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When I was going hard at it I would weigh the boxes before I open them and you can calculate almost exactly how many are copper in there. Often you will get skunked with a box of all new pennies, some of those boxes are from the mint though and I found I could sell those online at a slight premium so I could dispose of them.

HARDCORE, man... you are HardCore!
Yes that is an easy calculation, weight vs. a known quantity. My bank lets me by their 're-rolls' so I do not get mint rolls. I specifically ask for those. Never got a single mint roll!

don't get me started on how many pennies you can move with a leased Nissan Altima. There is not a bad resale market for actual mint boxes, sometimes you get boxes that are almost all zinc but they are not mint. those clear plastic rolls that have like one or two old pennies mixed in are worthless.