Personally I'd load it into Lithunwrap, select it, then do a cylinder map on it, with ends, then tidy up the map - not really much to it.
You'd end up with both ends of the bullet at round sections with the unwrapped bullet in the middle. Get these things scaled sensibly, then go hunting for photographs in Google.
It should be easy to find brass textures, even the bullet end textures. I did this for some shotgun shells, it seriously took a couple of minutes to get it all done, and they look great.
Consider looking for brass piping, and stuff like that if you can't find decent textures for around the bullet, but really it should be all straightforward once the UV map is done.