Both guns in the photo are J-frame Chiefs Specials.
The one on the left has a 5-screw frame. Its stocks will fit an I-frame
up through 1953/54.
The one on the right has a 4-screw frame with a longer grip frame
and also longer oval trigger guard. Its stocks will fit an I-frame made
between 1953/54 and 1961, when S&W eliminated the I-frame.