If a MA Resident with proper LTC/FID, you can buy any (legal to own) gun from a MA FFL ONLY at a MA gun show and bring it home with you.
Per Fed Law, non-MA FFLs can NOT do ANY transfers at a MA gun show. They frequently work around this by transferring it to a MA FFL who then does the paperwork with the buyer.
A MA Resident with proper license can buy any (legal to own) long gun from a FFL anywhere in the US (assuming no state laws to the contrary, MA is OK) and bring it home with them.
Private Sales are restricted by Fed Law to only those where both buyer and seller are residents of the same state.