the security,service,speed-six family are akin to the smith K-frame series in size. the main difference is the lack of a sideplate...the internal remove from the bottom of the frame.
the gp-100 took ruger DA handguns to the next level by adding the non-rotating/offset ejector rod, the quick change front sight and the stud mounting of the one piece rubber grips w/wood inserts. the gp series is akin to the smith L-framein size.
the gp-100 will last forever when fed a regular diet of .357mag loads. the speed-six packs much easier and should outlast, when fed .357mag loads, most owners