It's my opinion that if the barrel is pitted enough that the rifling is screwed up then that barrel, in that caliber, is pretty well shot. By that I mean if it's pitted, that means there's less metal and small pits or holes in the rifling (lands & grooves). You can't put that metal back. The only way to salvage that barrel (severely pitted) to like new shape is to reline it. It would generally be cheaper to replace the barrel than it would be to reline or rebore/rerifle it. If the pitting is very light it MAY shoot ok just the way it is (with a little cleanup). In almost every instance I've seen, the new barrel will outshoot the old pitted 1 anyway so why bother unless you're restoring it.