Rick,
Seemless mokume gane wedding bands can be made by cutting lengthwise
down a billet (that has been previously twisted, distorted and carved
into then rolled into a square cross section once more). Drill a hole
in the billet near the end and saw down the length, stopping before
you get to the end. You can then stretch this out carefully using a
punch and then your ring mandrel to get it into a circular shape. The
ends will have to be filed smooth as they will be nubs that protrude
from your otherwise circular piece.
Scott Garrison