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Old 14th October 2015, 10:04 AM
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RobF RobF is offline
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Join Date: Mar 2010
Member of: Southampton Buccaneers, Parkstone, South Dorset
Location: Poole, Dorset
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Originally Posted by skires View Post
Er ... I think you are having a slight moment?

As I understand it if the scope isn't in perfect line with the breech/barrel then you will be bang on zero at your chosen zero range. You have zeroed that range for elevation and windage. However, at distances a good way away from your zero you will firstly ( close range ) impact on one side of the vertical, and then at the other extreme range from your zero ( furthest range ) you will impact on the other side of the vertical.

Hence the term "Crossover". You poi's will actually cross over your vertical and will only be bang on horizontal zero at the range that you zeroed the windage on the scope.

I've read a bit on this re airguns and a formula I once saw ( I think ) was actually showing that the scope can be quite a bit out of line with the barrel and the crossover error was still very very minimal at airgun ranges. There was a far far greater chance of any off horizontal error at various ranges being due to light cant of the rifle or the cross hair being slightly off perfect vertical ( or, of course, PA error due to eye misalignment with a set distance focus ).

So I'm not sure it's a problem to begin with.

So, theoretically, although the scope is only 1mm off centre to the bore ( horizontally ) it will hold zero at your zero range ( say 35 yards ... because you've set it at that ) but at 55 yards it may be several mm's off. Similarly ... but on the other side ... it may be several mm's off at very close range. So if you try and adjust the windage turret to compensate for the very close ones ... you will now be off at your 35 yard zero ... and even further off at your max distance.

Is that what you meant? Sorry if that's a Granny and her eggs post.
I had a chat with the man from Kahles in Lithuania, because I'm fairly convinced (until i get off my backside and go down the tunnel and actually prove it) that there's some crossover issue on my TX. Zero'd indoors at 25 it's going against a very feint breeze to about 5mm at 10yds, and taking around 10-15mm more than i'd say feels right at 55 with the wind). Close left, long right.
Anyway, suffiice to say it was only a quick conversation and I asked if this is possible. A couple of us had had a chat about if when you dial a scope, does it alter the LOS parrallel to the bore, or does it angle it... eitherway unless you've got it aligned you will see an error. If it offsets parrallel, then it can't ever match the angle the scope and bore deviate by... if the LOS changes angle then it can match the angle, but if there's any offset as well, that can't be dialled out.
The chap from kahles agreed it was quite possible what I was seeing was due to misalignment, but although his english is superb, it was a quick chat and I didn't quite get to the bottom of what the solution was.
There was an interesting post on the BBS about cant as well, which I also need to check... because the TX lacks any really good alignment surface to plumb against... so that could also be it. Or it could be in my head.. or me. I never felt confident with her over there and found myself aiming for something I couldn't see... but then that could actually have been the conditions.
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