A handguard assembly for installation on a firearm includes a handguard, an index block, a first fastener, and a second fastener. The handguard includes first and second clearance apertures and the index block includes first and second threaded apertures. The first and second fasteners extend through the respective first and second clearance apertures and threaded into the respective first and second threaded apertures. The first and second fasteners define respective first and second longitudinal axes that are non-parallel and non-collinear with each other. Tightening the first and second fasteners with respect to the index block secures the handguard to the index block and prevents movement of the handguard relative firearm.

Quick take-down firearms and methods of using quick-take down firearms. The quick-take down includes an upper receiver coupling and a barrel coupling. The quick take-down can be unlocked by sliding a sliding lock collar in a translational motion to an unlocked position to release locking elements from a locked configuration. In the unlocked position, a barrel and handguard may be installed onto and removed from the upper receiver of the firearm. Releasing the sliding lock collar returns it to a locked position, securing the barrel and handguard to the upper receiver.

A firearm assembly has a barrel and a barrel receiving unit for receiving the barrel. A primary barrel nut is disposed over the barrel and mating with the barrel receiving unit. A primary end of the barrel is mated to a barrel extension. The primary barrel nut has an internal shoulder making contact with a shoulder of the barrel extension. A secondary barrel nut is disposed over the barrel and mating with the primary barrel nut to align the barrel with the barrel receiving unit. The internal shoulder of the primary barrel nut and the shoulder of the barrel extension can be flat or beveled. The secondary barrel nut has an internal shoulder contacting a shoulder of the barrel. The internal shoulder of the secondary barrel nut and the shoulder of the barrel are beveled or tapered.

A firearm assembly has a barrel and a barrel receiving unit for receiving the barrel. A primary barrel nut is disposed over the barrel and mating with the barrel receiving unit. A primary end of the barrel is mated to a barrel extension. The primary barrel nut has an internal shoulder making contact with a shoulder of the barrel extension. A secondary barrel nut is disposed over the barrel and mating with the primary barrel nut to align the barrel with the barrel receiving unit. The internal shoulder of the primary barrel nut and the shoulder of the barrel extension can be flat or beveled. The secondary barrel nut has an internal shoulder contacting a shoulder of the barrel. The internal shoulder of the secondary barrel nut and the shoulder of the barrel are beveled or tapered.

A heat dissipation assembly for use with a barrel forming a part of a firearm upper receiver. An annular shaped barrel nut is adapted to secure the barrel to the upper receiver. An elongated handguard is affixed to the barrel nut at a heat conducting location, the handguard adapted to surround a proximal extending portion of the barrel, the handguard having a plurality of apertures defined therethrough. At least one cooling element is located on an exterior of the handguard. A thermoelectric generator is incorporated into the handguard for transferring heat from the barrel nut to the cooling element. A fan component is integrated into the handguard and operated by the thermoelectric generator for drawing air through the apertures in order to provide additional cooling to the barrel.

A rotating bolt firearm may be configured to fire a .308 cartridge. However, the firearm may have a reduced weight in comparison to standard .308 rifles. The firearm may have many components typically used in a .223 rifle. The firearm may include a barrel extension with an extractor gap, which allows a .308 bolt to fit within a .223 sized barrel extension. The firearm may comprise an elongated magazine well in comparison to a .223 mil-spec rifle. The firearm may weigh less than 6.8 pounds with a 16-inch barrel, or less than 6.3 pounds with a 10.5 inch barrel.

A rotating bolt firearm may be configured to fire a .308 cartridge. However, the firearm may have a reduced weight in comparison to standard .308 rifles. The firearm may have many components typically used in a .223 rifle. The firearm may include a barrel extension with an extractor gap, which allows a .308 bolt to fit within a .223 sized barrel extension. The firearm may comprise an elongated magazine well in comparison to a .223 mil-spec rifle. The firearm may weigh less than 6.8 pounds with a 16-inch barrel, or less than 6.3 pounds with a 10.5 inch barrel.

Improved firearms including one or more of a removable and/or interchangeable top cover, an improved extractor mechanism, a striker safety mechanism with a direct trigger interface, a sear with direct striker interface, and/or a striker with integral striker spring retention features.

There is a multi-caliber weapon system. The multi-caliber weapon system comprises: a frame body, with a front body portion, a middle body portion, and a rear body portion, and including: a plurality of frame flanges, each frame flange being coupled to an interior of the frame body and extending upwardly therefrom; a barrel, removably coupled to the front body portion of the frame body, including: a plurality of barrel rings, each barrel ring being disposed around a circumference of the barrel and spaced along a length of the barrel, wherein the barrel rings are disposed on the frame flanges; a chamber, removably coupled to the middle body portion of the frame body, and removably coupled to the barrel; and a bolt, removably coupled to rear body portion of the frame body, removably coupled to the chamber, and including: a bolt face, removably coupled to a front bolt portion.

A secondary firearm with a rail mount attachable to a rail assembly of a primary firearm is disclosed. The secondary firearm comprises a body having at least one retaining pin hole and a bolt stop hole and a housing disposed about the body. The housing comprises at least one retaining pin aperture and/or a bolt stop aperture. The secondary firearm also includes at least one fastener disposed within at least one of the at least one retaining pin aperture and the at least one retaining pin hole and/or the bolt stop aperture and the bolt stop hole to fasten the housing to the body.