Dix has very good advice. I always hand-ream my long beads. The tapered long diamond bits will widen the holes at each end and the untapered ones will build up pressure from within and can break the bead. I've broken a few long beads using a straight diamond reamer in my Dremel. The chips the diamond reamer creates at the bead hole are very unsightly and hard to smooth down.
Edited to say: It gets much easier and faster with practice. I can now clean my long beads faster by hand than I could with the Dremel
