BVS, I've done a couple of walnut bows where I chased a ring and got both sapwood and heartwood in the limbs. They both worked well. It is very difficult to chase a ring in walnut but doable with a little water and good light. The ones I did had moon rings. It's not too bad to get a yearly ring but yeoon rings give a little trouble. Both of mine had many small violations in the sapwood but has held fine. And a couple tips wth walnut, make if fairly wide, it bends easy with steam and it takes heat treating very well.
Kyle