my guess is the mounting holes are not lined up with the barrel. Take the scope off and run a string from the center of the muzzle to the back screw of the mount or just run the string in line with the screws and see how far off muzzle center it ends up. I would bet you will find the screw holes are just a little out of line. You will need to find some sig-z rings or change to a Redfield/Leopold mount with the windage adjustable rear ring.