A gas system includes a gas block having a gas port for directing propellant gases received from a gas port of a barrel of a firearm into the gas system to cycle an auto loading feature of the firearm. A spring-loaded plunger assembly positioned within the gas block includes a plunger component having a plurality of gas ports and a plunger cap at a forward end, wherein the position of the plunger component within the gas block automatically controls an amount of gas that is allowed to enter the gas system. Mounting a suppressor to the muzzle of the barrel depresses the plunger cap and drives it linearly rearward causing the plunger component to rotate to automatically restrict the volume of propellant gases directed into the gas system through a restricted flow gas port in the plunger component.