Dan,

It's been several years ago, but I have used the services of the "Cylindersmith". I don't remember the actual numbers, anymore, but I know my 629-4 MG had cylinder throats that measured less than the bore. I mainly shoot cast bullets sized to .431 or .432. I had my cylinder throats opened to .4305 (that I do remember), and get good accuracy with next to no leading at 1100 to 1200 fps.