Gun registration is regulated by state. There is no federal gun registry, yet. You have to check with your state's gun laws.
That will depend on what state you live in and the laws.
The laws on this vary by state.
Check with the laws in your state.
Depends on which laws. The US Congress is in charge of Federal laws, and the State legislature in in charge of State laws.
Loosest.
Depends on the state's firearms laws.
Research the laws of the state you are going to.
LOTS of laws. MA is not a gun-friendly state.
Maine
Depends on the law of the state you are in- laws vary state to 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.