Well my X-Cal developed the same problem today. Noticed I was shooting a little right of center for some reason. I had previously zeroed the rear sight and it had been right on. Went to adjust the rear site and what do ya know it moved just by pressing the screw driver against it. Then I had no problem moving it back and forth, almost the distance of the slot, easily with my fingers. I'll be calling Eagle on Monday to see of they can help me out.