Plachet weighs 2.7 grams. I understand about the 50s and acid washing coins for soda machines. Seems to me to be a real double die. I don't detect any machine doubling but lack of material not 100%. Is it a 1955 D double die? Please leave out negative comments. I really enjoy the forum Thank You.
I dont see doubling. For a year that is supposed to have very pronounced doubling I feel it should be more pronounced here. Of course the coin is so degraded you would probably have to send it in to an expert to even have a chance of finding out.
Here is a link that may help you make a judgement on your coin.http://www.lincolncentresource.com/Top50.html
What about the plachet? Its underweight, it has tapered bull nose edges and it has thousands of tiny scratches that give it a fiber look. It kind of reminds me of my 1957 D.
My best guess is that your coin was stuck in the discharge water pump of a washing machine, the dirty water going by it made it flutter and vibrate which hammered the obverse, and the reverse was exposed to the water going by at a high speed which sort of sand/water blasted it smooth. Just like rocks in a river. Some of the metal has been removed by this action, and it is smooth on the edges.