That's a viable explanation, however my issue with it is the weight is exactly the same (not close, but spot on) with normal halves and all of the lines, including the D mint mark are all clear and sharp (under magnifying glass, picture doesnt do it justice). I dont think an "exchange of copper" process would still keep the lines as sharp as they appear while not changing the weight after loosing 8% of its material content. I thought through what you've said before I posted but it doesn't pass to me as a severely weathered coin.