Massad Ayoob has stated that every single case of a NFA weapon being used has gone to a Grand Jury at a minimum. How much money do you have set aside for legal defense funds?
Both of the cases that he knows about, yes. In one case it was as simple as "ok, you're good." and the victim went home to patch up (the Beckwith incident)
One important note - NFA owners have gone above/beyond to get background checks and such to own them. A competent lawyer will work that in favorably.