I regulate the back sight on Colt style revolvers by wrapping the revolver in several shop rags, then clamp it loosely in the bench vice.
Then, I firmly brace my wrist on the jaws of the vice, and use a Dremel tool with a cut-off wheel to cut straight down in the center of the "V" notch. (a very thin file would work too)
Easy does it, and load a chamber and try a shot after each small increment of added depth.
When you get the impact down where you want it, carefully widen the first cut to the perferred width. However, before widening the cut, shoot the revolver enough to determine if it is hitting to one side of the line of sight, and if it does, widen your initial cut in the opposite direction to move the impact to point of aim.
For instance, after making the first narrow cut to a depth that brings the impact is down to point of aim, but hitting to the right of point of aim, widen the cut on the left side. The impact will then move to the left, and line up with the point of aim.
As long as care is taken to keep the wheel from grabbing and kicking out of the cut (keep your hands well braced on something solid), the alteration of the notch is hardly noticeable.
