As crude as it seems, I have used a hacksaw and a triangle shaped file, with one side made safe (file teeth ground smooth). After deciding on the position of the front and rear sights, measure the sight base. I will then cut a series of notches across the barrel, being careful against cutting too deep. Only deep enough for the sight base to fit flush with the barrel. Then working slowly with the file, smooth the slits to sight depth. Then work on filing the angles for the dovetail angle. Work it for a tight fit between the sight and the barrel. Check the fit, file a little bit, then check the fit again and repeat until you are satisfied.