What is a Machine Gun?

Section 479.11 of the NFA defines a Machine gun as. Any weapon which shoots, is designed to shoot, or can be readily restored to shoot, automatically more than one shot, without manual reloading, by a single function of the trigger. The term shall also include the frame or receiver of any such weapon, any part designed and intended solely and exclusively, or combination of parts designed and intended, for use in converting a weapon into a machine gun, and any combination of parts from which a machine gun can be assembled if such parts are in the possession or under the control of a person.

Is a fully automatic 6mm air soft gun a machine gun under the NFA? Of all the terms defined in the NFA, one of the most frequently used ones is the term weapon which is not defined.  I have submitted this question to the ATF and will update the site when we obtain an answer.