Looks like the coin has been damaged to me. A large smooth edge is AC sign that’s it been hit repeatedly with a spoon to make it a ring.
Are you using a gram scale or a kitchen scale? You Dime has an altered edge. That did not occur during the minting process. It's not a mint error of any kind.
Your coin looks like it has a bezel on it. When a coin is spooned the writing on the edge of the coin rolls up and is still visable on the inside edge. On your coin half the words have disappeared, like they have been covered up.
Interesting. But the OP stated that is weighs less than a normal Dime. Wouldn't a Bezel make it heavier?
A person would logicly think so, but my observation is from a visual stand point only. The outer edge also seems to have a brassy color to it. Photos can be deceiving, that is why I used the word looks like.
An error happens at the mint. This is an important distinction to remember. What part of the minting process caused this? This is PMD post mint damage most likely caused by spooning as previously demonstrated. Although it's possible it was damaged another way.
