To temporarily import a firearm or ammunition into the United States, You must present the Customs and Border Patrol with:
- A valid and current Hunting License from any state, and either:
- An already approved ATF Form 6 NIA (5330.3D)
- Takes 6-8 weeks to process
- Must provide a valid Hunting License at time of submission.
- Must provide proof you are exempted (see possession above)
- Be a Canadian driving through the US as a shortcut to a destination back in Canada.
This is a basic outline. You are responsible to make sure you comply with Federal and State law.