If one of the landmark decisions regarding the second amendment was based on the inapropriateness of the weapon in question (short barreled shotgun) as a military firearm, there should be no question of the appropriateness of a machine gun, captured or otherwise.
Even under that lame decision, the Second Amendment should apply, and sans infringement, there should be no registration.
As for veterans, we trusted these individuals with tanks, warplanes, combat ships, even nuclear weapons. What? we can't trust them with a rifle when they get home? If anyone has earned the right, they have.
Or is registration simply a precursor to rounding up the weapons in question? As for demilling the weapons, phooey! It is already legal to own a demilled machine gun. It is a display piece only, incapable of firing or being made to fire. (Useless sculpture.)
Just repeal the NFA and let these guys keep their stuff.
"These types of firearms, accessories, and ammunition (machine guns) are precisely those most suitable for military and militia use. and have been so issued by the Federal government to U.S. armed forces. The Court held that the keeping and bearing of such firearms was explicitly protected by the Second Amendment."
It is unconstitutional to "...infringe..." on the "...right to keep and bear arms..." by preventing military weapons from being owned by citizens, as stated in U.S. v Miller.