An adjustable mount for a picatinny rail on a firearm, where the mount includes a vertically adjustable riser that will permit the mounted optic to co-witness with the back-up iron sights on the firearm.

A firearm as disclosures herein comprises a main receiver body, a barrel, a breech bolt structure, a buffer assembly, a trigger group assembly, a bolt catch and at least one of an auto-sear, a magazine adapter and a breech bolt anti-rotation structure. The main receiver body is preferably of a monolithic construction whereby the handguard and breech bolt carrying bore can be manufactured from a single piece of material. The auto-sear is tripped by engagement with a buffer of the buffer assembly. The magazine adapter has an exterior surface structure engaged with a mating interior surface structure of a magazine well space of the main receiver body. A distal end portion of the breech bolt anti-rotation structure is engageable by the buffer for limiting forward travel of the buffer when the barrel is detached from the main receiver body.

A firearm as disclosures herein comprises a main receiver body, a barrel, a breech bolt structure, a buffer assembly, a trigger group assembly, a bolt catch and at least one of an auto-sear, a magazine adapter and a breech bolt anti-rotation structure. The main receiver body is preferably of a monolithic construction whereby the handguard and breech bolt carrying bore can be manufactured from a single piece of material. The auto-sear is tripped by engagement with a buffer of the buffer assembly. The magazine adapter has an exterior surface structure engaged with a mating interior surface structure of a magazine well space of the main receiver body. A distal end portion of the breech bolt anti-rotation structure is engageable by the buffer for limiting forward travel of the buffer when the barrel is detached from the main receiver body.

An upper receiver assembly includes an outer member with an upper rail and an inner member with at least one of a pivot pin lug and a takedown pin lug. The inner member is disposed at least partially inside the outer member. The outer member includes an ejection port, and the inner member includes an ejection port. The ejection port of the inner member is at least partially aligned with the ejection port of the outer member.

An upper receiver assembly includes an outer member with an upper rail and an inner member with at least one of a pivot pin lug and a takedown pin lug. The inner member is disposed at least partially inside the outer member. The outer member includes an ejection port, and the inner member includes an ejection port. The ejection port of the inner member is at least partially aligned with the ejection port of the outer member.

An accessory control handgrip apparatus for weapon includes a rail clamp assembly, a grip base extending from the grip base assembly, a grip sleeve slidably received on the grip base, a keypad disposed on the grip sleeve, and one or more connectors for operably coupling the keypad to an accessory device.

An accessory control handgrip apparatus for weapon includes a rail clamp assembly, a grip base extending from the grip base assembly, a grip sleeve slidably received on the grip base, a keypad disposed on the grip sleeve, and one or more connectors for operably coupling the keypad to an accessory device.

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.

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.

In some embodiments, a crossbow comprises a stock, a bow portion, a latch, a trigger and a foregrip. In some embodiments, the foregrip is supported by the stock and arranged to move with respect to the stock between a first position and a second position.