Inconsistant TX200.

Discussion in 'Piston & Spring' started by zooma, Mar 14, 2020.

  1. Nick G

    Nick G Active Member

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    Check your power over the chrono , piston takes around ten shots to rotate once if your power is varying up and down consistently over ten shots then coming back to where it was on shot one , your piston rod is running out and getting tight and loose as in the trigger block or guide as it rotates.
     
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  2. zooma

    zooma Member

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    Really helpful video - I will check this today!
     
  3. zooma

    zooma Member

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    Thanks - I will check this and see what is happening.
     
  4. zooma

    zooma Member

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    I have ordered a Mk 2 piston as I wanted to try one anyway because of all the good things I have heard about fitting this with a new standard Air Arms main spring.

    Hopefully this will also help this particular TX200 cock and set the safety reliably - which in turn may solve the inconsistent grouping?
     
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  5. Nick G

    Nick G Active Member

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    You will need a mark 2 spring to suit and the guide altering, also check the new piston rod for run out as some are bent , or not fitted concentrically from new .
     
  6. Cooper_dan

    Cooper_dan Well-Known Member

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    Not true. Mk2 piston, with MK3 spring and guide works perfectly. Around 42mm preload for a .177 gives 770 ish FPS with 8.4g
     
  7. Cooper_dan

    Cooper_dan Well-Known Member

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    This is a proven good setup. Last year's UKAHFT recoil championship at Nomads, top 3 shooters were using TX200's with this setup or very close to it.
     
  8. Nomads HFT

    Nomads HFT Well-Known Member

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    Of which two had Mk.3 springs, and I am given to understand that the third has now seen the light and switched to a Mk.3 spring. :cool:
     
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  9. Cooper_dan

    Cooper_dan Well-Known Member

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    My mistake, I thought all 3 were on MK3 springs at the time.
    My spring has been in for almost a year now and has lost a total of 2mm length in that time. Very very happy with how it shoots and the reliability. I only have to strip it down when I use it in the pouring rain and need to dry it out.
     
  10. Nomads HFT

    Nomads HFT Well-Known Member

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    Then it was my mistake; you hadn't told me you'd gone Mk.3 spring before the event, Dan.

    So it was top three, all circa 85mm available stroke, Mk.3 springs, 41mm of preload.
     
  11. Cooper_dan

    Cooper_dan Well-Known Member

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    I'm starting to doubt myself now :oops: Isolation is turning my brain to mush.
    That was either the very last competition I used a mk2 spring, or the first time I used the mk3.
     
  12. zooma

    zooma Member

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    Still a good bit of advice that I am happy to take and try for myself!

    Mk 2 piston and Mk 3 spring.......but I will check for a dodgy piston rod, but hope mine is OK when it comes!

    Thanks Dan!
     
  13. FPoole

    FPoole Active Member

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    Is this Mark3 spring the 12 ft. lb. one or the FAC Mark3 spring?
     
  14. Nomads HFT

    Nomads HFT Well-Known Member

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    It's the UK 12 ft. lb. spec spring; 20.8mm OD, 2.9mm wire, 23 active coils, 5.27 N/mm.
     
  15. Nick G

    Nick G Active Member

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    I realized the mk 3 would work with plenty of pre load thought the op was unsure as to mk 2 spec , interesting using the mk 3 spring, makes sense if you lose the big MK2 piston weight the extra preload needed will also control the bounce , are they any easier to cock ? As the extra pre load will surely make up for the lower spring rate over the heavier mk 2 spring , just interested as I have my own guns set up differently.
     
  16. FPoole

    FPoole Active Member

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    Thanks for the reply. I never thought the little 12 ft. lb. spring would be enough to power a Mark1 stroke gun. I've got one around somewhere, now have to remember where I put it.
     
  17. Cooper_dan

    Cooper_dan Well-Known Member

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    Cocking is marginally easier, but you would need compare back to back with a MK2 spring to really notice the difference. It's not different enough to be the main benefit.
    The extra preload definitely controls bounce. With my MK2 setup, losing the piston weight lost about 2% measured efficiency. Going to MK3 spring gained thas 2% back again. So just as efficient but lighter piston.

    With the MK3 spring I also see more pellets into the target than before. On a good day I can shoot 45y targets and watch every pellet in. But tbh that's probably 90% down to the stock, but the softer spring has made a positive difference too.
     
  18. Nomads HFT

    Nomads HFT Well-Known Member

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    Easy enough to calculate, Dan, if we know the Mk.2 spring rate, and the preload needed for equivalent muzzle energy.

    Mk.3 spring, 85mm stroke, 41mm preload gives 663.78 Newtons (149.22 lbf) acting on the piston at the point of release.

    The figures I have (if they're correct) would place the force on the piston at 738.38N (166 lbf) for the Mk.2 spring even with zero preload, so 11% higher cocking force, but that rises to 808N (181 lbf) with preload to deliver equivalent energy to the piston.

    You're quite right it's not the main benefit.
     
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  19. Nick G

    Nick G Active Member

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    So given the mk 3 is making 30 ft lb less than the MK2 spring available to the piston , and the piston is lighter virtue of leaving the piston weight out , how is it making the same power ( at the same stroke ,)
     
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  20. Cooper_dan

    Cooper_dan Well-Known Member

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    It's the average spring load applied to the piston over the full stroke that will determine how much energy is available to the pellet.
    My numbers are slightly different to Jim's but I've got the load on the spring in the fitted condition and the cocked condition for a mk3 and a mk2 spring, both with a mk2 piston stroke, both making exactly the same muzzle energy, both with the same efficiency**

    Screenshot 2020-03-27 at 18.00.18.png

    Because both setups are the same efficiency** the average amount of force on the piston throughout its stroke is the same. In this case 463N.
    The left side of the graph is the un-cocked position, the right side is the cocked condition.
    The mk2 spring with higher spring rate (stiffer) has lower pre-load (120N), so to get an average of 463N, the spring load needs to be increased to 798N
    The mk3 spring with lower spring rate (softer) has higher pre-load (230N), so to get an average of 463N, the spring load needs to be increased to 697N.
    The trend lines increase at different rates, proportional to the spring rate.

    When cocking the mk2 spring setup, you are manually adding 678N.
    When cocking the mk3 spring setup, you are manually adding 467N.
    So actually the mk3 spring setup requires the shooter to add 30% less load to the spring when cocking. But I think the leverage and possibly technique makes this feel less to me.

    **Efficiency - When the piston has been released and has reached end of stroke, the mk2 setup only has 120N pre-load to resist bounce. The mk3 spring setup has 230N pre-load to resist bounce (almost double). So with identical piston weight, the mk3 spring setup is more efficient. The big mk2 piston weight adds to the efficiency of the mk2 spring setup, and they end up similar.

    Long soft springs rule!
     

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