Not needed in most States.M/L are not considered firearms.
I go to a Rendezvous in Wash. State, I declare my firearms to the U.S.border out of respect,I,ve had one Customs officer ask to see my registrations,probably out of curiosity more than anything.Normally they wave you through.
Yiu can also buy a BP firearm in the same States without an FFL ,of course you have to go through the proper channels coming back,unless it's a Flinter, then just declare and pay the taxes.
I might still have a letter from the BATF outlining this info.I'll have a look this evening.
Cheers nessy.