I am wondering which is more easily done when installing a Bisley hammer into a Single Six. Is it easier to grind the hammer to the shape of the original hammer OR to open up the slot in the grip frame so it fits?
Shape the Bisley hammer to close to the original hammer shape. If you can, leave a little to "fill" or "match" the grip frame opening when the hammer is at rest position. Look at your original hammer and it will probably not quite fill up that gap. Make the Bisley a bit larger for a smoother look. It gives a clean look to the finished product.
Also, you can then return the gun to original condition should you desire.
Once all the 'heavy filing' was completed I smoothed it out with jewelers files and then various wet/dry paper and finally steel wool and cold blue.If I say so myself, unless you knew it was a 'replacement' you would never know it was not OE.