The Model 27 is called simply the .357 Magnum, because it was the first one ever made. They started making these revolvers in the late 1930's, stopped in the late 1990's.
It is based on Smith's N frame size, a large frame.
If you measure te barrel from the muzzle to the extreme end right in front of the cylinder I believe you will find it is an 8 3/8". The Mod 27 is the model number, the -4 is the change number, which indicates an engineering change and can give you an indication of the period your revolver was built. I estimate it is from the late 1960's.
With the longer barrel the gun should be a tack driver.
I have owned 6" and 4" versions of the .357 Mag, and I loved them. The N-frame has a lot of fans - it's big, but smooth as glass and really accurate.
The Mod27's are very collectable and priced pretty high, depending on condition. 75% soulds pretty worn looking, but I would never consider refinishing a gun like this - it would lose it's collector interest and value.
I can't even estimate the value, but if you Google the S&W forum there are a lot of specialized .357 Magnum experts there who could.
It is a great revolver, and I'd certainly keep it - not many around for sale any more.
Thanks Mark! I stated 75% but the blued finish is great , a few light scuff marks and some bluing worn around the cylinder! It is definitely a tack driver, i have killed wild hogs at 60 yards with the open sights!
The model 27-4 was discontinued in 1994, barrle length close to what you expressed is 6 1/2" or 7 /3/8" depending on how you measure. Value varies if it's four screws or three screw mounted to the frame (grip screws don't count). Four screws sell from $850 to $325 depending on condition, three screws sell from $700 to $200 depending on condition. The top in is new in box and the low end is in usable condition.