In Ireland milkchurn is a weapon if it is stuffed with gravel and scrap iron and PE, empty it is still just a milkchurn.
My POMZ grenade is a nasty anti-personnel weapon but with the charge and det left in a desert 4000 miles away it is just a souveneir. So thought the customs man at LHR anyway.
Lets apply a bit of common sense to this, a RPG tube is little more than a picturesque drainpipe, and given the relative unavailability of RPG rounds in the US (as opposed to plastic, scrap iron and gravel) just about as dangerous.