Kiwi,
Kuduae, makes a good point.If your trip to the range with heavy bullets, doesn't square you away, check the elevation turret of the scope.Some scopes provided a means to lock the setting( to prevent accidental movement). If there is(are) a (some)small screw(s) on the top or side of the dial, loosen them (don't back them all the way out)and try again.If that works, be sure to retighten everything.
Mike