Gas-operated firearms use the gas produced from firing a round to cycle the action of the firearm. When a bullet is fired, some of the gas from the burning gunpowder is redirected through a port in the barrel. This gas then pushes a piston or operates a mechanism that ejects the spent cartridge and chambers a new round. This system allows for semi-automatic or automatic firing, as the firearm can reload itself after each shot. Common examples of gas-operated firearms include AR-15 rifles and M16 rifles, which are widely used in both military and civilian contexts.