Re: Turning and/or fluting an existing barrel?
I've been told profiling an already finished barrel can be a crap shoot...might not effect it, or might. Profiling, or lathe turning, can introduce stresses into the barrel that it won't normally experience and there's a good chance the barrel will react to those stresses, and not in a good way. Fluting is less of a risk since it's done lengthwise and really doesn't introduce any unusual stress, although it may relieve some which could effect accuracy.
HTH