Gas operating system for an automatic firearm
Techniques and architectures are disclosed for a gas operating system for a firearm. The system includes a barrel having a bore including a rifled portion. Attached to the barrel is a gas block. Located distally of the rifled portion of the bore is a gas expansion chamber in fluid communication with the bore and the gas block. In some examples, the gas expansion chamber includes a diameter at least twice the bore diameter. The gas block of the gas operating system, in some examples, includes a piston, where in response to receiving gases from the gas expansion chamber, the piston cycles the gas operating system.
1. A gas operating system for a firearm chambered for ammunition having a projectile length of at least 0.75 inch, the system comprising:
a gas block defining a first cylinder and a second cylinder in fluid communication with the first cylinder via a gas port between the first cylinder and the second cylinder;
an insert in a distal end portion of the first cylinder, the insert defining a central projectile pathway therethrough; and
a barrel extending longitudinally and defining a bore with a bore diameter, the barrel having a distal end portion with a distal barrel end, wherein the distal end portion of the barrel is received in a proximal portion of the first cylinder with the distal barrel end positioned proximally of the gas port;
wherein the first cylinder defines a gas expansion chamber between the distal barrel end and the insert, wherein an axial distance from the distal barrel end to a proximal end of the central projectile pathway is less than 0.75 inch, and
wherein the gas expansion chamber is in fluid communication with the gas port and has a chamber diameter that is greater than the bore diameter and greater than a diameter of the central projectile pathway.
2. The gas operating system of claim 1 , wherein the insert includes a control surface surrounding the central projectile pathway, the control surface inclined with respect to the bore axis and configured to re-direct a flow of combustion gases away from the bore axis.
3. The gas operating system of claim 1 , wherein the insert is configured to reduce muzzle flash.
4. The gas operating system of claim 1 , wherein a distal end of the insert defines a distal end of the firearm.
5. The gas operating system of claim 1 , wherein the barrel has a length from 5 to 9 inches.
6. The gas operating system of claim 1 , wherein the chamber diameter is at least twice the bore diameter.
7. The gas operating system of claim 1 , wherein the axial distance is less than 0.50 inch.
8. The gas operating system of claim 7 , wherein the firearm is chambered for 5.56×45 mm ammunition.
9. The gas operating system of claim 1 , wherein the end cap is threaded into a distal end portion of the first cylinder and includes a three-prong flash hider.
10. The gas operating system of claim 1 further comprising a gas piston partially received in the second cylinder, the piston movable to initiate reloading of the firearm.
11. The gas operating system of claim 1 , wherein the gas expansion chamber has a volume of at least 0.140 cubic inches.