Cold blue may or may not work if you want to return the barrel to new condition. I'm not sure you would get an even, matched finish with cold blue. Hot bluing small parts is one thing, but hot bluing a barrel yourself is a different story due to the size and the tank required for it. I've also heard good things about Craftguard and their work, and that would be my recommendation. But maybe you have a reputable local source for hot bluing?