Supposition:
You have a "Primary" residence in Massachusetts and a resident LTC
You have a Winter Home in Florida
You have a hunting camp in Pennsylvania.
You buy a rifle in Florida with the intent to deliver it to your hunting camp.
You fly to Massachusetts from Florida with your rifle, spend the night at your home in Massachusetts, then drive to Pennsylvania.
I would not think you would be required to register the rifle and it is not in Massachusetts for more than transitory purposes.
Similarly, if you have primary residence in Mass, but a Summer home in RI and purchased a shotgun in RI, and brought it to Duck hunting camp in Maine, would you be expected to register the shotgun in Mass as you drove through Mass to get to Maine?