I received the factory letter today for my Model 66-1 that I posted about earlier. It was an odd configuration in that it has a 4" barrel and a round butt. In my previous post, all comments eluded to the fact that the barrel or the grip having been changed at some time in it's life. The factory letter states that the gun left the factory with a 4" barrel and a round butt and that an error was possibly made in recording the serial number as a square butt. Is there a digit in the serial number that indicates square butt vs. round butt? From what the letter is stating, I take it that the 4" round butt does exist.