No, it's definitely a k frame. Look how close the top of the cylinder release is to edge of frame. There's no gap, you'd see a gap on an n frameNice, my early morning observation skills tell me I see a 624, but I may be off. (66?)
Except for the Model 66's forcing cone I might agree that is one of the best S&W revolvers.
I have to agree with Sodacan, a 2.5" model 66 is good as gold! It is difficult to find a better or more practical revolver.
I have never owned a 2.5" gun until March of this year. Bought a 66-2. It certainly is not perfect, but good enough for me. Oh, did I mention that it shoots quite well? Also have a 2" 10-5 R.B. I put Herrets on both of them. Bob