You can try this. This is a trick that gunsmiths use on scopes that run out of adjustment for windage when the firearm is using non-adjustable windage mounts. You wouldn't believe the tiny bit of a shift in a scope base can make in correcting windage issues. So when I explain this to you, imagine the rear sight unit and the front screw is the front base for a scope and the rear screw is the rear base for a scope.
Start by loosing the rear sight unit's rear screw. With a hammer (brass, plastic,) tap the rear of the rear sight unit to the left. Don't be afraid to give it some pretty good taps but obviously don't beat the #### out of it. Once you tap the rear of the rear sight unit, tighten the screw. You can choose to go to the range and test it now. It will probably be enough to correct it but if its not enough, then you can do the same thing to the front screw of the rear sight unit only you will tap it to the right instead of the left. If you bring a gun vise to the range with you and the proper tools, you can do all this while at the range.
You can also do the same thing to the front sight unit with again imagining the rear screw as the rear scope base and the front screw as the rear scope base. I would only go that far if the rifle was successfully sighted in with the rear sight being done but the front sight post sits too far over one side in the sight unit for my liking.
