Abstract: An upper receiver for a firearm, the upper receiver having: a hand guard section removably connected to the upper receiver via a locking mechanism pivotally mounted to the hand guard section for movement between a locking position and an unlocking position, wherein the locking mechanism requires only a single movement in one direction to move from the locking position to the unlocking position, wherein the hand guard section has peripheral device mounting rails located at a six o'clock position with respect to a centerline of the barrel and wherein the hand guard section is capable of being completely detached and removed from the upper receiver after the locking mechanism has been moved into the unlocking position; and a plurality of integrally formed rails located above the hand guard section and at three, nine and twelve o'clock positions with respect to the centerline of the barrel.

Abstract: An upper receiver for a firearm, the upper receiver having: a hand guard section removably connected to the upper receiver via a locking mechanism pivotally mounted to the hand guard section for movement between a locking position and an unlocking position, wherein the locking mechanism requires only a single movement in one direction to move from the locking position to the unlocking position, wherein the hand guard section has peripheral device mounting rails located at a six o'clock position with respect to a centerline of the barrel and wherein the hand guard section is capable of being completely detached and removed from the upper receiver after the locking mechanism has been moved into the unlocking position; and a plurality of integrally formed rails located above the hand guard section and at three, nine and twelve o'clock positions with respect to the centerline of the barrel.

Abstract: A rifle having a receiver with an integral hand guard and a barrel. The barrel is connected to the receiver. The hand guard extends over and surrounds the barrel. A removable hand guard is attached to the receiver by an attachment that stably holds the removable hand guard to the receiver. The attachment is arranged for allowing detachment and removal of the removable hand guard from the receiver without removal of fasteners.

Abstract: A rifle having a receiver with an integral hand guard and a barrel. The barrel is connected to the receiver. The hand guard extends over and surrounds the barrel. A removable hand guard is attached to the receiver by an attachment that stably holds the removable hand guard to the receiver. The attachment is arranged for allowing detachment and removal of the removable hand guard from the receiver without removal of fasteners.

Abstract: An indirect gas operating system for a semi-automatic or automatic rifle is provided, the indirect gas operating system having: a gas block secured to the rifle; a barrel secured to the rifle; a bolt carrier slidably received within a receiver of the rifle; a means for moving the bolt carrier within the receiver using gases discharged into a bore of the barrel of the rifle, wherein the means for moving is removably secured to the gas block such that the means for moving can be removed from the rifle through a forward end of the gas block without removing the gas block from the rifle; and an externally threaded barrel nut for securing the barrel to the receiver.

Abstract: An indirect gas operating system for a semi-automatic or automatic rifle is provided, the indirect gas operating system having: a gas block secured to the rifle; a barrel secured to the rifle; a bolt carrier slidably received within a receiver of the rifle; a means for moving the bolt carrier within the receiver using gases discharged into a bore of the barrel of the rifle, wherein the means for moving is removably secured to the gas block such that the means for moving can be removed from the rifle through a forward end of the gas block without removing the gas block from the rifle; and an externally threaded barrel nut for securing the barrel to the receiver.

Abstract: A rifle having a receiver with an integral hand guard and a barrel. The barrel is connected to the receiver. The hand guard extends over and surrounds the barrel. A removable hand guard is attached to the receiver by an attachment that stably holds the removable hand guard to the receiver. The attachment is arranged for allowing detachment and removal of the removable hand guard from the receiver without removal of fasteners.

Abstract: An indirect gas operating system for a semi-automatic or automatic rifle is provided, the indirect gas operating system having: a sleeve removably secured to a forward end of a gas block of the rifle; a piston slidably received within the gas block, wherein the gas block and the sleeve fluidly couple the piston to a bore of a barrel of the rifle; wherein an increase in pressure in the bore of the rifle causes the piston to move away from the sleeve; and wherein the sleeve and the piston are each capable of being removed from the rifle through the forward end of the gas block.

Abstract: An indirect gas operating system for a semi-automatic or automatic rifle is provided, the indirect gas operating system having: a sleeve removably secured to a forward end of a gas block of the rifle; a piston slidably received within the gas block, wherein the gas block and the sleeve fluidly couple the piston to a bore of a barrel of the rifle; wherein an increase in pressure in the bore of the rifle causes the piston to move away from the sleeve; and wherein the sleeve and the piston are each capable of being removed from the rifle through the forward end of the gas block.

Abstract: A rifle having a receiver with an integral hand guard and a barrel. The barrel is connected to the receiver. The hand guard extends over and surrounds the barrel. A removable hand guard is attached to the receiver by an attachment that stably holds the removable hand guard to the receiver. The attachment is arranged for allowing detachment and removal of the removable hand guard from the receiver without removal of fasteners.

