Sighting in a Used Scope

A scope will be brought back to zero for resighting by the following: Align your scope before you zero. Using a collimator, which is an optical device that attaches to your muzzle and adjust your reticle until it is centered on the collimator.
You can also bore sight from a resting position and once you are on paper at 25 yards you will still have to do a sighting in from 50-100 yards using your scope dials to manipulate your crosshairs and bring them to zero for this particular gun.