Airgun Accuracy

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Chairgun and the Big Nikko problem

“The crosshairs are moving when adjusting the side focus or parallax knob”

See the video I made with my mobile phone. The quality is not very good. It’s a hell of a job to keep the camera steady and in the exit pupil. But you will see what happened when I adjust the parallax knob on my Big Nikko.

Link to the video: Video of the crosshairs moving on the Big Nikko

Last weekend I was preparing for an 100 meter smallbore and airgun match. It has been quite a while since I last shot at 100 meters. So I thought I would check the zero of my .22 LR Anschutz and the .22 Theoben Rapid. Both have a Nikko Stirling Diamond Sportsman 10-50×60 MKII scope on top (the nikko with the low green turrets). To check the zero at home I used an bore sighter / collimator from Leupold: the Leupold Zero Point.

LEUPOLD ZERO POINT BORESIGHTER

LEUPOLD ZERO POINT BORESIGHTER

It attaches to the muzzle with a magnet and when you look through the scope you see an image like this:

Zero Point image when looking through a scope.

Zero Point image when looking through a scope (image from the www and not a big nikko) .

You can then adjust the scope until the crosshair / reticle matches the position on the grid you want. I usually use a setting I measured at a zeroed rifle scope combination and wrote down. But it also helps a lot to get a new scope on target when you just set it to the 8 or 16 inch setting at the grid for a 50 meter zero. For 100 meter zero I need to set it around 20 to 24 on the grid for both the .22LR Anschütz and the .22 airgun at 40 joule.

What I noticed with both the Big Nikko scopes is that the crosshair moves up and down when the side parallax (or side focus) knob is turned. And not by a little, but by 2 inch and 4 inch on the grid for two scopes respectively! The error was very consistent. I turned the focus knobs many times and every time the crosshairs moved up and down again the same distance. And they do this shift gradually: The crosshair keeps moving with the increasing movement of the focus knob.

The crosshairs both moved upwards when going to the larger distance setting on the side focus / parallax knob. For a focus setting from 10 meter to infinity the reticle moved four inches up on the grid for the one scope. This means a four inch movement of your point of impact at 100 yards. Or approximately two inch at 55 yards which is the long field target shooting distance. This is not a small error. As has big consequences when you want to use Chairgun or other ballistic software to make a sight table or scope tape for your Field Target rifle. It will never give a correct match between calculated and real world elevation settings. And because in field target you use a different focus / parallax setting at each distance you shoot, the crosshair will move as well.

The crosshairs in the Big Nikkos are moving up with increasing distance. This will mean that the elevation correction needs to be much larger than expected from ballistic software when going to a greater distance.

This does not mean that these Nikko scopes can not be used for proper FT shooting. When using elevation turret settings that were actually observed when shooting, these settings will still match. This is because the error is very repeatable. But when you want to use Chairgun or other software to make a sight table or turret tape for your field target rifle it will just not work. And that is how I usually use Chairgun: To make a table for every 2 meters when just zeroing the scope at 8, 20, 30, 40 and 50 meters.

An other error I noticed is that both scopes moved the crosshair when adjusting the magnification. About  a half to 1 inch@100 yards up and down. This happens when moving the magnification, or zoom ring, from one direction to the other. And instantly when starting to turn.

I also tried my Sightron SIII LRMDCM 10-50×60 scope the with Zero Point bore sighter. This Sightron did not move the crosshair when adjusting the focus / parallax setting or magnification setting.

My conclusion: With my two Nikko Stirling 10-5-x60 MKII scopes I can not use Chairgun to calculate elevation settings. I need to use real world observed elevation settings to click for the distances, and should not adjust the magnification setting. No big problem for target shooting at fixed distances. But not very handy when shooting Field Target.

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4 thoughts on “Chairgun and the Big Nikko problem

  1. At last some one that has finally found problems inherent in ‘most’ scopes.
    You will be amased at the shear amount of scopes that do such a thing and much worse from cheapies to the most expensive scopes produced.

    Easy quick check is a bore sighter often called a collimator. Producers use collimators but set focus at a preset position for checking! Even supposed freelance scope testers fail to pick up on this major issue and just do the box test or simulated firing shot test pointless.
    First time found and understood this problem was in 2002 and reported to distributor twice as two they replaced did same thing but ret went diagonally.

    I mount scope on a rail in to a substantial solid mill and lock the beds up, nothing moves rigid. Mount camera behind scope then all set to go. To my knowledge there is only one company that has understood theres major problem and rectified over 5 1/2 years ago.

    New high end scope released last year, how can this scope be used and subject to temperature shift. Shown here at around 10 degrees, was massive movement at 14 degrees.
    [video src="http://vid1140.photobucket.com/albums/n563/Jonhareng/Scopes/Ret%20Shift%20luke%20warm.mp4" /]

    Heres another about two years ago after two repairs. Mortars 9.5mm wide, bricks 210mm long x 65mm, distance 24 to 25 yards
    [video src="http://vid1140.photobucket.com/albums/n563/Jonhareng/Scopes/DSCN4522.mp4" /]

    So to cap test scope but that’s only at that temperature.

    • Hi Jon,
      Thank very much you for adding your very good video’s. I really struggled to get a good image of the shift with my cell phone camera. Your video’s are much better and show the problem in a very clear way.
      Looking at the reticle your first video (ret shift luke warm.mp4) it must be the Sightron SIII Field Target scope 10-50X60 FTIRMH. My own Sightron SIII LRMD/CM (which is the older type, not the FT version) does not show any reticle shift. So did Sightron change the scope design for the FT version? Or is this problem specific for the individual scope?
      Another thing I noticed is that my Big Nikko’s only show a vertical reticle shift. Your Sightron video shows a horizontal shift. Your other video shows a diagonal shift.
      The vertical shift in the Nikko will be compensated for when an FT shooter uses real world clicks to calibrate his scope for the different shooting distances. The horizontal shift in the Sightron is a much bigger problem because it is not normally compensated for when dialling in for the distance. This scope is practically unsuited for FT shooting because of this problem.
      Really curious to know which is the scope in your DSCN4522.mp4 video.

      Kind regards, Sven.

  2. No its not the S3 or the modded FT scope though have seen three do much worse.
    Scope in question had minor shift below 10 degrees, the warmer it got the more diagonal shift.
    I do have a video of a certain manufacturer attempting to understand stating shift is cured. Shame they used on max mag through a collimator though told not to and use lowest mag, of course there wont be any disconcernable shift showing up it hoes out of focus +/- 5 yards. However upon return low mag showed the same symptoms as previous 10 attempts to fix.

    Most of the shifts have seen in a massive range of scopes from cheap to expensive are from lowest range to 65 yards with odd one or two more progressive in to 100’s of yards. Looks like crossover to the untrained, producers blame pa error as well.

    First noticed these effects way back in 1994 with a Mark 1 Tasco, clicks didn’t seem progressive or match up with dialling used for other scopes. Only one way to do it shoot the ranges and don’t be surprised to see big uneven jumps.
    Problems arise when rets moving off diagonally and dependant upon temp as to the variable amount of shift.

    I’ll find a video on youtube a supposed scope tester to the trade and blatantly missed above symptom just going with box test and simulated firing cycle.

  3. Have a look all he has done is move the scope focus to 100 yards, see green dot jump. Suspect the 2.3MOA shift is to do with this and sloppy tolerances.

    Not much on this one but who knows if adjusted focus from 70 yards to 10 yards. 1min in look where green dot is, 1min 25 sec all he has done is adjust focus from infinity to 100 = lateral shift.

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