Being able to duplicate a metallic look on any material is all about how much time and effort you put into finishing your surface.
Like Knives said, your biggest goal is to seal and hide the grain of the wood, the main thing people think of with metal is its characteristic to reflect light. If you can see grain on your surface, it means that the surface isn't smooth enough to properly reflect light and it will hurt the overall effect.
There's tons of ways to go about this, sanding sealer, coating the surface in resin, varnish, clear coats, gesso, filler primer, ect. Really just depends on which you want to go with.
Once your grain is sealed you get to sand the surface smooth. The higher grit you sand to the better it will look. For things like sword blades I'd say wet sanding up to at least 600 grit is advisable, depending on how much wear and damage you want to incorporate. Since you didn't provide a reference picture for the bow its up to you to judge how smooth and clean you need the finish to be.
Rub n' Buff is a great option for metallic finishes, just remember that it either needs a clear coat to seal it, or a very long time to dry after application. Otherwise it has a tendency to rub off. Testor's Metalizer is another buffable paint option if you have access to an airbrush.
Dry brushing highlights and lowlights is also another way to get a very convincing metal look especially if you're going for the worn look.