Therefore, even in pieces, it is still a firearm.(29) The term "handgun" means—(A) a firearm which has a short stock and is designed to be held and fired by the use of a single hand; and
(B) any combination of parts from which a firearm described in subparagraph (A) can be assembled.
The term "firearm" is defined in section 921(a)(3) to include any weapon which will or is designed to or may be readily converted to
expel a projectile by the action of an explosive; the frame or receiver of such weapon; any firearm silencer; and any destructive device..
A nonlicensee may ship a firearm by a common or contract carrier to a resident of his or her own State or to a licensee in any State. A common or contract carrier must be used to ship a handgun. In addition, Federal law requires that the carrier be notified that the shipment contains a firearm and prohibits common or contract carriers from requiring or causing any label to be placed on any package indicating that it contains a firearm.
[18 U.S.C. 922(a)(2)(A), 922(a) (3), 922(a)(5) and 922(e), 27 CFR 478.31 and 478.30]