Whatever you do, just make sure to have an all in one lube (like CLP) or some type of oil. You want to oil your bolt immediately so it doesn't rust. From there you can polish it to prepare it for bluing or prep it to use something like DuraCoat SL (SL meaning Self Lubricating, which is what I will probably use when I get around to trying this project). You could also have it parkerized, which would be the best option if you just want a flat black look with good rust protection. They sell kits to do it at home if you're up to that kind of thing.