Eldo,
First of all, you could not have gotten better advice on how to do it by hand than that given by Dave Person and others above.
However, you did not mention how much experience you have with filing metal flat by hand and draw filing. If you have never done it before, or don't have much experience, I would most strongly suggest getting the experience first and before you go to work on a barrel.
When I was an Instructor, I taught apprentices the "Art and Mystery of Zen Hand and Draw Filing" by first using scrap pieces of steel and that is still the best way to learn it. Oh, that was just a catchy way to describe it, that seemed to open them up on how to do it. :haha:
Gus