Based on that, then I'd say it is probably not a compression ring. I've never seen one that did not taper to a sharp edge. Plus, they would shine brass all around.
You probably have one of the finger rings.
This is off topic, but in the Larmie, Wyoming (university) museum, they have a guy (cowboy?) that was (they surmise) shot in the hip so he fell to his knees; he was then shot through the head. .44 or .45. Then he was buried. This was back in the 1800s. When they dug him up, they found a black rubber type ring on his wedding ring finger. The description said it was a widowers ring. Apparently, in the old days, if you lost your spouse, you'd wear a black rubber wedding band.
He had a wide brimmed black hat and was well dressed. He was delicate boned, so the figured English, and he was very tall for the time (6' plus).
You look at and read stuff like that and your head just starts spinning with "who, what, where, how, why and when . . .????" I saw that 30 years ago and I still think about him.