Certain Magazines have gotten through with the exception of ones with the dummy bullets inside. But I think it depends how the people at customs feel that day.

I've gotten a bunch through. Though once they assessed a box of AK mags (Mag brand) as being 500 dollars, I had to pay a &%@*load of import fees at the time and then fill out forms to get the money back. I have even had luck getting in p90 mags, I realized that customs generally won't open padded envelopes so I just order them one at a time. I save about 50% so even in half of them get confiscated (I am 3 for 3 success rate so far. ) I am fine. The only thing that sucks is the time to get them all.