Here's a really OLD thread covering the same subject... and let it be known that I haven't a clue about the OP's coin. http://www.cointalk.com/t38394/
This is a tuff one. We need pictures of the edge. It could be someone was bored and filled one down or it could be a true error.
I would have to say this is a real error coin. the reason I say this is the fact that it would be nearly impossible for anyone to duplicate this coin. look at how the letters in LIBERTY are stretched outward toward the edge of the coin and not complete. this is because the nickel planchet was not retained by the collar and the metal flowed outwards instead of filling in the letters of the die. This is a extremely valuable coin if it is genuine and I'm about 100% sure it is. EDIT: I looked at the coin that was on ebay and it looked fake to me. a real nickel struck by half dollar dies should look like the op's coin in this thread.
Wow-zers! Certainly looks like a genuine off-metal error to me, along with, what looks like, a reverse that has been struck-through a die-scrubbing cloth (As Mike has already pointed-out). What leads me to believe it's genuine? - Notice the stress of metal on the obverse lettering (what remains of "LIBERTY"). This is typical of related errors, and, as one may assume, it is nearly impossible to replicate artificially. May I ask, OP - What leads you to believe this may not be a genuine mint error? -Brian
