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You know how Amazon has that "Super Saver" option that promises free shipping on pretty much anything you buy if you're willing to wait, like, six weeks for it to arrive? They're not kidding. On Wednesday, The Wall Street Journal's Marketwatch set out to see just how far Amazon's commitment to free shipping would stretch. Turns out, it'll stretch pretty far.

Based on the published shipping and handing guidelines, the heaviest thing that Amazon will ship for free is the six-foot-tall Cannon Safe CO54 Commander Series Premium 90 Minute Fire Safe. It'll hold 48 guns, comes with 13 locking bolts and costs a cool $3,486.57. And if you select that "Super Saver" shipping option or paid the $79 annual membership fee for Amazon Prime, it won't cost you a penny to have it shipped to your front door. It weighs 1,509 pounds, by the way. (It's actually 1,672 pounds with all the packing materials.) Your FedEx guy, by the way, may or may not hate forever you if you order one.

If you think this sounds like a money-losing proposition, you're right. Cannon, the safe company, says that it charges $700 to ship its massive flagship safe, and considering all of the other heavy items in Amazon's inventory that qualify for "Super Saver" shipping, the costs add up for the online retailer. Amazon reported a $636 million loss on shipping costs alone last quarter, which boils down to a 1 percent loss per item. It's also no cake walk for the Amazon workers who have actually have to box this stuff up in the warehouse.