I still have to adjust the size on my sugakji.. Sure it felt fine before I shot with it, and it just kills me at my thumbjoint after shooting in succession, I need to get the dremel on it again. I just don't have any guidance as to the correct fitment and I'm learning how to do all of this from book, dvd, and forum.
So I actually bought a "thumbring glove" which is made by greatree and isn't a thumbring at all, but a glove which covers the thumb, forefinger, and middle fingers, and has an extra piece of leather sewn on over the thumbpad. You guys could probably make this at home.
This works much easier, but after a session of shooting, this made my thumb pad black and blue. So I'm switching back and forth between the ring and the glove. I think the ring needs to get smoothed out even more inside, so I will try that with the dremel. If I shoot one arrow every minute or two it would be fine, and I think that is more the korean style as you shoot in a row once you are on the line.
I'm very busy so whenever I get to the range the monster in me comes out and I try to shoot a thousand arrows before I have to leave, to get in every last drop, and so, my thumb suffers. I wasn't used to it at first, as I come from a compound bow background and the release takes all the brunt of the string pinch.
I should take it easy next time and see how it goes. I'm sure it will get even better as it has already gotten a little easier than the first time I tried, my thumb itself feels more rock solid in the bent position. Just your thumbs need to get used to the pressure like anything that is a new muscle memory. I am also realizing that its not the draw that bothers me, its how much your thumb can handle! I'm thinking I could have gone down in draw weight, and still had a powerful bow after seeing what these bows can do. Just keep practicing and it should be better.