Abstract: This Regulated Bolt Carrier is a lightweight carrier having a built-in gas regulating gate. As a drop-in assembly it enables tuning of the gas system used in firearms of the AR-15 class. Adjustments of a continuously variable nature may be made quickly through the port door without requiring disassembly of the firearm. A gas “regulator gate” located under the gas key below a gas port inside the body of the bolt carrier itself is cut as a half-moon. Rotating the regulator gate on its axis changes the position of the half-moon cutout, blocking the entry of gas into the system. The regulator gate can be set anywhere from fully open to fully closed and is held in position by a small lock screw. For maintenance, the gas regulator gate can be pushed out of its bore via an access hole on the opposite side of the bolt carrier.