It's also worthwhile to note how the BATF interprets the law, per their FAQ.
Maybe it won't hold up in court, but it seems unwise to ignore their plain statement of how they believe it reads and also the implication that they intend to attempt to enforce it per their interpretation.
It seems likely that the money spent to ship it per the contract carrier's policy could save the shipper a lot of money, time and trouble in the (admittedly unlikely) event that the package breaks open or the contents are otherwise discovered in transit.
Maybe it won't hold up in court, but it seems unwise to ignore their plain statement of how they believe it reads and also the implication that they intend to attempt to enforce it per their interpretation.
It seems likely that the money spent to ship it per the contract carrier's policy could save the shipper a lot of money, time and trouble in the (admittedly unlikely) event that the package breaks open or the contents are otherwise discovered in transit.