Obligatory not a lawyer statement. Here is a link to a lawyer's page discussing possession of a firearm in MA. https://criminal.altmanllp.com/gun-charges-weapons.html
Basically, you need a LTC to possess a firearm in this state. For CYA purposes, the way I would do it would be to have a resident with a LTC take possession of the firearms for you and send the mags to a Fed Ex holding in the free state of NH.