Just for fun, the text from an old post by me on the subject:
..............................................
A few years back (about ~2000) I researched the M27 barrel lengths re: number of years each barrel length was "offered/cataloged" in S&W documents (Annual catalogs, All Model Circulars, Price lists). For Postwar manufacturing, the .357 Magnum (pre-M27) and Model 27 was offered in the following barrel lengths for the following number of years:
6 inch barrel.......- 1946 - 1974 - 49 years
8.375 inch barrel.- 1946 - 1991 - 46 years
3.5 inch barrel....- 1946 - 1979 - 34 years
5 inch barrel.......- 1946 - 1979 - 34 years
6.5 inch barrel....- 1946 - 1968 - 23 years
4 inch barrel.......- 1980 - 1991 - 12 years
Notes:
1-Prior to Cataloging the 4", Special orders accounted for all 4" Production
2-Model 27 sales (in general) very sluggish after the Model 19 introduced
3-Model 27 4" cataloged the first time in 1980, same year that the L frame was introduced
4-Duty usage of 4" M27 probably slow as compared to the (lower cost) M28 Highway Patrolman after 1954
5-Almost all Nickel 4" models noted to date have been around 1980 production M27-2, all with TT/TH/TS/WO/RR !!!!
6-Years cataloged may not directly correlate to actual production numbers, but it certainly speaks to general availability and order ability, after-all folks usually buy what is offered and knowing that the factory didn't usually build to order in later years, the ability of a consumer to call and order a non-cataloged barrel length had almost stopped by the mid 1970's.
7- The above is for "standard" production guns; it does not cover any Commemorative or re-issue special editions. (Both the 3.5 and 5" were re-introduced at least once) Update – the current Classic line info isn't included in the above.
8- For those of us that remember the 1970's and the fact that Model 27's languished on store shelves for many many months back then, it's curious to think just what S&W was thinking when they introduced the 4" barrel length when they did - exactly the same time as the introduction of the L frame models. With poor sales of N frame 357 Magnum leading up to 1980, one has to wonder just how many 4" M27's actually sold during the years that they were cataloged. Can't be that many in the overall scheme of things. Whether you are interested in the pinned and recessed versions (-2), the transition models of the -3 or the regular -3 versions, there are not all that many to be found.
The above information is meant to note what the factory was offering, not production quantities. Based on the number of year's offered and general observations, the 4 inch model is the hardest to find.
It is amazing to me that the 3.5: and 5" are viewed as being the scarcest. In the NW, it seems like I see more 8.375" models than any others.