Provided in one aspect is an annular gas ring within or adjacent a barrel to increase the efficient transfer of pressurized gas to one or more gas ports, which may communicate the high-pressure gas to a piston to cycle the action of the firearm. Provided in another aspect are gas ports may adjacent the chamber, which may communicate pressurized gas from near the chamber to distally-extending gas tubes that communicate the pressurized gas to a distally located piston to cycle the action. A modular gas system is provided comprising a coupler that couples a barrel with a chamber and forms there-between an annular gas ring with ports that communicate pressurized gas to separate longitudinally-extending cylindrical gas tubes that feed into a gas block that supports the barrel and forms the cylinder for the piston.