A breech assembly for an automatic weapon having a barrel extension aligned with and extending outwardly from the rifle bore. The barrel extension has a throughbore aligned with the rifle bore and a non-circular locking recess at a rear end of fee barrel extension. The barrel extension also includes an internal thread in the throughbore. An elongated bolt includes an external thread complementary to the infernal thread hi the barrel extension. The bolt is mounted to a bolt carrier that is longitudinally slidably mounted to the gun body. Longitudinal movement of the bolt carrier simultaneously longitudinally and rotatably drives the bolt so that the bolt thread is threaded into the barrel extension.

A reciprocally-cycled weapon delinks and fires cartridges in open-end linked ammunition belts or close-end linked ammunition belts. The weapon has first round select and first cycle fire capabilities. The bolt carrier assembly translates out of phase with the extractor assembly. The extractor assembly is configured for rearward extraction of the cartridges in close-end linked ammunition belts. The weapon works seamlessly with open-end linked and close-end linked ammunition belts.

A reciprocally-cycled weapon delinks and fires cartridges in open-end linked ammunition belts or close-end linked ammunition belts. The weapon has first round select and first cycle fire capabilities. The bolt carrier assembly translates out of phase with the extractor assembly. The extractor assembly is configured for rearward extraction of the cartridges in close-end linked ammunition belts. The weapon works seamlessly with open-end linked and close-end linked ammunition belts.

A bolt for a firearm includes, among other things, a bolt body extending between a first bolt end and a second bolt end, the bolt body defining a shaped cavity adjacent to a breech lock recess. The shaped cavity is defined by a cavity floor extending between a forward cavity face and a rear cavity face, the forward cavity face defines a forward angle relative to the cavity floor, the rear cavity face defines a rear angle relative to the cavity floor, and each of the forward angle and the rear angle is acute. A bolt assembly for a firearm and a method of fabricating a bolt for a firearm are also disclosed.

A bolt for a firearm includes, among other things, a bolt body extending between a first bolt end and a second bolt end, the bolt body defining a shaped cavity adjacent to a breech lock recess. The shaped cavity is defined by a cavity floor extending between a forward cavity face and a rear cavity face, the forward cavity face defines a forward angle relative to the cavity floor, the rear cavity face defines a rear angle relative to the cavity floor, and each of the forward angle and the rear angle is acute. A bolt assembly for a firearm and a method of fabricating a bolt for a firearm are also disclosed.

An ammunition magazine is used with a reciprocally-cycled weapon for delinking and firing cartridges in close-end linked ammunition belts. The magazine includes a housing with an ammunition indexing mechanism fixed to one side of the housing. A magazine feed box is disposed above the ammunition indexing mechanism. The magazine feed box includes a movable follower having an upper and a lower position and cam pins that engage cam slots in the magazine feed box. The movable follower is configured to receive a cartridge from the weapon.

An externally-operated weapon has a direct current servo motor that provides motive force to drive the weapon operating group at an average rate of fire. Within a single cycle, the weapon operating group is driven at rates greater than and less than the average rate of fire, while the overall rate for a single cycle is maintained at the average rate of fire. Some benefits of servo motor control include reduced power consumption, increased bolt dwell time, expansion of the weapon's battlefield role from one to many roles, and increased accuracy and shot-to-shot precision while firing from an open bolt position.

A firearm can have a bolt having a plurality of locking lugs that are configured to have a shear area that is larger than that of a standard M16/M4. A bolt carrier can have a bolt that has a double cut cam having an unlocking cam surface that has sufficient dwell increase to delay a start of unlocking when the bolt carrier is used in an M4 carbine. A stepped extractor pin may be provided that prevents disengagement of the extractor pin. A tube can be configured to provide gas from a barrel of the firearm to the piston via the carrier key. The tube can have a heat radiator formed from triangular shaped threads on at least a portion of the tube. A piston on the bolt and can have a plurality of rings including pairs of mating rings that are formed and maintained as a matched pair.

Firearms with bolt mechanisms, ambidextrous functionality, and/or isolated receivers are disclosed herein. A multi-caliber ambidextrous firearm can have a receiver and a bolt mechanism with a bolt that seats against one or more load bearing surfaces of the receiver. The load bearing surfaces can be configured to maintain proper contact before, during, and/or after a firing event. A bolt head of the bolt mechanism can be replaced to use the bolt mechanism with different cartridges.

A rifle has a receiver, a cartridge chamber connected to the receiver, and a bolt slideable longitudinally in the receiver, the bolt is engageable with a cartridge in the chamber. A bolt carrier is slideable longitudinally in the receiver to move the bolt into and out of engagement with a cartridge in the cartridge chamber, and a bolt handle is connected to the bolt carrier. The bolt handle is positionable in a manual position extending from one side of the rifle to permit manual firing of the rifle and in a semiautomatic position about 180 degrees different from the manual position and extending from the other side of the rifle to permit semiautomatic firing of the rifle. The position of the bolt carrier may be changed between the manual and semiautomatic positions without removing the bolt carrier from the rifle.