In one aspect the invention provides a firearm assembly comprising a barrel, receiver and stock, wherein the assembly comprises a first fastener operable to fasten a first section of the receiver so as to locate the receiver in the stock and so as to align the receiver with the stock, wherein the assembly further comprises a second fastener operable to fix a second section of the receiver in place relative to the stock and wherein the second fastener is adjustable to fix the second section of the receiver in place without applying stress to the receiver. Embodiments of this invention may allow fixing a second section in place relative to the stock which place the second section of the receiver assumes naturally when the first part of the receiver is located and aligned by the first fastener.

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.

A two-piece barrel nut includes an internal nut with an externally threaded portion on one end and a plurality of engageable members on the opposite end, and an external nut with an internally threaded portion on one end that receives the externally threaded portion of the internal nut and one or more receptacles on the other end that each may receive a fastener that engages at least one of the plurality of engageable members on the internal nut to lock the external nut to the internal nut. A method for using the barrel nut to attach a barrel to a firearm is also disclosed.

The modular upper receiver assembly for firearms is an adapter allowing interchanging of barrels of different calibers to attach to an upper receiver assembly. The adapter assembly serves to provide a quick changeover coupling means for connecting an assortment of barrels of different calibers and lengths to the receiver. The coupling includes a barrel retaining bushing and adapter pair with threaded surfaces on the receiver for a threaded engagement, reinforced with threaded fastener compression for improved rigidity.

A device implementable on a firearm includes a monolithic upper receiver, comprising an upper receiver portion and a handguard portion, which is configured to accommodate non-proprietary barrel assemblies dimensioned according to United States military standard (mil-spec) barrel assembly dimensions and non-proprietary bolt carrier groups (BCGs) dimensioned according to mil-spec BCG dimensions. The device also includes a charging handle assembly configured to be coupled to an operating rod of a gas system of the firearm and forward of a BCG of the firearm. The device further includes a barrel locking system including a locking plate and a locking screw. When the locking screw is screwed into a threaded hole on the locking plate, the locking plate engages with a side of a barrel extension of the barrel assembly in a radial directions perpendicular to a longitudinal axis of the barrel assembly.

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.

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.

A link feed assembly. There is: a bolt carrier near a chamber of a modular weapon system; an infeed ramp, coupled to a first side of a weapon frame near the chamber; an outfeed ramp, coupled to a second side of the capon frame near the chamber and opposite the infeed ramp, positioned to form a space between the infeed ramp and the outfeed ramp; and a feed arm assembly coupled to the weapon frame and extending over the space between the infeed ramp and the outfeed ramp, the feed arm assembly functionally coupled to the bolt carrier such that cycling of the bolt carrier forward and backwards causes cycling of the feed arm assembly in a circuitous motion, the feed arm including a grabbing protrusion that is shaped to grab a top portion of a link during cycling of the feed arm assembly.

A rifle receiver arrangement including a hollow chamber with a silt to receive an end of a rifle barrel. A slit opening/closing arrangement including an abutment member to abut against a rotatable bolt once the rotatable bolt is rotated in a second direction beyond a first open position such that upon abutment between the rotatable bolt and the abutment member, further rotation of the rotatable bolt in the second direction increases the gap of the slit of the hollow chamber to provide an extended open position to allow the end of the rifle barrel to be accepted less restrictively into the hollow chamber.

A device implementable on a firearm includes a monolithic upper receiver, comprising an upper receiver portion and a handguard portion, which is configured to accommodate non-proprietary barrel assemblies dimensioned according to United States military standard (mil-spec) barrel assembly dimensions and non-proprietary bolt carrier groups (BCGs) dimensioned according to mil-spec BCG dimensions. The device also includes a charging handle assembly configured to be coupled to an operating rod of a gas system of the firearm and forward of a BCG of the firearm. The device further includes a barrel locking system including a locking plate and a locking screw. When the locking screw is screwed into a threaded hole on the locking plate, the locking plate engages with a side of a barrel extension of the barrel assembly in a radial directions perpendicular to a longitudinal axis of the barrel assembly.