The "S" for Specialty grade is obvious now that I think about it. It does indeed fall into the Lightweight category according to the number of screws. It has 2 3/4" chambers which I believe are original but am not sure when the change was made from 2 1/2" to 2 3/4"---can anybody help here? It is choked full and full which makes it a long range gun---the gun is in beautiful condition so am not sure I would want to open up the chokes but if the chamber length has been altered, well maybe have to think about it.