Gasoperated

Gas-operated refers to a method of cycling a firearm’s action by using a portion of the high-pressure gas produced when a cartridge is fired. A portion of the gas is directed from a gas port in the barrel into a cylinder or directly onto the action, where it powers a moving component that unlocks the action, extracts the spent cartridge, chambers a new round, and resets the mechanism for the next shot. The exact arrangement determines how the gas pressure is used to operate the firearm.

There are two broad families of gas-operated designs. In direct impingement systems, the gas is routed directly onto the bolt carrier or another moving part, which uses the gas pressure to drive the action without a separate piston. In gas-piston designs, the gas first acts on a small piston, which then transmits force to the bolt carrier or locking mechanism via a connecting rod or link. Gas-piston systems are commonly categorized by the length of the piston stroke: long-stroke designs use a piston that travels a longer distance, while short-stroke designs rely on a smaller piston that imparts the motion with less travel. Each arrangement has trade-offs in reliability, heat management, weight, and maintenance.

Advantages of gas operation include the ability to cycle the action under diverse conditions and with various ammunition, and the potential for cleaner rotary or piston-driven mechanisms that separate exhaust from the receiver. Disadvantages can include fouling in direct impingement systems, added weight and complexity in piston systems, and sensitivity to gas port timing and cartridge pressure. Gas-operated firearms have been widely adopted in military rifles and light machine guns since the mid-20th century, evolving with variations in gas port sizing, piston design, and system length to suit different platforms and calibers.