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TX200 stroke length common misconceptions - anyone actually measured it?

Discussion in 'Anything Airgun Related' started by cloverleaf, Oct 16, 2013.

  1. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    If you ask the internetz or anyone who professes to know about such things, everyone will tell you that the Mk1/2 TX200 has a stroke length of 86mm and the Mk3 has a longer 100mm stroke. I've regurgitated these two figures to many, many people, but have never actually measured them :eek:

    Today the Mk2 and Mk3 were relieved of their stocks and prodded with the ruler. With the rifle uncocked a piece of clear tape with a Tippex marker on it was placed on the cylinder, level with the rear of the piston skirt. The rifle was then cocked and the distance between the marker and the rear of the piston skirt measured:


    Mk2, uncocked showing marker:

    [​IMG]


    Mk2, cocked, with ruler to illustrate stroke length:

    [​IMG]


    Mk2, cocked, closeup of the ruler & piston:

    [​IMG]


    Mk3, uncocked showing marker:

    [​IMG]


    Mk3, cocked, with ruler to illustrate stroke length:

    [​IMG]


    Mk3, cocked, closeup of the ruler & piston:

    [​IMG]


    From the above it certainly appears that the actual strokes are a little shorter (4mm) than is widely accepted - the Mk2 stroke being 82mm as opposed to 86, and the Mk3 stroke being 96mm as opposed to 100.

    If you're a casual TX user this will mean absolutely nothing to you, but for those tinkering with stroke length (especially those too lazy to measure anything, like myself :rolleyes:) this is important. For example I based my short-stroked piston on the dims of the original at a stroke at 100mm, so my setup is actually shorter than the 70mm I'd intended (actually 67.5mm so I must have cocked something else up too). It probably goes some way to explaining why it won't make much muzzle energy..

    Obviously I'm flying in the face of most other sources so please feel free to suggest ways I might have cocked up the measuring process, but I think it's pretty idiot-proof tbh :p

    Anyone else found similar / different / want to measure their TX?
     
    Last edited: Sep 24, 2019
  2. Jackal

    Jackal Posting Addict

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    I concur...so which is best?
     
    Last edited: Oct 16, 2013
  3. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    Not this again... :p

    So far I've found that the shot development time (elapsed time between trigger release and pellet exit at muzzle) is around 12-12.5ms for the Mk2 and anything between 14.5 and 17ms for the Mk3 (having trouble measuring it - probably more likely to be towards the lower value). A faster SDT will make the rifle easier to shoot unsupported, so this goes in the Mk2's favour (I found this to be the case when they were tested back to back freestanding).

    I'm getting good efficiency figures from both guns (38-41%) with the Mk3 being slightly better; although the spring rates are calculated rather than measured so the potential margin of error on these values makes the difference insignificant atm. I need to build a spring rate tester to know for sure, so the jury's currently out on this one.

    It's subjective but I prefer the faster shot cycle of the Mk2.

    I can't comment definitively on hold sensitivity - the Mk2 does seem better though.

    The Mk3 has a lower cocking effort.

    Off the bench the Mk3 is very good; not had a whole lot of chance to test the Mk2 yet.
     
  4. valboskie

    valboskie Busy Member

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    Intersting reading mate.
    Im sure bigtoe added a 14mm longer piston rod and 10mm of preload to his tx200mk3
    To get it to shoot like a mk1.
    18mm longer rod is the best but the bear trap does not work but it shoots the sweetest.
     
  5. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    Thanks :)

    Yes, I read Bigtoe's blog too (needs an update ;p); so based on my measurements that would give his -18mm conversion a 78mm stroke. A pity it doesn't work with the anti-beartrap..
     
  6. valboskie

    valboskie Busy Member

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    Niel180 has played around with stroke as well he has a few you tube videos under tracie birkin.
    He tried a 14mm nose extension on the piston plus the longer piston rod.
    The longer rod produced the best results for him.
     
  7. Akita177

    Akita177 Sharpen the pikes

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    You could PM Uk Niel on the other forum.
    He made me a 14mm piston spacer which appears correct for your measurments 96mm minus 82mm equals 14mm.
     
  8. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    Thanks - I've already got a short stroke setup on the go courtesy of a modified longer rod (although it needs a little revision). The purpose of the post was really to share the stroke measurements since many tinkerers (myself included) seem to accept the apparently wrong values of 100 and 86mm :)
     
  9. imorik

    imorik Busy Member

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    An interesting article in Septembers Airgun World on this subject. Jim Tyler fitted a piston extension to his 77 to short stroke it, felt better to shoot but turned out to be far less accurate. Something to do with shifting the pellet barrel timer out of the consistant recoil cycle (barrel moves upwards) more into the inconsistant surge cycle (barrels moves downwards). The article suggests that an accuracy test should be done before and after any tinkering to check the effectiveness rather than what it feels like to shoot. I'm no expert but must admit to being a tinkerer and have tended to go by how it feels to shoot without checking accuracy before and after.
     
    Last edited: Oct 17, 2013
  10. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    Thanks - I've discussed this with Jim and I agree that as usual not everything conveiniently falls into place; setups that may offer optimum shot cycle feel may not offer the best efficiency or accuracy..

    It's funny that this article about pellet exit timing came out just after I'd started chasing efficiency figures with my short-stroked TX200. I'd assumed (albeit with a healthy cynicism) that an efficient gun would be an accurate gun. Jim's article could have been written as a direct rebuttle of this assumption :p

    I'm very interested to test some of Jim's thoughts and findings for myself; although unfortunately I don't have the means to do so (other than with actual accuracy testing, which leaves the process open to all manner of other changing variables too).

    So it appears that we have maybe four output variables to consider when tuning an air rifle:

    - Shot cycle feel (how pleasant the firing cycle is - vibrations, acceleration, velocity and total displacement of the rifle)
    - Hold sensitivity (POI change with changing restraints on the rifle)
    - Shot development time (the elapsed time between trigger release and pellet exit)
    - Pellet exit timing (the point at which the pellet leaves the muzzle with respect to the velocity of the muzzle in a direction perpendicular to the bore)

    Of these, the first is largely subjective and will have no real bearing on accuracy (other than psychologically). The second and third will make a big difference to how accurate the gun is during field conditions, and the fourth will directly influence how the rifle performs from a rest, when all other human factors are removed.

    Obviously it would be nice to find a state of tune that satisfies all four of these criteria; in reality while some optimised variables will work well together to mutually improve more than one, to satisfy them all will probably require a compromise somewhere..
     
  11. bigtoe

    bigtoe Donator

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    he short stroked the 77 to much, I told him so also

    tx and 77 stroke rules

    .177 75 to 83mm
    .22 70 to 73mm
    .20 73 to 77mm
    .25 75 to 83mm

    Jim went to 70mm on the 77, to fast and probably slammy, especially if he was still using a 4mm TP.
     
  12. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    Images sorted...
     

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