You would never be allowed back in the states that is if somehow you get away without jailtime. Your car would be siezed. Youd be flagged for international travel. It in essence makes you some kind of terrorist. Then the police on our side of the border may not consider you safe to own guns anymore, and come and seize them. They may even find some unsafe storage charges to hit you with as well. Now all this is worst case scenario, and Im sure people do it all the time but Im not risking it. Your friend can do what he likes but I will stay safe.