I would say Vermont, but I'm not 100% sure.
I know you don't need a permit to carry a concealed pistol, or to buy or own a pistol, rifle, or shotgun.
Per federal law, you have to be 18 to buy a rifle, 21 to buy a pistol, and you have to pass a background check.
Gun registration is regulated by state. There is no federal gun registry, yet. You have to check with your state's gun laws.
Loosest.
Depends on which laws. The US Congress is in charge of Federal laws, and the State legislature in in charge of State laws.
That will depend on what state you live in and the laws.
Check with the laws in your state.
The laws on this vary by state.
Research the laws of the state you are going to.
Depends on the state's firearms laws.
LOTS of laws. MA is not a gun-friendly state.
The first layer is federal gun laws. From there State laws can restrict gun laws more, but not make them more liberal. From there County laws/ordinances can restrict more so, but not make them more liberal. <><><> Above is correct, but with an exception- Many states have enacted "preemption" statutes, to prevent a "patchwork quilt" of gun laws that vary dramatically city to city, county to county. In those states, the State Legislature preempts the ability of a county to pass gun laws, reserving that right to itself.
Depends on the law of the state you are in- laws vary state to state.
Maine