The 4" was a special order gun after WWll until around 1980, when Smith standardized barrel lengths to 4, 6 and 8 3/8 inches. The 27-2 was only made for a year or so until the change to the 27-3 which eliminated the pinned barrel and recessed cylinder chambers. I have never even laid eyes on a 4" barrel 27. There are reports that there are some 27-2s with non pinned barrels and recessed cylinders, as well as some with pinned barrels and non recessed cylinders. Also, it seems that there were several nickeled 27's made around this time. You are much more likely to find a good 3 1/2 or 5 inch barrel 27 than a 4. Good luck. Oh, up until around 1975, the standard configuration for the 27 was a standard hammer and standard grooved trigger, standard black sights, shipping in the standard cardboard box. After that, the gun sported a target hammer and trigger, target stocks, and shipped in a wood presentation case like the model 29.