Eightbore:
I thought between my and L Browns posts we'd explained exactly how to legally do this. There's no way you can just carry it back. The way to get it back hassle free, and this is assuming it's a shotgun*, is have it run from the British dealer to an American dealer each of whom who will accept it and prepare the proper paperwork. It shouldn't be all that expensive it just takes patience and time.
* If what you are attempting to import is preceived as some sort of military firearm then all the rules change.
Jim

The 2nd Amendment IS an unalienable right.