An assembly for directing propellant gas to an action of a firearm includes a barrel and a gas block. The barrel has a plurality of gas ports that communicate with the bore of the barrel. The barrel and the gas block define a passage that receives pressurized propellant gas from the bore by way of the barrel gas ports, and directs the propellant gas to a gas port of the gas block. The plurality of barrel gas ports and the passage act as a manifold in which the propellant gas is taken from multiple locations within the barrel, combined into a single flow, and directed into the gas block via the gas block gas port. The pressurized gas is then routed to an action of the firearm by way of a gas tube and a gas key.