A couple more thoughts:

As you probably know, the Model 27 was the direct descendant of the .357 Registered Magnum, introduced in 1935. At that time, barrel lengths were all ordered with the gun and could range from short to 8 3/4", in quarter inch increments. In the postwar period, when the .357 Magnum was reintroduced, there were lots of them issued with 6" barrels. I once owned one from 1952 with the 6" barrel. For some reason, in later production (from 1958 onward, when model numbers first were used) the 6" was eliminated and the 6 1/2" became the standard for a mid-length barrel (between 5" and 8 3/8"), until 1967, as noted above. Sort of a weird sequence, it seems to me. I'm sure there was a reason.

Also, the N prefix replaced the S prefix in the serial numbers during the -2 years.

__________________
Jack
SWCA #2475, SWHF #318