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Old 31st May 2014, 10:15 AM
Arthur Arthur is offline
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Join Date: May 2014
Location: North West
Posts: 11

ugh - found the answer by re reading again the link maestro sent.

But even with this info - if the windage is out by 25mm at 13m is that beyond acceptable? Just asking before I put these mounts in my milling machine (and then go out and buy some new expensive mounts after I've ruined these ones).

3.5.2 Lateral Misalignments of the Scope
These can be seen from top view of the rifle. The average shooter attaches much more importance to these problems than they really are. In summary I should say that they are not really significant in practice and are hardly perceptible if the scope is properly zeroed. Let's see, why:

1. Scope is offset - this is the case when the scope is not in the symmetry plane of the rifle but it is shifted to either side. For example, this happens if the prism width of scope rail and mount ring is not the same but you put it on with some lateral shimming, though. If you have a 10 mm rail and a 12 mm ring base then the offset is (12-10)/2 = 1 mm. This displacement can be handled in two ways (in the following examples we assume that the scope axis is 1 mm right from the barrel axis):

Keep the parallelism, i.e. zero the windage in a way that the crosshair is 1 mm right from the POI on the zero range as well. With this setting, the rifle will shoot 1 mm to the left on all ranges. It's not a big deal, considered that you have to hold off even multiple killzone diameters for the wind.
Zero the windage on 30-35 yards (halfway of the possible ranges). This means that the windage is absolutely correct on this distance, shoots to the right with 0.7 mm at 55 yds and to the left with 0.75 mm at 8 yds.
It is obvious that these inaccuracies should not be seriously dealt with.
2. Scope is not parallel - the reason can be a scope prism milled with an angle or deformations in the mounts, scope or rifle. It is important to mention that the pellet's trajectory is determined by the relation of the muzzle and scope so even a perfectly mounted scope can be angled (related to the muzzle) if the barrel is bent. But this angle can be corrected with the scope's windage turret and is not extrapolated with the distance. So if the scope rail has a 1 mm turn on its 12 cm length, this does not mean at all that we would shoot 42 cm to the side at 55 yards, it will be 1-2 mm only (determined by the offset of the front lens related to the bore axis) and this does not result in too much trouble, see the previous paragraph above.

We can conclude that the lateral misalignments of scope (which can be seen from top view) do not really endanger the accuracy. The real problem occurs only when the scope is rotated around its longitudinal axis, i.e. the cross-hair is not levelled. Although it seems less daunting, but it is the real danger, because in this case the elevation adjustment affects windage as well, and we have a much greater chance of canting errors - and these are not a few mms any more but severe centimetres at greater distances.
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