An automatic rifle bolt carrier with a fluted boss for the AR15/M16 family of firearms has been provided. The rear of the bolt carrier has been provided with a boss having bearing surfaces which are in operational contact with the interior of the host firearm's upper receiver to prevent the carrier from tilting while it is reciprocating during normal operation. The boss and rearward end of the bolt carrier are provided with flutes which allow water to flow between the buffer tube and upper receiver while the bolt carrier is reciprocating during normal operation, enabling a properly equipped firearm to be used during over the beach operations. The bolt carrier also includes a semi-circular relief cut about the top of its backmost end which is perpendicular to the axis of the bolt carrier.