Not a lawyer so here goes.
If said antique is a certifiable as one then you do not according to the law…
http://www.mass.gov/legis/laws/mgl/140-121.htm
The provisions of sections 122 to 129D, inclusive, and sections 131, 131A, 131B and 131E shall not apply to:
(A) any firearm, rifle or shotgun manufactured in or prior to the year 1899;
(B) any replica of any firearm, rifle or shotgun described in clause (A) if such replica: (i) is not designed or redesigned for using rimfire or conventional centerfire fixed ammunition; or (ii) uses rimfire or conventional centerfire fixed ammunition which is no longer manufactured in the United States and which is not readily available in the ordinary channels of commercial trade; and
(C) manufacturers or wholesalers of firearms, rifles, shotguns or machine guns.
Though I can not find where it states in the law that you must “register the transfer of ownership” of a long gun when brought in from out of state.
If you are a member of GOAL call and leave a message for Nancy or email her, if you are not then call talk with Nancy, join then ask her.