Can a scope have internal crossover error?

Discussion in 'General Airgun Chat' started by KeithW, Dec 17, 2018.

  1. KeithW

    KeithW Barn door? Where?

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    I've been tearing my hair out trying to get the scope on my springer properly zeroed. I tried different mounts, making sure my eye position was correct to rule our parallax error but still I have a problem, which is as follows.

    I zero my setup at 30 yards, however I fine tune it for lateral accuracy at 40 yards because one of the markings on the reticle falls at 40 yards. If I then check my aim points I find that closr than about 30 yards the pellets start to impact to the right of my aim point, and at 10 yards they'll be as much as 1/2" out, or even more. But at 45 yards they'll be slightly to the left of the aim point. Crossover, you'll say. Change the mounts. Which I have done. Several times. To no effect. I started to wonder if I'd maybe knocked the rifle and bent the barrel.

    So I finally changed the scope and now find pellets are lending pretty much where they should be.

    So my question is: can a scope have a lens / reticle or tube fault that might cause such a problem?
     
  2. Brian.Samson

    Brian.Samson Allowed in Sales Staff Member

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    Crossover is not caused by the mounts It is caused by cant.
    Invest in a plumb line and a spirit level and your problems will be solved.

    When you changed the scope... what you also did was... refit and re-level your scope.

    It was the action of refitting and relevelling your scope that solved your problem, not swapping to a different scope.
     
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  3. C.Eaton

    C.Eaton Confirmed Anschutz Nut...

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    You can't tell anything unless the scope's eye-piece is set for your eye, optically centred first and you use decent mounts, something like the BKL's are fantastic in this respect as they centre the scope perfectly.
    If you bench the scope and focus on your 40yd target, try bobbing your head slightly up and down and see if the reticle moves in relation to the view, if it does then either the eye-piece or parallax focus or both are still not right.

    Best way to set the eye-piece is to point the scope skywards to a blue sky (like today) and spend time making sure the reticle is perfectly sharp. Once you're happy, look out of the side of the scope at a distant object then quickly look back through the scope and see if it changes as your eye will compensate for a bad setting.

    Once everything is correctly adjusted you will be able to move your head and the reticle will remain static relative to the scope view, this is your end goal.
     
  4. Tinks

    Tinks Another tricky target at Lincs.....!!

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    I recently spent an afternoon at Doncaster Airgun Range and found to my surprise that I was actually canting my rifle slightly which was more evident on the reduced 15mm hit zones at shorter distances (below my zero distance). Fitted a different butt pad so I could shoulder the rifle as comfortable as before only this time without the cant, seems to have helped me loads.
     
  5. KeithW

    KeithW Barn door? Where?

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    Many thanks all. However ... I have set (and always set) my scope(s) with a spirit level and plumb line. I have two spirit levels, one clamps to the scope rail, the other is from Sportsmatch and screws into their mounts - not all of their mounts though. I suppose if the mounts haven't been tapped correctly then it might be screwing in at an angle, but I don't think so, somehow. So I'm pretty much sure there is minimal cant built in, as it were. As for cant when I'm shooting, I really don't think so, otherwise I'd tend to get it with my other rifle / scope combinations or would have previously experienced it with this set up. Whenever I've changed the setup I have refitted and re-levelled (to the best of my recollection).

    I always set the ocular lens to give me the sharpest reticle, and do so against a neutral background.

    I am extremely conscious about centering my eye and ensuring I have the same head position at all ranges.

    I should perhaps have said I've shot HFT for about 8 years now, and have won or been placed in competitions in all classes except Ladies (but I'm working on it). As I said at the start, I've fitted and refitted this scope with different mounts but the problem persisted. For further information, I have now fitted a different scope and mounts to this rifle (TX200) and the problem has gone away. I fitted the scope on different mounts on another rifle (using spirit level and plumb line) and still got the same result (crossover).

    Hence my original question. Is it absolutely impossible for the scope itself to introduce crossover? Obviously if it is, then I have to go back to remounting the scope (again!)
     
