Considering shiming the Challenge FT barrel

Discussion in 'Steyr' started by astra, Sep 17, 2019.

  1. astra

    astra Member

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    After reworking the "genious" chassis design of Challenge - opening the chassis 3(!) holes for free floating the barrel I started considering shiming the barrel. Reason is - while no more temp shifts (proven between 18 to 36 degress) still some sudden poi shifts at 9 and 3 o'clock and then back to zero. It might be the pellets but the barrel seems fits quite loose the chassis - it is simply sloppy when not tightened. And those sharp screws are real pain to tighten the proper and repeatable way. The screws contact spots have nothing in common with the LG110 barrel design and it is a game of chance to align the barrel with the chassis and scope.
    If I have to summarize: the changes in Challenge design are real ... challenge to overcome and rework to get back the LG110 properties.
    Just in case: can anybody who has made barrel shiming, give me a practical advise, before I start?
    I have 0.1mm copper sheet that looks like a good candidate for shiming material.
    Thank you.
     
  2. suds

    suds Senior member

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    I have shimmed a few barrels, I would suggest that you use plastic shim as copper is very soft and may be difficult to fit as I usually end up using 0.002” or 0.004” shim. I get my shim from RS Components it come in a pack of assorted from 0.002” to 0.020”. .050mm to .500mm
     
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  3. astra

    astra Member

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    Did you wrap barrels from all around or just partially? I tried to see how much I can wrap copper foil around the barrel and saw that with 0,1mm foil I could only shim the bottom half of the barrel up to 9 and 3 o'clock. Now it seems the barrel fits quite tight and no more lateral movement is possibile. However, it can still move vertically if the screws are not fully tightened.
    Tried to unscrew and screw them again and got two clicks vertical shift... (one click is 1/8 MOA)
     
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  4. suds

    suds Senior member

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    I cut to go completely round the barrel with no overlap. If you can make it a nice tight fit that will give you the best result. If very tight smear a little oil it the breach and it will help it to slide in. I do cut a small V in the shim to allow for the grub screws to grip the barrel only. Dave P.
     
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  5. astra

    astra Member

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    Thanks for sharing your experience, Dave!
     
  6. astra

    astra Member

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    Could you, please, share the link to this shim pack as I was unable to find it on RS site. It may be it has become obsolete?
    Thank you!
     
  7. suds

    suds Senior member

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    Just go to R S Components and search plastic shim.
     
  8. suds

    suds Senior member

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    Just looked on Amazon and they sell “Assorted plastic shim packs”. They are much cheaper here . All the best Dave P
     
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  9. hmangphilly

    hmangphilly Can't Re Member

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    Is the barrel mounting system different between the challenge and the old 110 ?

    I don’t understand this issue
     
  10. astra

    astra Member

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    There is some difference.
    Consider that the barrel is a bit loose in the chassis hole. On the old LG110 the two screws are pressing on two flat pads that are made on the barrel and no arbitrary movements are possible. The Challenge has two sharpened screws that have a point contact on a rugged pads that allows quite arbitrary and non-repeating positioning of the barrel towards the chassis. And this could be very disapointing...
     
  11. hmangphilly

    hmangphilly Can't Re Member

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    Interesting
    I haven’t seen any flat pads on old barrels

    All my old barrels have a round circular surface.
    The barrel can be rotated 360 degrees and mounted in any position .
    Flat / cone tipped screws are typically used.

    Later barrels I’ve seen have cone point tipped screws that are expected to engage in conical recesses in the barrel .
    The recesses do not correspond exactly with the screws so the rifle builder can adjust one screw against the other to achieve a preferred lock up pressure.

    It is possible to to replace the 2 pointed screws with flat ones and rotate the barrel to tighten the screws agains a plain section of barrel .

    The barrel is not designed to be a snug fit in the chassis .

    At the bottom of the barrel hole is a a small Channel that creates clearance to the barrel
    This causes the barrel to sit againstthe edges of the channel ( like in a vee block )and when tightened from above ,the barrel is clamped at 3 contact points
     
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  12. hmangphilly

    hmangphilly Can't Re Member

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    Never seen a barrel like that Astra . Another variation to remember .

    I don’t have access to a chassis today
    But have a look just in front of the tp you might just notice a faint depression / channel

    Maybe yours is different in this respect which is why you can wobble the barrel when tight
     
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  13. astra

    astra Member

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    Yes, I have seen this depression in front of the TP but never noticed if it goes throw the entire barrel hole. Will check once at home just to make sure. Speaking for Challenge chassis I'm preapared for any kind of design surprises, after having widened the 3 barrel holes... experience that will never forget!
     
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  14. Simonix

    Simonix Member

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    My Challenge has had some strange going’s on with groupings recently.

    My barrel is held quite tight in the chassis. Held in place by all of the “a” frame parts.

    The front grub screw was left loose, result? - shotgun groupings with all pellets at anything beyond 30 yards.

    I tighten the front grub screw (just nipped up), and the grouping improves to a ragged hole at 55 yards!

    For whatever reason, my barrel likes being held in every place possible. I am concerned that if I were to “open” the chassis out and free float, my groupings would suffer.

    Never mind temp shift, I’m more worried about grouping full stop!
     
  15. astra

    astra Member

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    Oh, no!... ;) I played this many times -only the front screw, not understanding what's happening.
    You have to free the barrel from every point where it touches the chassis to let it float and vibrate freely like a bass string.
    Then the barrel becomes less stringent to pellets and bad series become good.
    Personal experience :)
     
  16. Simonix

    Simonix Member

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    But, if I machine and free float, I’ll end up with a “sloppy” barrel fit like you have said in your original post on this thread?!

    @chrisc what do you think? After seeing/servicing my gun last weekend?
     
  17. bootneckbob

    bootneckbob Active Member

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    "The front grub screw was left loose, result? - shotgun groupings with all pellets at anything beyond 30 yards.

    I tighten the front grub screw (just nipped up), and the grouping improves to a ragged hole at 55 yards!

    For whatever reason, my barrel likes being held in every place possible. I am concerned that if I were to “open” the chassis out and free float, my groupings would suffer."


    It's a tuning screw and what you are seeing is what it does! A pain in the arse it might be but I've had no trouble with mine. Once you know what and to use it there's no difference to setting up a stripper or the stock in general. Still some people will say free float so you pay's your money and take your chance!
     
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  18. astra

    astra Member

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    I was thinking exactly the same before I decided to open the chassis and free the barrel. What helped me in motivation to do so is ... just looked at the trusty old LG110 chassis, the Anshutz 9015 and many other match rifle chassis and you will get your answer very easily! Just mention whether do they have any touching point between barrel and chassis except the front 8, that is a subject of immediate freeing.
    And, if you were just in my climate zone you would not have had any doubts to free the barrel from chassis. Some world class shooters from England and Germany dicovered the temp change consequences attending the Eropean FT championship in Greece. Imagine shooting outdoors in 36-38 degs that is quite common here...
     
  19. blacklab

    blacklab Active Member

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    either way its a challenge sorry lads just had to;)
     
  20. astra

    astra Member

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    I checked the chassis hole, the depression is not visible but if you insert your small finger you could feel it well. I exchanged the cone shape screws with flat ones too and removed shimming cooper foil. The bass string sound now became a cello string i.e. higher pitched sound when knocked the front end of the barrel. Shooting with "good" series JSBs is still very accurate. Checked with some other series - still accurate, but needs some more trials to prove the setup is better than the shimmed barrel setup..
    Thanks to hmangphilly for suggestion!
     

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