According to the S&W 3rd edition ( standard catalog) reference guide...
Model 36 ( no dash ) started in 1957 ....but within that no-dash period from 1957 thru 1966 there were some changes in the guns. In 1962 there was an internal hammer alteration at serial number 295000 / in 1966 there was a Thumbpiece change ( no details other than that in the book - that I see ).
Model 36-1 starts in 1967 ...and it does show it was to indicate a 3" Heavy Barrel.
and the book goes on for most of a page....thru engineering 36-10 ...in 2006.
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I'd recommend you pick up a copy of the S&W book ...if you're really interested in finding out more about S&W revolvers...there is a lot involved in many of the models ...that might affect what you choose to buy and shoot.
Most of us that collect and shoot S&W revolvers...tend to stay with 5 or 6 models, where we concentrate our knowledge ( for me its in model 18's, 19's, 27's, 28's, 29's (blued and Nickel) ...and 617's, 686's, 66's, and 629's(in stainless) ....and I have about 20 S&W revolvers now....different barrel lengths, etc...and most of them, I shoot quite a bit.
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The differences between a no dash model 36 ...and a dash 1 in the model 36 ....can be very different between a model 27-1 and a 27 no dash....
but that's why the reference book is over 400 pages, lots of data, lots of photos ...and its not just revolvers...its their line of semi-autos too..and performance center guns...etc...