An annular piston system for a firearm comprises a barrel, a gas block assembly, a piston, and a spring. The barrel has multiple sections lengthwise, one of the sections having at least one gas port hole to vent gas from the barrel. The gas block assembly is disposed annularly around the barrel and is adjustable to control an amount of gas flowing out of the barrel through the at least one gas port hole. The piston is disposed annularly around the barrel and can move longitudinally along the barrel in response to being pushed by the gas flowing out of the barrel. The spring is disposed annularly around the third section of the barrel and coupled to the piston. The spring limits a distance that the piston can move longitudinally along the barrel when the piston is pushed to move by the gas flowing out of the barrel.