The Mk I holds 9 rounds and has a magazine release on the heel of butt
The Mk II holds 10 rounds, has the magazine release on the heel of the butt and is scalloped at the end of the receiver so that the bolt can be grasped easier
The MK III holds 10 rounds and has the magazine release on the side of the frame. It also has a loaded chamber indicator and will not fire when the magazine is removed
There is some more slight mechanical differences but I cannot recall them at the moment
what about the 22/45s are they as good as the standard rugers