He did the right thing!
Richard Hamblen built machine guns for the Tennessee State Guard after the 9/11 attacks,
details on the case can be found here
His intent was not to have a machine gun, but to protect his men, his unit, and his country in a time of duress, he should be rewarded for his efforts, not prosecuted.
Many of the founders of this country put together arensals of cannon, shot, and powder to protect the colonies prior to the revolution, I don't see that this case is all that much different