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TX 200 light weight piston ( opinions)

Discussion in 'Anything Airgun Related' started by Nickg, Jan 1, 2014.

  1. Nickg

    Nickg Busy Member

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    Hi There, and a Happy New year to everyone. I have been shooting my mildly tuned TX MK3 for about a year now ( 10 mm piston ext, vortek, o ring, polished sears) and have been very happy with it. However after reading every post on the subject that I could find ,I decided to do something more radical,: an extremely lightweight piston, I have made a new 'o'ring piston which is extremely short, ie no skirt' about 24mm long this has an extension at the rear which does three things ,extends the length of the latch rod, locates the spring, and adds some weight. This has a synthetic bearing at the rear similar to the original. A synthetic rear guide gives the latch rod some support and locates the spring. The spec is a as follows:

    Piston weight 177gr
    Stroke 83mm
    MK 2 Titan XS spring
    Standard transfer port

    After settling it in with fifty or so shots, I took it to the range ( Greyhound ) The shot cycle is very quick and it seems less hold sensitive than before ( which is what I am trying to achieve), The problem is I don't know how to tell if it is bouncing or not, I have Chronoed it with three pellet types:

    JSB Exacts 8.44gr 769fps 11.02 ft lb It seems to like these hardly any movement in the sight picture
    Falcon 7.33gr 839fps 11.47 ft lb Does not like these, more movement in the sight picture
    RWS Superdomes 8.4gr 740fps 10.09 ft lb Haven't had a chance to shoot these yet

    I think it may be slamming with the lighter pellets, and the super domes may be a bit tighter in the barrel giving the lower speed , but I am only guessing,

    If it is bouncing I want to try a different size transfer port, but only if it is bouncing so Ideas please.

    My original thoughts were to fit a longer softer spring a la Jim Tyler ,but could not obtain one. However had a bit of luck as I gave the gun to a gentleman by the name of Jed Clampit to try, and he has one of Mr Tylers TX 's that he will bring this coming Sat, so we can compare the different shot cycles side by side , should be very interesting.

    Sorry for the long post wanted to get all the info down.

    Oh every one that has shot this seems to like it:) , so hopefully going down the right track.
     
  2. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    An interesting post - thanks for sharing :)

    I too have considered binning the piston skirt to reduce mass. What sort of piston seal are you running now? Tbh I'm struggling to visualise your setup; any chance of some pics please? :D

    So compared to the standard (225g) Mk3 piston, your 177g item has saved around 48g / 21%, or (taking into account the horrendously heavy .177 piston weight at around Mk3 39g) more like 88g / 33% of total piston mass.

    Since your setup is far closer to the 82mm stroke of the Mk2; doing a similar comparison gives a mass saving of 55g / 24%, or 83g / 32% over the standard Mk2 .177 setup.

    Either way a substantial saving over stock. A couple of things spring to mind; it's generally accepted that for a given pellet, spring spec, piston stroke and energy output there's an ideal piston mass where peak system efficiency is reached. From an effiiciency perspective, I've only ever had good experiences with lightening existing TX setups (standard, but with shorter / lighter top hats or synthetic alternatives) however it figures that this can only go so far before efficiency begins to fall.

    To this end, if you can provide me with a few specs (spring wire dia, spring OD, total no. coils, feel length) plus spring preload, I can do some efficiency calcs.

    Another few points I found of interest were that a) there was such a marked difference in muzzle energy output between different pellets, and b) that you liked the most efficient pellet the least. I take on board your suggestion of the worse firing manners being caused by "piston slam" a terms that's oft-banded about, however tbh without and sufficient measuring gear to confirm that this is going on, pretty difficult to confirm IMO.

    Anyway, certainly interested to hear more :)
     
  3. Nickg

    Nickg Busy Member

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    I am using an "O" Ring, situated right at the front of the piston to minimise any lost volume. I have also posted this on the other forum, and a John Budd has responded suggesting that the reason for the difference in muzzle energy for the different weight of pellets indicates bounce. To this end I am going to make a couple of adjustments to try to optimise the stroke, so will take some photo's when its down and measure the spring. I read some of your earlier posts using audacity to measure shot cycle, and actually did this with the TX in an earlier state of tune, so may do it again to see the difference. Thanks for showing an interest.
     
  4. Nickg

    Nickg Busy Member

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    I measured the spring, and the specs are now, Spring od 20.7, coil gauge 3mm, active coils 20, coils per 25mm 3, free length 220mm, preload 19mm, The piston now weighs 179 grams, and the stroke is 80mm.
    I have tested with two pellet weights, JSB @ 8.44gr 755 fps 10.62 ft lb, Falcon @ 7.33gr 814 fps 10.74 ft lb. Will try to get some pics of the piston up later.
     
  5. Nickg

    Nickg Busy Member

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    Piston Pics

    006 (640x480).jpg 004 (640x480).jpg
     
  6. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    Thanks, and apologies for my late reply :)

    That certainly looks very interesting; plugging the figures into my magical spreadsheet gives efficiency figures of 42.6 and 43% for the Exacts and FAPs respectively; which is very good in my experience (my standard .177 Mk2 gives around 38% and my standard-stike Mk3 gives around 41% - some of the best .177s I've tested).

    I'd be interested to see how the lighter piston affects shot development time and if the efficiency remains as high were a few mainspring spacers added to increase pre-load and push the energy up a bit nearer 11.5ftlb.

    I was thinking about the ratio between spring and piston mass - as the piston comes to a halt at the beginning of bounce, a significant amount of the spring's mass should still be travelling forwards under it's own inertia; potentially providing additional force and a damping effect on the bouncing piston. This might be of benefit for improving efficiency, performance and manners; through effectively increasing piston "dwell". Would be an interesting experiment to try; along with the many others I've never got around to :eek:
     
  7. Nickg

    Nickg Busy Member

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    Thanks for the reply, The gun is very easy to shoot accurately now, as an example I gave it to a friend who owns a pro sport, I dialled the scope for our furthest knock down targets 63yds. He accepted it with the comment " I have trouble hitting these" then hit the first two, missed the third and hit the fourth. Having never shot it before !. I will try a little extra pre load when I have the time, and see if I can get the dwell down a bit further.
     
  8. Akita177

    Akita177 The Absolute State of Britian podcast

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    Interesting mate, i will have to bring my standard one and compare them next time we shoot.
    Im getting over this chest infection now so to go do some practice soon, a bit depressed about missing Dowry Hill matey.
     
  9. Nickg

    Nickg Busy Member

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    You will love the TX, It was john with the pro sport who tried it, his has a standard stroke, yours I believe has a 14mm piston ext so will be good to compare. Dowry hill was a nice course and I was paired up with Strokebloke so it was fun. Did not shoot as well as I have before though, so hopefully better next time. Glad to hear your on the mend, Purley this Sunday ?.
     
  10. walker

    walker Busy Member

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    were you at the greyhound on saturday. shooting with an old boy who had a nickel 97? or am i just talking rubbish lol
     
  11. Akita177

    Akita177 The Absolute State of Britian podcast

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    If purleys on i will be there mate, its the correct weekend for it so i hope its on.
     
  12. Nickg

    Nickg Busy Member

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    I think so , I spoke to Alan at Dowry and he said it was.
     

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