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Ultimate Barrel.....

Discussion in 'General Airgun Chat' started by Bellerophon, Apr 14, 2018.

  1. tillygti6

    tillygti6 Tilly's gun stocks

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    so does that mean that for the above barrel , that over 50yards/150 feet the pellet spins 150 spins before hitting the target?
     
  2. tillygti6

    tillygti6 Tilly's gun stocks

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    so even a .22 at slower fps still does the same amount of spins?
     
  3. tillygti6

    tillygti6 Tilly's gun stocks

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    so a 1/14 twist gives the pellet doing 128.5 spins over 50yards. 1800 inches.

    so only 21.5 spins less ?
     
  4. hmangphilly

    hmangphilly Bit of a member

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    Thats how i see it Tommy .............at 1/12

    It will turn once for every foot travelled regardless of fps


    And 2/3 or 0.66 ish of a turn at 1/18 rate fill in the gaps for your favourite spin rate.

    the rpms are impressive though ..............no wonder some pellets start to wobble
     
    tillygti6 likes this.
  5. tillygti6

    tillygti6 Tilly's gun stocks

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    doesn't seem a big difference , or have I got it wrong? (probably)
     
  6. hmangphilly

    hmangphilly Bit of a member

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    I get the same number of turns Tommy .

    the fps will determine how long the pellet is in the air and therefore how long it takes the pellet to achieve that number of turns which we assume to be fixed

    say your 0.22 pellet is @ 600 fps against my 0.177 @800 with the (easy to calculate )1/12 twist ..............

    1 turn per foot
    600 fps = 600 turns per second

    it's only doing 150 feet so in the air for 1/4 second ......................?????

    oh my head is starting to hurt now
     
    Last edited: Apr 15, 2018
  7. tillygti6

    tillygti6 Tilly's gun stocks

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    ok, so it sort of makes sense that for each given twist rate, that there would be an optimum fps speed.

    given we know that the fac boys see problems with .177 at higher fps. could the slower twist rate allow for a higher fps?
     
  8. simona

    simona Active Member

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    In theory the perfect twist pitch varies with range. The greater the revs on the pellet the stronger its tendency to maintain its angle at launch. So at mega high spin the long axis of the pellet remains parallel to the ground. As the pellet drops it will start to present its sides to the direction of flight and drag goes through the roof.

    Rotation is lost at a lower rate that forward velocity so at long range the balance between spin and drag stabilization is lost.

    You don't want so much spin on the pellet at long range that the tail won't follow the head.
     
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  9. hmangphilly

    hmangphilly Bit of a member

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    This was suggested the other day .
    That the pellet does actually stay at the same angle during the whole of its flight .
     
  10. Slip Stream

    Slip Stream Experienced novice

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    In theory you are correct simona.
    But in practical terms the spin rate is governed more by the mass of the projectile, and the higher the mass the more kinetic energy it mantains in flight !?:rolleyes:
    Hence , long range rifles ( ref sniper rifle ) use 0. 460 calibre with a twist of only 1 in 30 , a couple I've used with smooth bore out to 2000 metre with good groups.

    Not a lot of research has been done on low mass sub 900 fps projectiles, that I've been able to find . Only a small amount by the great Ben Taylor whilst developing the smooth twist barrel now used by FX. who can supply any twist rate you require .

    From my own limited experience, a 12 or 14 twist gives a stable flight over the distances we shot. Which is the most commonly used by the airgun manufacturers .
    Maybe the new FX. barrels option will give us more data.
     
  11. simona

    simona Active Member

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    Out to 55 yards even 1 in 15 inch pitch airgun barrels group fine. Full bore stuff is very different as the drag stabilisation is not much of a factor.

    A 1 in 30 inch pitch airgun barrel might be better at 90 yards but not many people shoot at that distance with 12 ft lb guns.
     
  12. spiderman

    spiderman New Member

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    How much spin is too much spin?
    Too fast a twist rate and it's unstable, is there such thing as too slow a spin rate?
    There has to be an ideal spin/twist rate for an air rifle, 760-800fps is a small window compared to a centre fire velocities.
    Some of their rounds differe more than 1000fpd and bullets vary in weight of more than 100grn, most pellets differ in weight by less .5grn, re average being 8.5grn
     
  13. Rich3344

    Rich3344 Member

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    Interesting!

    What would the plan be regarding the choke?

    I wonder if the manufacturing process is repeatable enough to ensure you get all good barrels or if you'd have to batch test somehow, to select the better barrels.

    Failing that I'll have a 50m long smoothbore. That should sort out my grouping! :D


    We'd have to commission some ultimate pellets to go with it of course!
     
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  14. TenMetrePeter

    TenMetrePeter Member

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    Very interesting maths here. I guess the answer to your question is the rpm when centrifugal forces start to flare out the skirt like a rock n roll dancer!
     
  15. Sundance

    Sundance Member

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    When buying an Anschutz barrel for a .22LR you can pay extra to have a 'selected ' barrel. So I guess the implication is some are better than others straight out of the factory....
     
  16. chrisc

    chrisc Lucky git

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    I don't think we would be having this conversation if the Manufacturers QA was up to scratch?

    I know why the question was asked as when you’re bench rested it’s a bit frustrating that a 15mm group is difficult to get. Mechanical variations within the rifle, pellet variations and internal cleanliness can all conspire but if you KNOW the barrel is sound then there’s less elements to give the POI variations.
     
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