A firearm is described herein. The firearm comprises a receiver assembly adapted to receive a cartridge, a bolt assembly including a firing device operable to fire the cartridge, a barrel adapted to receive the projectile after the cartridge is fired, and a gas assembly including a gas tube. The receiver assembly includes an upper receiver portion, a lower receiver portion, and an upper receiver cover. The upper receiver portion defines a longitudinal axis, and an indexing slot operable to receive the gas tube. The upper receiver portion includes at least one integrated exterior track extending generally parallel to the longitudinal axis adapted to slidably couple with the upper receiver cover and a plurality of interior tracks extending generally parallel to the longitudinal axis adapted to slidably couple with the bolt assembly. The upper and lower receiver portions are pivotally connected to one another.

An upper receiver and barrel assembly includes an upper receiver, a barrel assembly and a gas piston assembly. An upper receiver housing receives a shotgun shell cartridge and the bolt carrier group includes a bolt carrier, a bolt within the bolt carrier, a firing pin and an ejector pin to expel fired shells. The barrel assembly includes a barrel, a barrel extension and a barrel nut to secure the barrel and barrel extension to the upper receiver housing. The gas piston assembly includes a piston body, a piston end cap and a piston bonnet configured to slidably receive the piston end cap therein. A piston gap is defined between the piston end cap and the bonnet end wall. The barrel defines a gas port fluidly connecting the open bore of the barrel with the piston gap. A biasing member urges the piston toward the bonnet.

An upper receiver and barrel assembly includes an upper receiver, a barrel assembly and a gas piston assembly. An upper receiver housing receives a shotgun shell cartridge and the bolt carrier group includes a bolt carrier, a bolt within the bolt carrier, a firing pin and an ejector pin to expel fired shells. The barrel assembly includes a barrel, a barrel extension and a barrel nut to secure the barrel and barrel extension to the upper receiver housing. The gas piston assembly includes a piston body, a piston end cap and a piston bonnet configured to slidably receive the piston end cap therein. A piston gap is defined between the piston end cap and the bonnet end wall. The barrel defines a gas port fluidly connecting the open bore of the barrel with the piston gap. A biasing member urges the piston toward the bonnet.

A semi-automatic or automatic rifle comprising a barrel attached to and upper receiver and including a compressible bolt carrier extension system. The compressible bolt carrier extension system includes a bolt carrier, an extension spring, two pins, and a reciprocation bolt carrier extension piece. As a whole, the compressible bolt carrier extension system makes possible the use of elongated upper and lower receivers to be used for chambering long-action or other center fire cartridges for use with AR rifles such as the M-16, and M4 etc., eliminating the need for any buffer or buffer tubes other than those commercially available. A further advantage of the compressible bolt carrier extension system is the reduction of felt recoil as the system fully loads during the recoil stroke as it pushes against the buffer absorbing additional recoil energy. The system can be incorporated into firearms using a variety of cartridges.

A semi-automatic or automatic rifle comprising a barrel attached to and upper receiver and including a compressible bolt carrier extension system. The compressible bolt carrier extension system includes a bolt carrier, an extension spring, two pins, and a reciprocation bolt carrier extension piece. As a whole, the compressible bolt carrier extension system makes possible the use of elongated upper and lower receivers to be used for chambering long-action or other center fire cartridges for use with AR rifles such as the M-16, and M4 etc., eliminating the need for any buffer or buffer tubes other than those commercially available. A further advantage of the compressible bolt carrier extension system is the reduction of felt recoil as the system fully loads during the recoil stroke as it pushes against the buffer absorbing additional recoil energy. The system can be incorporated into firearms using a variety of cartridges.

A semi-automatic or automatic rifle comprising a barrel attached to and upper receiver and including a compressible bolt carrier extension system. The compressible bolt carrier extension system includes a bolt carrier, an extension spring, two pins, and a reciprocation bolt carrier extension piece. As a whole, the compressible bolt carrier extension system makes possible the use of elongated upper and lower receivers to be used for chambering long-action or other center fire cartridges for use with AR rifles such as the M-16, and M4 etc., eliminating the need for any buffer or buffer tubes other than those commercially available. A further advantage of the compressible bolt carrier extension system is the reduction of felt recoil as the system fully loads during the recoil stroke as it pushes against the buffer absorbing additional recoil energy. The system can be incorporated into firearms using a variety of cartridges.

A semi-automatic or automatic rifle comprising a barrel attached to and upper receiver and including a compressible bolt carrier extension system. The compressible bolt carrier extension system includes a bolt carrier, an extension spring, two pins, and a reciprocation bolt carrier extension piece. As a whole, the compressible bolt carrier extension system makes possible the use of elongated upper and lower receivers to be used for chambering long-action or other center fire cartridges for use with AR rifles such as the M-16, and M4 etc., eliminating the need for any buffer or buffer tubes other than those commercially available. A further advantage of the compressible bolt carrier extension system is the reduction of felt recoil as the system fully loads during the recoil stroke as it pushes against the buffer absorbing additional recoil energy. The system can be incorporated into firearms using a variety of cartridges.

A firearm including a gas drive, having an annular piston which is displaceably arranged on the barrel to form an expansion chamber between two end positions. At least one gas port penetrates the wall of the barrel in the region of the expansion chamber and a selector is provided. In order to provide a simple and easily adjustable mechanism, the expansion chamber is delimited by a ring surface and an inner cylinder surface of the piston, an end surface of the selector and the barrel. The selector is rotatably arranged on the barrel with at least two predefined rest positions. In each rest position, the gas flow from the expansion chamber is delimitable by at least one selector opening formed on the selector.

A firearm including a gas drive, having an annular piston which is displaceably arranged on the barrel to form an expansion chamber between two end positions. At least one gas port penetrates the wall of the barrel in the region of the expansion chamber and a selector is provided. In order to provide a simple and easily adjustable mechanism, the expansion chamber is delimited by a ring surface and an inner cylinder surface of the piston, an end surface of the selector and the barrel. The selector is rotatably arranged on the barrel with at least two predefined rest positions. In each rest position, the gas flow from the expansion chamber is delimitable by at least one selector opening formed on the selector.

A semi-automatic or automatic rifle comprising a barrel attached to and upper receiver and including a compressible bolt carrier extension system. The compressible bolt carrier extension system includes a bolt carrier, an extension spring, two pins, and a reciprocation bolt carrier extension piece. As a whole, the compressible bolt carrier extension system makes possible the use of elongated upper and lower receivers to be used for chambering long-action or other center fire cartridges for use with AR rifles such as the M-16, and M4 etc., eliminating the need for any buffer or buffer tubes other than those commercially available. A further advantage of the compressible bolt carrier extension system is the reduction of felt recoil as the system fully loads during the recoil stroke as it pushes against the buffer absorbing additional recoil energy. The system can be incorporated into firearms using a variety of cartridges.