I found a kind of cool study that looked at traces of metal in the mandibles of the cigar beetles. No mention of them chewing THROUGH metal though. I only skimmed it so someone with more time can look but doing a search for the word metal popped up alot of info on traces in their mandibles.
http://ddr.nal.usda.gov/bitstream/10...ND23316635.pdf
Edit:
This article suggests that they cannot eat through metal. (I am not saying the above does, I am just throwing some more articles and research out).
Quote:
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Store susceptible foods in insect-proof containers of glass, heavy plastic, or metal, ideally with screw-type lids, or store in a refrigerator or freezer. Use older packages before new ones, avoid spillage in cabinets, and always keep food-storage spaces clean. Properly ventilate the storage area to discourage these moisture-loving pests.
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http://ohioline.osu.edu/hyg-fact/2000/2083.html