Its quite normal on a quality telescopic sight for the designer to limit turret adjustment to 5 revolutions as he wishes to use the best part of the lenses – which is the centre or as close to centre as possible, this is especially necessary on higher magnification scopes. Consequently, its possible for some guns, especially airguns that have parallel scope mounts for the scope to run out of adjustment.
The answer is to use a shim to ‘tilt’ the scope forward. The shim goes between the scope and the underside of the rear mount. The shim is ideally fabricated from soft metal such as a lead tape used in golf club weights, or even folded tinfoil to a thickness of approximately .25mm. Another option is to use adjustable mounts. For example Sportsmatch offer one piece mounts that adjust up to .75 mm of tilt and two piece mounts that allow .4mm of tilt, though it is also important to have the two mounts the correct distance apart to avoid a misalignment.