TX200 short stroke piston - Mk1 or Mk2

Discussion in 'Air Arms' started by SDplinker, Mar 19, 2012.

  1. SDplinker

    SDplinker Pellet testing...yawn

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    Really want to shoot WFTF over here in the USA but I'd prefer a short stroke piston rather than using a weaker spring. All I can find is FAC Mk3 stuff as you can imagine. Thanks!

    Casey
     
  2. Recoiling Rob

    Recoiling Rob Member

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    Just change the rod, have one made 14mm longer

    Rob
     
  3. SDplinker

    SDplinker Pellet testing...yawn

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    I'm guessing it would cost me as much to do that as find a spare TX action? I assume the latching rod screws in somehow, that's how you can change it?
     
  4. Recoiling Rob

    Recoiling Rob Member

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    Rod is loctited in..

    Just remove the piston seal, heat the piston end and unscrew the latch rod.

    The difference from a Mk lll piston to a Mk l/ll is that the latch rod protrudes 14mm further out

    you will need a Mk l / ll spring top hat and guide to complete the transformation though as the MK lll spring etc. is a larger internal diameter with thiner wire

    Rob
     
  5. SDplinker

    SDplinker Pellet testing...yawn

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    Thanks Rob

    Spoke to a machinist who has done a couple things for me. He hasn't done a TX latch rod before but has done them for a number of the HW rifles when he made custom pistons. The price he quoted for the TX didn't sound bad at all so I'm going to consider going this route. In fact he thought it might be easier since the TX latch has a uniform profile all the way around.

    Anything to watch for regarding the material or the tolerances?

    Thanks!

    -Casey
     
  6. Recoiling Rob

    Recoiling Rob Member

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    Hi Casey,

    I had some done and had the "latch" end case hardened, they are still going strong

    cheers

    Rob
     
  7. SDplinker

    SDplinker Pellet testing...yawn

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    Good to know Rob, thank you. I'm sending my spare compression tube and piston off later this week for a test conversion. The machinist also does O-ring conversions and they tend to pick up some speed (15-30fps) over the standard seals. So it will be a balance of stem length and spring to achieve 12fpe. I do think going with the longer stroke will be best. I've heard of Mk2 pistons being about 1.4" in length at the stem and the Mk1 approximately 1.75". My current Mk3 is 1.25".

    One concern I have is the anti-beartrap mechanism - not sure if it will lock up all the way on the 3rd notch with the shorter stroke. But I suppose there are still the other 2 notches plus I never ever let go of the cocking arm.

    I'll post some results here when the work is done and I have tested it out. Guys in my club have been getting good results with the O-ring modification - no temperature induced POI shifts any more.

    -Casey
     
  8. Recoiling Rob

    Recoiling Rob Member

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    Nice one Casey,

    The Mk1 and MK ll pistons are exactly the same, there is a slight difference on the compression tube, but its only where the cocking shoe fits...

    I'll be interested to know about the O ring seals, I would have thought that it will allow metal to metal contact at the end of the stroke?

    Please post how you get on

    Rob
     
  9. Recoiling Rob

    Recoiling Rob Member

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  10. SDplinker

    SDplinker Pellet testing...yawn

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    Here's a picture of my recently converted piston. This is using moly-filled nylon as the head material. He has also used aluminum. I may have him convert mine to aluminum as well since he has discovered some expansion under certain circumstances with the nylon and it swells a bit if you end up dry-firing (all in the name of testing of course) :)

    At least in the case of the nylon, no metal to metal. And even with the aluminum it seems to work great. He's done this on R9/HW77 pistons for years and it's worked wonderfully. Consumable costs are considerably less too since mil-spec Viton o-rings are tons cheaper than that standard seals. I think I just bought 50 of them for about $7 US.

    [​IMG]

    [​IMG]
     
  11. SDplinker

    SDplinker Pellet testing...yawn

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    Also to note - the conversion is reversible. The cap is held on with nylon set screws of some fashion. You could remove the whole thing and go back to regular seals. The piston itself is not altered.
     
  12. SDplinker

    SDplinker Pellet testing...yawn

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    The test piston is with the machinist for modification. The plan is to replace the factory Mk3 stem (1.25" length) with a Mk1 or thereabouts spec of 1.75" length. He is also modifying the piston head to convert it to O-ring sealing as opposed to the factory seal.

    When I get it back I'll use a variety of spring/guide/tophat variations to see what power level it shoots at. The O-ring mod usually adds some speed so some refinement may be needed.

    -Casey
     
  13. SDplinker

    SDplinker Pellet testing...yawn

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    Short stroked piston should arrive today. Hope to have some information, thoughts and data soon. Plan initially is to do a direct swap with current setup (same spring, action) and pellets and see how velocity/shot cycle is affected. Pics below of how it turned out.

    [​IMG]

    [​IMG]
     
    Last edited: Apr 5, 2012
  14. SDplinker

    SDplinker Pellet testing...yawn

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    Short stroke piston now installed

    Here's where we stand now. Have 2 TX200 actions. One of them is now sub 12fpe. Both came to me in FAC trim. TX200 #1 is left-hand action in a right hand stock. It was shooting JSB8.4g at 885fps. This was post-O-ring piston conversion. TX200 #2 is action only. The guy sold it cheap saying that it didn't work. I figured only so many things can really break and was able to fix it with a reseal and a trigger cleanup. It is right-handed and also has an O-ring piston. #2 also has a longer cocking rod made by Ed Canoles (EC). I had him do this so I could have a true short stroke TX like the Mk1's. TX #1 has a slightly longer spring, #2 is a bit shorter but has same number of coils. Summary of results to date below:

    Long stroke standard Mk3 piston with the longer spring and 8.4JSB - 885fps
    Short stroke EC piston with longer spring and 7.9JSB - 790fps
    Short stroke EC piston with shorter spring and 7.9JSB - 675fps
    Short stroke EC piston with shorter spring and 7.9CPL - 620fps (CPLs are tight so that's all that can account for that)

    Both guns were previously tuned but with standard parachute seals - I became enamored of the O-ring conversion after several guys at our club reported that it eliminated POI shifts due to temperature of the action/lubes. Figured I'd give it a go. It does speed the guns up a bit though. Nice thing too is that O-rings are dirt to cheap to replace - a lifetime supply is about $10. It's all reversible if I ever change my mind which is cool.

    I plan to add a washer or two to get the rifle shooting 7.9 at about 800fps. Or I just maybe leave it where it's at - too be determined after more shooting and range time.
     
  15. SDplinker

    SDplinker Pellet testing...yawn

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    Shot the first match with the short stroke

    The gun seemed to shoot quite well. It was very unique venue - lots of very long and very uphill shots with 10-15mph wind gusts. My score was terrible but it wasn't the rifle. Just a new springer shooter figuring out the wind and the clicks.

    The match was held at the home of one of our most esteemed airgunners and he has a 51 yard tunnel buried next to his house. You can sit down in a little room and hang targets at the other end and test your gun in still conditions. Great for accuracy tuning and pellet testing. Once I got the hang of the TX on the tackdriver bag, it was an inch or less at 51 yards so the rifle is accurate.

    An experienced TX shooter at the match tried the gun and felt that a softer cocking spring could be used an still achieve the 12fpe that I desire. So now I'm investigating options - V-Mach, Maccari, Vortek etc. If any of you have had good success with any particular kit in a Mk1 stroked rifle please let me know. Thanks!

    Casey
     

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