An adjustable gas system for a firearm includes a gas block, a gas regulator and a plunger. The gas block is configured to be fixed to a barrel of the firearm, and includes a hole configured to receive a gas tube of the firearm. The gas regulator is configured to rotate around the barrel, and includes a plurality of gas port holes of different sizes. The plunger is configured to hold the gas regulator at one of a plurality of angles with respect to the gas block such that a select one of the plurality of gas port holes is aligned with the hole on the gas block to allow a respective amount of gas to flow from the barrel to the gas tube through the select one of the plurality of gas port holes.