Bronze cannons can be a brownish-green color in saltwater. On land it ranges from a white, talc yellow or light green oxidation that brushes off easily.
God told Moses to throw the staff, and God turned it into bronze and it was known to be the Nehushtan staff. When this happened, the staff turned into a snake. God ordered Moses to pick up the staff...
The bronze bow is not an actual bow in that book. It is a symbol of strength that the group bases itself on. They believe that with the strength of the Lord, they would be able to even bend bows made...