Button rifled barrels are contoured after the button has been pulled through the bore so I'm not sure there's anything inherently wrong with recontouring, I don't really see the difference between the initial contouring and taking a little more off after the fact. I'd bet most smiths don't do it because most aren't set up to do it properly, and they don't really need to be since you can get most any contour from the barrel maker. That being said, I don't think I'd waste the money recontouring a factory hammer forged barrel. I'd be more worried about a hammer forged barrel moving under the recontouring than a quality button or cut rifled barrel. By the time you paid for the smith to pull the barrel, recontour it, reinstall it and refinish it you'd be most of the way towards paying for a decent custom barrel.
