[Codex]

OK I may have found an explanation in the most unlikely place, a patent for the target reticle on telescopic sights believe it or not, but I am still not a 100% convinced this why the sights are offset.

Source: http://www.wipo.int/pctdb/en/wo.jsp?...7&DISPLAY=DESC

GYROSCOPIC EFFECT: A spinning projectile from a rifled barrel is, in effect, a free gyroscope. When subjected to a twist or torque, it tends to rotate about an axis perpendicular to the axis about which the torque is exerted. The front wheel of a bicycle is a good illustration of this phenomenon. If the bicycle is tipped to the right when rolling forward, the front wheel resists tipping and instead its axle rotates to the right, turning the bicycle to the right.
While following its path, which is constantly curving downward, a projectile is subject to a force (air drag) on its nose from underneath, causing a twist or torque. If its spin is clockwise, this upward torque causes the projectile's nose to rotate and offset slightly to the right (like the bicycle wheel) as seen from the rear. This offset causes air drag to act unevenly and to push the projectile slightly to the right.
The effect of gyroscopic drift is difficult to analyze precisely because many variables are involved. Drift tables, which have been determined mainly from well-controlled army and navy tests, indicate that gyroscopic drift is roughly double that of Coriolis drift, and thus is also negligible for most purposes. It is interesting to note that with counterclockwise or left-twist barrel rifling, gyroscopic drift is to the left in the northern- hemisphere and more than cancels the effects of coriolis drift.