Maybe a Dryer Coin.. Damaged by tumbling around between the drum and the wall of an industrial clothes dryer. The flaking on the edge is good evidence of that.
Hey guys just out of curiosity I weighed the nickel it came out to be 4.95/96 so I weighed about 15 others and they were all close 4 of them weighed the same as the one in picture. Plus the one in picture has a vertical line in front of his face. The other 15 were not in bad shape.
Dryer coins that have spent a lot of time tumbling tend to have the rims folded over onto the letters. Yours looks like it may have experienced a similar fate. Also, the weight tolerance for Nickels are +/-0.19gms, so there is a possibility that the starting weight was on the higher side of 5.00. You can never know for sure, but it's a possible explanation why it weighs the same as other nickels. Bottom line, there is no part of the minting or die making process that would produce a coin that looks like yours. It really doesn't matter if any of the damage explanations are correct (acid, dryer, beach), if you can't explain how it could happen at the mint, then it's very unlikely that it's an error