sometimes the ring will vary in thickness making it difficult,, just keep trying,
Im pretty good at it,, been doing it about 30 years,,,, but sometimes I hit a stave that almost seems impossible,, I just slow down and do the best I can,,
keep in mind,, if you are pretty close,, and only have a bit of violation,, a rawhide back can make it a shooter,, so there is hope,,
I am working on one now, the rings were so thin I have a spot I dont like,, so I am gonna rawhide back a proceed,,,,, you need to know how to do that anyway,,
also some close ups of where your at,, would help