Wrong. If you have the complete "combination of parts" to convert then you have a machinegun, even with nothing else.
27 C.F.R § 479.11
Machine gun. 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.
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For example, all the parts to convert an AR-15 to an M-16 configuration, or all the parts to convert an M-1 carbine to M-2 configuration.