Abstract: A semi-automatic or automatic rifle is provided the rifle having: a receiver having a hand guard portion; a barrel having a bore, the bore removably connected to the receiver, the hand guard portion surrounding at least a portion of the barrel; a gas block having a forward end and a rearward end aligned with the barrel; a sleeve removably secured to the forward end of the gas block; a piston slidably received within the gas block, wherein the gas block and the sleeve fluidly couple the piston to the bore of the barrel; wherein an increase in pressure in the bore of the barrel causes the piston to move away from the sleeve; and wherein the sleeve and the piston are each capable of being removed from the rifle through the forward end of the gas block without removing the gas block from the rifle.

Abstract: A semi-automatic or automatic rifle is provided the rifle having: a receiver having a hand guard portion; a barrel having a bore, the bore removably connected to the receiver, the hand guard portion surrounding at least a portion of the barrel; a gas block having a forward end and a rearward end aligned with the barrel; a sleeve removably secured to the forward end of the gas block; a piston slidably received within the gas block, wherein the gas block and the sleeve fluidly couple the piston to the bore of the barrel; wherein an increase in pressure in the bore of the barrel causes the piston to move away from the sleeve; and wherein the sleeve and the piston are each capable of being removed from the rifle through the forward end of the gas block without removing the gas block from the rifle.

Abstract: A rifle having a receiver with an integral hand guard and a barrel. The barrel is connected to the receiver. The hand guard extends over and surrounds the barrel. A removable hand guard is attached to the receiver by an attachment that stably holds the removable hand guard to the receiver. The attachment is arranged for allowing detachment and removal of the removable hand guard from the receiver without removal of fasteners.

Abstract: A semi-automatic or automatic rifle is provided. The semi-automatic or automatic rifle includes a receiver having an integral hand guard portion, a barrel having a bore. The bore is removably connected to the receiver, the hand guard portion extending over and surrounding the barrel, an indirect gas operating system has a gas block and a piston. The gas block has a cylinder, the gas block is fitted to the barrel, the cylinder is in communication with the bore. The piston has a piston end and a striking end, the piston end is fitted to the cylinder and has a bolt carrier having a striking surface. When a cartridge is fired, gas displaces the piston end and causes the striking end to strike the striking surface displacing the bolt assembly, wherein, the cylinder and the piston are together removable as an assembly from the firearm without disassembly of the rifle.

Abstract: A semi-automatic or automatic rifle is provided. The semi-automatic or automatic rifle includes a receiver having an integral hand guard portion, a barrel having a bore. The bore is removably connected to the receiver, the hand guard portion extending over and surrounding the barrel, an indirect gas operating system has a gas block and a piston. The gas block has a cylinder, the gas block is fitted to the barrel, the cylinder is in communication with the bore. The piston has a piston end and a striking end, the piston end is fitted to the cylinder and has a bolt carrier having a striking surface. When a cartridge is fired, gas displaces the piston end and causes the striking end to strike the striking surface displacing the bolt assembly, wherein, the cylinder and the piston are together removable as an assembly from the firearm without disassembly of the rifle.

Abstract: An indirect gas operating system for an M4 type automatic or semi-automatic firearm. The indirect gas operating system has a gas block having a cylinder. The gas block is fitted to a barrel assembly having a bore with the cylinder in communication with the bore. A piston having a piston end and a striking end has the piston end fitted to the cylinder. A bolt assembly having a striking surface is provided. When a cartridge is fired, gas displaces the piston end and causes the striking end to strike the striking surface displacing the bolt assembly. The cylinder and the piston are together removable as an assembly from the firearm without removal of the gas block.

Abstract: An M-4 firearm having a lower receiver assembly and an upper receiver assembly. The upper receiver assembly is connected to the lower receiver assembly. The lower receiver assembly has a fire control assembly. The upper receiver assembly has a barrel and a hand guard. The hand guard has a venting features for allowing cooling air to pass therethrough. The hand guard has a heat shield mounted therein. The hand guard has at least one peripheral device mounting rail. The hand guard has an upper portion and a removable lower portion. The removable lower portion has at least one peripheral device mounting rail. The removable lower portion may be removed and replaced with a different second removable lower portion without the removal of fasteners.

Abstract: An adapter for converting the receiver of a rifle to one which receives a cartridge housing rounds of a shorter length, said adapter comprises a body defined by four walls two of which walls defining the front and rear walls of the adapter and two of which walls defining left and right side walls of the adapter. Each of said walls defining a secondary receiver chamber sized to receive a magazine cartridge of rounds a shorter length than otherwise provided for in a rifle. The adapter includes a mechanism which cooperates with a retention catch of a rifle to effect registration of the adapter with the rifle and for allowing the magazine cartridge to be releasably connected to the adapter.