Abstract: An aftermarket handguard system is described for use with an assault rifle, such as an AR-15. The system includes an elongated arcuate upper handguard section substantially defining a longitudinal axis and a plurality of radial planes normal thereto. The handguard section has left and right generally outward directed rail flanges having non-parallel flange mating surfaces. Two lower arcuate handguard sections are provided also each having laterally extending rail flanges with non-parallel flange mating surfaces. Three “T” shaped accessory rails each having a dovetail shaped portion are provided for mating to the non-parallel flange mating surfaces. Accessories may be mounted on the accessory rails in the conventional manner.