I've never learned to use a bo staff (or any other weapons). I remember a Kenpo Teacher telling me one time, though, that some people use a "tapered" bo for forms in competition, because they can move them faster. He told me that these tapered bos are not as strong as the "real" ones.
If I were to be taught the bo, I would prefer to always practice with a "real" one -- that is, one that would not break. You see, I would like to be able to pick up any staff and use it.
I believe that if one were to practice with a heavier bo, then one could use a lighter one easily. However, if someone practices with a light bo, perhaps they would be at a loss to use the heavier one. This adds nothing to the thread, of course, because I know nothing about the staff. I appreciate the comments regarding which bo to use (a "log"! --> hahahaha! that was a good one! --> I can imagine someone trying to use a telephone pole!)
