Verification all the way from the Supreme Court of the United States:
U.S. v. Thompson/Center Arms Co., 112 S.Ct. 2102, (U.S., Jun 08, 1992)
"Respondent Thompson/Center Arms Company manufactures a single- shot pistol called the "Contender," designed so that its handle and barrel can be removed from its "receiver," the metal frame housing the trigger, hammer, and firing mechanism"
("The kit Thompson/Center Arms manufactured for converting the Contender into a rifle contained a twenty-*876 one-inch rifle barrel, a rifle stock, and a wooden fore-end. Id. Assembling these three parts with the Contender's receiver would result in a carbine rifle with a twenty-one inch rifle barrel, which, like the pistol itself, would not be a "firearm" for purposes of the NFA. Id. at 507-08, 112 S.Ct. 2102. However, by using the ten-inch pistol barrel from the Contender instead of the twenty-one-inch rifle barrel from the parts kit, a short-barreled rifle--a "firearm" under 26 U.S.C. § 5845(a)(3)--could be assembled. Id." From US v. KENT, 175 F.3d 870 (1999) discussing US v. T/C)
"the fact that the unregulated Contender pistol can be converted not only into a short-barreled rifle, which is a regulated firearm, but also into a long-barreled rifle, which is not. The packaging of pistol and kit has an obvious utility for those who want both a pistol and a regular rifle, and the question is whether the mere possibility of their use to assemble a regulated firearm is enough to place their combined packaging within the scope of "making" one. "
"Accordingly, we conclude that the Contender pistol and carbine kit when packaged together by Thompson/Center have not been "made" into a short-barreled rifle for purposes of the NFA."
The Supreme Court may not always be right, but they are final.
Cheers, Otto