A modular fore-end rail assembly for mounting onto a firearm includes an upper hand guard, a lower hand guard and a clamping member that combines with the rear portion of the upper hand guard to encircle and clamp onto the barrel nut thereby supporting the entire assembly from the front of the upper receiver and preventing any transfer of load into the barrel. The lower portion of the hand guard is slidably received into channels formed in the upper hand guard and is retained in its installed position by a spring biased detent located in the clamping member. The lower hand guard is removable by simply depressing the detent and sliding the lower hand guard forward. By providing for the easy removal of the lower hand guard, other auxiliary devices may be mounted to the upper hand guard.