Open the action and look through the bore at the 25 yard target. Center the target in the bore. Now center your crosshairs on the 25 yard target. Keep the gun still and keep looking in barrel in scope, back and forth, making sure target is still centered in both.
This is pretty rough for adjusting things, but it has seemed to work pretty well for me to avoid shooting off the target and having to guess where the shots are hitting when things are way off from the start.
Just a thought - doesn't require buying anything.
Ranger413