“bringing his pistol, which was legally registered in New Hampshire...”
Weapons aren’t registered in NH.
My local police chief, who approves my CCW and has for the last couple of decades, has no idea of what I own. The long arms leave no traces at all.
But we do have family in RI, and so occasionally have to go through MA. That requires a stop in the last rest area on the freeway to disarm and disassemble. Which is insane, in that down in those holes we really need to be carrying, while up here in NH we most probably don’t.
But we stop at the first rest stop on the way home to restore our normal configuration.