Gas-operated firearms use the energy from the gas produced when a round is fired to cycle the action of the firearm. This mechanism allows for semi-automatic or automatic firing, as the gas is redirected to operate the bolt or slide, ejecting the spent cartridge and chambering a new round. Common examples of gas-operated firearms include the AR-15 and AK-47. These firearms are popular in military and civilian applications due to their reliability and efficiency. The gas system can vary, with some designs using direct impingement while others utilize a piston system to manage the gas flow.