Mark III 22/45 Mag

[One Eyed Jack]

Why do the new Mark III 22/45 mags have a cut out on the uper left side (Thumb button side)

Old Mark II 22/45 mags work in the new Mark III 22/45

 

[Bullseye57]

This upper window is found on all Mark III magazines and it is Ruger's attempt to have the Mark III trigger spur engage and seat a partially locked magazine without having the pistol disabled by a loose magazine. The trigger spur is supposed to hook underneath the upper bump and push it upwards. As you have noticed the spur is scalloped and doesn't enter into the area where the metal body is located which is why a 22/45 Mark II magazine works fine in the newer model guns.

R,
Bullseye

 

[One Eyed Jack]

Thanks for the answer