rail on a first side of the follower. At least a portion of the at least one slider rail is at a position that is between and remote from both the proximal end of the follower and the distal end of the follower. The housing is shaped to receive the follower. The housing has a first wall having a first recess for receiving the at least one slider rail, the first recess defined by opposing surfaces. At least a portion of the at least one slider rail is shaped to engage the two opposing surfaces to limit tilt of the follower.

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: 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: 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: The present disclosure describes a foldable firearm that collapses into a folded state under spring pressure. The foldable firearm may include a foldable grip assembly. The foldable grip assembly may include a foldable pistol grip, a foldable trigger assembly, a folding bar, and a foldable hand stop. The foldable grip assembly may fold into the top shell of the foldable firearm. The foldable firearm may also include an ambidextrous charging handle assembly that may include a bottom portion, a top portion, a guide bar, and two opposing charging handles. The charging handles may be pulled to unfold the foldable firearm, and/or butterflied such that pivoting one charging handle causes the other charging handle to pivot. The first-pivoted charging handle may then be pulled rearwards to unfold the firearm. The first-pivoted charging handle may then be pulled further rearwards to rack the slide of the foldable firearm.

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 firearm barrel tray having a barrel channel and a firearm accessory mounting interface, wherein the firearm barrel tray is configured to be attached to a firearm stock such that the barrel channel sits on a first side of the firearm stock and the firearm accessory mounting interface is configured to align with a recess on a second side of the firearm stock.

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.