If you are new Smith & Wesson enthusiast, realize that there is a substantial learning curve to knowing the ins and outs of model numbers, and model numbering variations. Working from my limited experience, I can remember when there were only 25-2s in .45ACP and only in a 6 1/2 inch barrel. If there were many .45 Colt made guns, they were few and I never saw or read of any. When the .45 Colt guns were introduced, they were called 25-5s and initially made in only 4 inch barrel. You could rely on the fact that a 25-5 was a .45 Colt and a 25-2 was a .45 ACP!
Barrel length had noting to do with the model designations, and I don't believe they ever have.
Now we have several configurations of 625 in both calibers and the 627 has a lot of variations and even one in .38 Super caliber. The dash numbers represent engineering changes in lockwork and frame changes more than anything else.
The bottom line is, that you just have to memorize the model numbers, caliber etc.
Now given that, there is some consistency in the model numbering and frame material. Plain two digit numbers starting with 1 or 2 are usually carbon steel, stainless model numbers begin with a 6, and alloy frame guns with a 3. Beginning in 1980, with the introduction of the L frame, the 586 was carbon steel and the 686 was stainless.
All this can be confusing to new owners and I may even confused myself here!! And I am sure there are some exceptions to the generalities I have tried to cover.
So don't be shy, go ahead and ask questions to learn the Smith way. And get the "Standard Catalog of Smith & Wesson" to learn even more.