Bring money. Understand, clearly, that there exist career individuals in the US Customs Service, and BATF who don't want another round of ammunition or a firearm brought into the US, by anyone. Always bite your tongue in dealings with these parasites, and try to forget that your tax dollars are their bread and butter. They do. Form a working relationship with a custom house broker BEFORE you have a pallet of ammunition that ships to Toronto Canada, or somewhere else, in error. You already have a lawyer, right?
That's all I can think of right now. I wish you good luck. I've been trying to work something out with a Spanish ammunition company, and simply can't get the model to work with existing exchange rates. That's BEFORE transport.
Best,
Ted
