are you a Florida resident or a Massachusetts resident?
If you are a MA resident, I would question how a Florida FFL can sell you a pistol and deliver it to you here (read PS below)
Private party.... legally you need to be a resident, but what goes on between 2 individuals privately is none of my business.
Now if you are a FL resident, in theory when you come back to MA for the summer, you need do nothing except leave the high capacity magazines here
You are not a MA resident so you have no duty to record the transaction..... but we can have a discussion on holding a MA resident LTC with a legal domicile in Florida.
If you are a MA resident you have to eFA-10 within a certain number of days of it arriving in MA, leave the seller blank fill in the rest
EDIT PS: I know there are FFL's that will take the Federal ruling of "where you lay your head at night is where you are a resident" thing, and as long as you have titles, deeds, utility bills and the like in your name with a Florida address they will sell to you and it is legal. If the SHTF in the future, just have your lawyer say you were a FL resident at the time of purchase, and legally you were. I consider myself a FL resident when I am here and a NH resident when I cross the border back into NH for such matters
It was a lot easier when you could get a Florida state issued resident ID but they stopped that a while back when thay made it illegal to have drivers licences in more than one state. One of the things it allowed you to do, in addition to buy guns, was to get the resident rates on tickets for Mousewitcz and other tourist traps. There is a deep discount for FL residents at all the theme parks, but you need a FL license or ID to get it