Track down the reason for a POI shift

Discussion in 'Steyr' started by DaveRob, Jul 26, 2018.

  1. DaveRob

    DaveRob Member

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    I have a POI shift, ( up and right ) that I think is temperature related, I think it is NOT the scope as its gone as far as 14 clicks on my Nikko in a shoot at over 25 degrees and that seems like too much to be scope.... I cant confirm if it goes back to my original zero as we haven't had the 10 degrees I set it up in since then... It was over 8 clicks different at around 20 degrees.

    Notice the 'I THINKS' up their ..... Im happy to be corrected in my thinking..... so its in my head that this is due to a non free floated barrel, Ive unscrewed the end grub screw that bears on the last ring in the chassis.... no change fault still apparent.

    To start the investigation Im going to do a 30 shot string over my combro, should I do this with a cleaned barrel or with the barrel 'as is'... about 150 shots since its last pull through. I could just pull the whole thing apart, clean everything... free float the barrel... strip the reg and check the pressure and creep and put it all together.... But then I wouldn't find out what the fault was, and I would rather know the reason.

    Ill post the results of the shot string here after Ive done it but it might be week after next as Im going away soon for a few days..... For the shot string FPS should I take a shot every 60 seconds or just bang them through?

    As always thanks in advance.

    DaveR
     
  2. NeilM

    NeilM Well-Known Member

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    What rifle are you using?

    I'd be inclined to re zero the rifle with the temperature at around 18 to 20 degrees, I know you are up North but having a zero set at 10 degrees could easily give you scope issues in our present temperatures.

    As far as chrono strings, try shooting them at 30 second intervals and maybe try a few in quick successions, I would hope you get very little difference, but replicating actual competition timing is probably more useful.
     
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  3. DaveRob

    DaveRob Member

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    Steyr challenge hft with a MK 3 Nikko 10x50x60. Thanks for a swift response

    DaveR
     
  4. NeilM

    NeilM Well-Known Member

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    I've not owned a Steyr in a long time, but I don't think they have a reputation for being temperature sensitive. If you have the barrel floating within the confines of the chassis, that's about all you can do in that respect.

    Wait for a few more responses, but I'd be looking at the scope.
     
  5. RobF

    RobF Administrator Staff Member

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    Firstly chrono. But make sure the gun is at the temp you suspect where the issue occurs. Often guns can take 30 mins plus to get the hot or cold soaked into where it affects things, and in sun and out of sun temps can be 20 degrees away from each other... (seen snow on ground and 15 deg in sun, and seen 15 in hot sun in the shade, 35 in it).

    Hopefully whatever issue you're seeing is repeatable, and by varying elements you can get a pointer.

    Fill pressure is not to be ruled out.
     
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  6. Conor

    Conor Never been banned from sales Staff Member

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    Is the barrel touching any of the holes it goes through in the chassis?
    I bet that’s the cause, just taking out the grub screw doesn’t solve anything, there is a white nylon/delrin plug under that grub screw; it’s in contact with the barrel, it needs removing.
    Also the chassis is a different material to the barrel, aluminium and steel, both with expand and contract differently so if one touches the other then there will be POI issues when shooting the gun in different temps.
    Also have you checked the velocity?
    Are you using a raiser rail?
     
  7. DaveRob

    DaveRob Member

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    Yes the barrel touches the chassis. Both at the last chassis hole and the middle one

    I intend to chrono the shot string

    I am using a rider rail as my Nikko wouldn't fit without it

    Cheers Conor
    DaveR
     
  8. DaveRob

    DaveRob Member

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    Might be a few days befor I can do the chrono tests but I'll keep this in mind and do it after the gun has been in the sun a while. I'll post the shot string here when I can

    Many thanks

    DaveR
     
  9. Darron

    Darron Reformed Bandit

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    What he said.
     
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  10. Conor

    Conor Never been banned from sales Staff Member

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    Forget the chrono and visit a local engineer and get the barrel free floating. Machine the holes out to give a sufficient gap around the barrel 18mm hole should be fine
     
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  11. hmangphilly

    hmangphilly Not quite a full phil

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    What he said again
     
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  12. C.Eaton

    C.Eaton Confirmed Anschutz Nut...

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    +1 on getting the barrel not touching.
    Manufacturers should do this as a matter of course during design/fabrication but I guess indoors at 20 degrees is easier than outdoors at anything from -6 to 35 degrees....
     
  13. DaveRob

    DaveRob Member

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    Thanks for this Conor.... tbh its the thought I had from the start with this issue, if nothing else it makes it 'feel right' to me.

    Their seems to be 3 options

    1...I can machine the chassis to 18mm holes

    2...I can machine the barrel locally around the chassis points that are touching

    3...I can get a CZ or Walther barrel of smaller dia and sleeve the breech and crown back to 16mm to fit the breech and stripper

    In order of easiness it goes 2 then 3 then 1
    options 2 and 3 give me the ability to return the gun to original spec should I need to

    Is their any reason why I shouldn't do 2?

    Thanks for all your inputs.

    DaveR
     
  14. Ratinator

    Ratinator Well-Known Member

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    Have you tried rotating the barrel or shimming at the breach ?
    I had a Steyr barrel that when I added a 2mm wide strip of tape in the opposing area lined up perfectly.
    Also if it has 2 barrel grub screws tighten in a different sequence .
    Ultimately your best fix is the 18mm hole , if you go down the barrel route I would have thought a 15mm sleeved upto 16mm the best for free floating .
     
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  15. Omega

    Omega New Member

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  16. TenMetrePeter

    TenMetrePeter Paper punching member

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    I would think the barrel has all kinds of residual stresses from fabrication and machining even part of it in the middle could bend it.
    Necking off the breech end isnt a problem
     
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  17. Omega

    Omega New Member

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    Hi everyone just getting used to this mail lark, I had a similar Poi the other day in 30 degree heat,mine shifted 25 clicks from original winter set up. I shoot an Anschutz 2002 with a Falcon T50 10-50x60 . I am new to HFT and reading through past comments and info I now double check before shoots.
     
  18. DaveRob

    DaveRob Member

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    The best fix is the fix I should really be doing then

    DaveR
     
  19. subaru swift

    subaru swift Active Member

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    If it was me, I would just fully free float the barrel by making the chassis holes a tad bigger like 18mm what's been said all ready.
    I did my older HFT & FT steyrs myself, but they are not the newer chassis.

    These crazy temps do not help both the rifle & the scopes! I was a couple of clicks out within 2 days due to the temps.....one day was around 20c the other day was around the 32c mark :(
    Just wish this hot weather would do one now.
     
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  20. Adam

    Adam Active Member

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    I fail to understand why manufacturers still insist on designing and marketing airguns for outdoor target shooting that do not have free floating barrels. It's a no-brainer. If barrel is fixed at both ends, any flex of what it's fixed to, or expansion or contraction of that with temperature or fill pressure, is going to shift the zero.

    I understand why it's not of huge importance with indoor 10M guns. but there's no excuse for the AA FTP or the specific FT/HFT versions from Steyr, Anschutz, FWB et al.
     
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