Yes, under current NFA laws, you also (on top of having your paperwork handy) have to notify the BATFE when and where you will be traveling with your SBR if you go out of your home state, and how long you will be there.So what is the problem of traveling out of state with a SBR? Is there something more than having your paper work with you?
Bonus as a pistol vs SBR build is traveling out of State without ATF blessing.
The long and short of it... Yep...You have to ask the ATF to move property that you legally own?!?!