[Rupert]

Note that if they only mount the weapon when outside the US, the FAA has no jurisdiction anyway. On the other hand, if they fly round international waters so armed, and then go and annoy some FAA (or other law enforcement) official, they might find themselves labelled 'pirates' and locked up. Getting permission to have guns mounted in the Antilles in general will be a nightmare, given how many different countries' hold territory there.