    Last edited: Dec 17, 2018
  6. Adam

    Adam Active Member

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    Crossover is a symptom not a cause in itself. So the scope can’t have internal crossover.

    But as Bri says it’s caused by cant and it’s possible that the scope may have inherent cant, i.e the reticle is slightly off vertical. Either faulty manufacturing or a fault has developed. I have had a scope where this happened gradually, and then one day it shifted noticeably. The etched glass sheet holding the reticle had become detached and was able to rotate in the scope body.

    I’ve seen another scope of this brand where this happened and heard of others.
     
  7. C.Eaton

    C.Eaton Confirmed Anschutz Nut...

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    Keith, what scope is it?
    If you can get hold of a scope collimator it might be worth checking the focus range and turrets against it’s scale as it will give a very good indication if there’s something weird going on internally in the scope?
     
  8. Brian.Samson

    Brian.Samson Allowed in Sales Staff Member

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    I've had spirit levels that clamp to the dovetail that aren't level ( in fact, I've never found them to ever be level, unless filed and packed ) and I've also had those sportsmatch mounts with a spirit level that screws in that's not level. I'd check both of those things.

    But look at it another way...

    Observable crossover is definitely caused by cant - no question about it, but... the reverse is also true. The cure to crossover is to cant the rifle/scope... so... the next time you experiment with that scope, try deliberately canting it to dial out the crossover. Then once you've done that (and you will be able t0) have a look to see if anything is obviously wrong.

    I have a scope where the turrets and crosshairs aren't aligned. It's a pain to zero, but there's no inherent crossover in the scope.
     
  9. Scott Hull

    Scott Hull Member

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    Scope-cant is when the scope is canted in the rings. As when the vertical reticle does not intersect the bore. That is a scope mounting issue. Fix it by rotating the scope in the rings.

    Gun-cant is when the reticle is not held vertical to earth. That is a shooting issue. Fix it by using a bubble level mounted on the scope tube that indicates when the rifle is being held correctly (reticle/tracking is vertical). Receiver/rail mounted bubbles often cannot be set correctly, so I almost never use them.

    The OP may have both scope cant and gun cant.

    As stated by others, the reticle may not always lie exactly in-line with the turrets/tracking. As long as it's not too far out, the scope is usable. If you click, it's best to align the tracking of the turrets with the bore. If you use holdover, it's best to align the vertical reticle with the bore. If the rotation between reticle and turrets are way different (obviously rotated reticle), I would not use that scope.
     
  10. Brian.Samson

    Brian.Samson Allowed in Sales Staff Member

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    Getting things level on a TX200 is a particular pain in the bum - don't assume the dovetail rail is true either. If you look back through one of the threads that Rob/Phil have written, there was a thread where they measured a TX dovetail rail and found it not only to be canted, but also very slightly angled too.

    It took me an age to get my scope set up correctly on my TX - and I did it by trial and error largely in the end. Adam has a really neat tool for getting correct bore/scope alignment. You can't buy them anymore and they're patented so technically I can't really copy the idea and 3D print one, but I'm very tempted to :D
     
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  11. Tinks

    Tinks Another tricky target at Lincs.....!!

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    A couple of years ago my favourite scope at that time broke it's wire mil dot reticle, so it was a bin job. I then found a company in USA where I could purchase a replacement glass etched reticle, so stripped the scope to see if I could change it and found that the reticle ring was located just behind the ocular lens on the end of the erector tube and was fixed in place with a threaded locking. It is highly probable that this has moved over time and rotated the reticle with it slightly, causing your problem. My broken wire reticle occurred on an HW97K and have heard of springers causing all sorts of scope issues over time predominently due to the reverse recoil or surge, which is quite brutal to delicate optical instruments. Sorry this can't fix your problem but it may help explain what you are experiencing.
     
  12. Scott Hull

    Scott Hull Member

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    An easy way to correctly rotate a scope is to put a laser boresighter in the barrel. The laser should lie on the vertical crosshairs at all distances. If not, rotate the scope in the rings.

