Demonwolf the square in a guns hammer casting is not made with a conventional modern broach which cuts the hole be it square round or oblong. The method is a little more brutal and makes more sense when you hear the explanation I was given when I first wanted to fit new replacement hammers to a gun. Contrary to what we may think the square hole in the hammer boss on old Brit guns is slightly tapered from the back to the front of the hammer, and is actually swaged into a tapered square from a round hole drilled in the boss starting from the back in the correct orientation to enable the hammer to sit in its correct position. So lets get the complications of hammer fitting in proportion they were fitted by hand by a normal man and the method used has worked perfectly for hundreds of years and it is not rocket science.
Firstly you need to make a smooth square tapered punch (can also be called a broach) that must be harder than the hammers metal so you will need to purchase some round silver steel which is heat treatable steel (US they call it drill rod) cost of about 3. Having obtained the silver steel you will have to file it to a square about 40mm long (1 inches approx.) tapering between about 2 to 4 degrees having the hammer mounting square size about three quarters the way along the punch from its smallest dimension then harden and temper it (this is not hard to do look on u tube). Contrary to what we may think the square mounting hole in a hammer on old Brit guns and others is slightly tapered and the reason for it is that because of the taper as you tighten the hammer retaining screw the mounting square is forced to the point that it is tight in the hammer hole, and should it work loose with use you re-tighten the retaining screw to move the hammer slightly on the taper and so tighten.
Its use is simple you drill a hole in the hammer boss slightly smaller than the hammer mounting square and introduce the punch starting from the back of the hammer boss making sure that the square you are making is in the correct orientation for the correct hammer position. Hammer the punch into the hole while supporting he hammer on a metal surface with a hole that will clear the punch as it moves through, this will compact the metal improving its density and of course shape the hole, as you move the metal with the punch you can try the hammers fit on its mounting square. Sometimes you may have to adjust the size of the hole by using a file to remove some metal to help things along but it should be more hammer than file.
I hope this all makes some sense. damascus
