Second series Sport(as already stated) It 'sports' the Coltmaster rear sight that all seconds 'sport', unless fixed. Here's a 4" MT with same sight...
[Linked Image from hosting.photobucket.com]

3rd series used fixed, Accro, or Eliason sights across the models.....
[Linked Image from hosting.photobucket.com]
[Linked Image from hosting.photobucket.com]
[Linked Image from hosting.photobucket.com]

first series used fixed (with 2 kinds of fronts), 2 different dovetailed adjustable rears with 2 different apertures depending on front style. Round notch for use with bead sights, square notch for use with patridge

edit to add...
Colt also used a different, cheesy, fragile adjustable rear on its 3rd series Targetsman

Last edited by huntsman22; 11/28/22.