What kind of an error is this? 1986-D Kennedy half dollar

I can assure you that this it not PMD. There is a circle indentation all the way around the inside of the rim on both sides of this coin. My photos are not great and the indentation may not show up but they are there.
Some of the letters go above the indentation. Can anyone explain how this happened? The coin is the right size and weight.

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Comments
Could be a ridge ring caused by die wear. Usually seen on copper plated cents
Search for ridge ring on:
http://www.error-ref.com
Great call
@Oldhoopster
Wayne
Kennedys are my quest...