Adjustable gas valve for a firearm

A firearm barrel assembly comprising:

• a barrel defining a bore extending along a bore axis and a barrel port extending transversely from the bore to an outside of the barrel;
• a gas block secured to the barrel, the gas block defining a gas passage in communication with the barrel port and a valve opening in fluid communication with the gas passage;
• and
• a valve body sealingly received in the valve opening, the valve body defining an outlet port, a first valve opening of a first size, and a second valve opening of a second size different from the second size, wherein the first valve opening and the second valve opening fluidly communicate with the outlet port;
• wherein the valve body is movable by hand between a first position in which the first valve opening is aligned with the gas passage and a second position in which the second valve opening is aligned with the gas passage.