XD40SC Rear Sights

At first I thought it was me, but now I'm wondering if this slight misalignment is the cause of me shooting left of center.  With this pistol I am consistently shooting left of center (3 to 5 inches left of center at 15 yards - 2 to 3 inches left of center at 7 yards).  I'm usually dead on with my revolver.  

The front sight is perfectly dead center.  Neither appear to be loose, as far as trying to move them with my fingers.

Top picture is the left side, bottom in the right side.
Note that the sight appears to be off-center to the left.

Same thing here, left and right sides.

Left side of rear sight.

Top views of the rear sight.  The picture on the left was taken at almost dead center above the sight.  The picture on the right was taken slightly right of center from the top, but not by much at all.