A two-piece barrel nut includes an internal nut with an externally threaded portion on one end and a plurality of engageable members on the opposite end, and an external nut with an internally threaded portion on one end that receives the externally threaded portion of the internal nut and one or more receptacles on the other end that each may receive a fastener that engages at least one of the plurality of engageable members on the internal nut to lock the external nut to the internal nut. A method for using the barrel nut to attach a barrel to a firearm is also disclosed.