Dis-assembled seems not to matter in most places.
Using the Federal definition of firearms as the example, 18 USC 921
Quote:
(a) As used in this chapter—
...
(3) The term "firearm" means
(A) any weapon (including a starter gun) which will or is designed to
or may readily be converted to expel a projectile by the action of an
explosive;
(B) the frame or receiver of any such weapon;
(C) any firearm muffler or firearm silencer; or
(D) any destructive device.
Such term does not include an antique firearm.
no mention is made of 'operability' or 'completeness'. It would appear that, generally, firearms transportation laws apply to a firearm in whatever state of mechanical assembly/disassembly it may be. Your state law may differ.