    Or I’ll rest the gun pointed into a mirror 5yds away. The reflection should show the vertical reticle bisect the bore and the objective simultaneously.

    Even after the initial setup, it still might take a slight rotation of the scope to shoot perfectly on the vertical line at at 10yds and 25yds. Shooting paper is the final test.
     
  13. RobF

    RobF Administrator Staff Member

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    Just because you have a scope set with levels doesn't mean the crosshairs are exactly over the bore when the rifle is level. I know my TX isn't despite being set with levels. I think from memory the scope centre is 1-2mm off as measured on a clocked and levelled action on the lathe. But then that does depend where it's measured from as there's 1mm of run out down the dovetails compared to the action edge.
     
  14. C.Eaton

    C.Eaton Confirmed Anschutz Nut...

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    That's where a collimator is so useful as it works from the centre of the bore so it's easy to see if the scope is off-set despite being 'level' in the rings. It's always worth comparing the mounts for height/concentricity as I've seen some shocking misalignments over the years.
     
  15. mrgeoff

    mrgeoff Active Member

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    Setting the scope upto the mirror at 5yds sounds like a good way of setting up.

    I guess the scope needs to be optically centred in the horizontal axis for this to work?

    Thanks.
     
  16. Scott Hull

    Scott Hull Member

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    A reflective collimator looks like a good tool to get the correct rotation when mounting a scope. I won't need 10-25yd to setup the scope orientation, like I do with a laser boresighter, and it would be more precise than the mirror method. And it can be used to verify tracking vs reticle orientation. Good for mounting the scope AND testing the scope. Now I want one.
     
  17. C.Eaton

    C.Eaton Confirmed Anschutz Nut...

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    It’s a useful tool to have handy for when you have a problematic scope, plus it makes setup and initial zeroing a breeze.
     
  18. KeithW

    KeithW Barn door? Where?

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    Chris, it's a Vortex Crossfire II (now I know why they call it a crossfire!).
    I got one when they first came to market in the UK, and reviewed it for Air Gunner. I liked the glass - superb for the price - but didn't initially take to the reticle. But the reticle grew on me. However that initial scope developed a creep problem and I got it replaced. Meanwhile for a year I bounced between scopes and rifles (and there we have the first problem, too many scopes and rifles!) before coming back to the TX and Vortex and then this issue has arisen. The situation has been complicated by me developing, I hesitate to say perfecting, my technique with the TX and the Warren Edwards stock. Which, together with crappy eyesight, has meant I've lost confidence and certainty as to where the problem has lain. I have now whittled it down to either the scope or the mount - but it is just so time-consuming keeping on swapping and testing and swapping again. I've currently got a setup that seems to work (we'll find out at the Cambridge HFT Ultimate event on Sunday) which uses a different mount (un-named) and a Hawke 4-12 x 50 scope. And yes, I know, that's far from ideal for shooting an HFT comp with targets potentially out to 55yds, but I have no crossover with it and am very thankful for small mercies!
     
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  19. DaveRob

    DaveRob Member

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    I might be showing my ignorance here.... but I have a astrological telescope with a laser collimator.. I use it to Collimate the primary and secondary mirrors, but Im not sure how you would use it to align the scope with the bore and set up an initial zero. I don't wish to hijack this thread but feel free to PM me some instructions and a bit of theory please... it would be much appreciated. DaveR
     
  20. Scott Hull

    Scott Hull Member

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    Sometimes a laser bore sighter is referred to as a lase collimator. But the reflective collimator is different. I have not used one but this is what I would do:

    1st make sure the arbor (or other attachment) centers well on the bore. Then mechanically or optically center the scope turrets. Rotate the collimator in the bore and the scope in the rings until the reticle lines are centered on the grid as well as possible and run parallel to the collimator grid. Tighten down the scope in the rings.

    Fine tune with the turret adjustments. The grid lines should be at a predetermined MOA spacing, so you could use them to also adjust the elevation turret to your theoretical zero, but that is very dependent on scope height, velocity and BC, so I'd likely just shoot it at the range to set the elevation.
     
    Last edited: Dec 20, 2018
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