Re: fluting barrel
It is possible, if you are using a button rifled barrel, there can be some stresses relieved that can affect accuracy, I would guess that it could happen with a cut rifled barrel as well, but might not be quite as likely. It also can be done without affecting accuracy at all. If I was going to do it after the fact, I would want to try and stress relieve it first. I think that can be done by freezing, heating, or harmonically (I don't think that is spelled properly or maybe even used properly, but it doesn't involve a harmonica)...
Dave