Abstract: A gas regulator block can be configured to mount to a barrel of a firearm. A gas regulator can be disposed substantially within the gas regulator block and can be configured to adjustably vary an amount of gas flow through the gas regulator block. A cover configured to cover a portion of the gas regulator block to inhibit inadvertent adjustment of the amount of gas flow and configured to uncover the portion of the gas regulator block to facilitate intentional adjustment of the amount of gas flow. A gas passage can be formed in the gas regulator block in a forward location and the gas port can be configured to communicate gas from the barrel to the gas regulator.