Itching a scratch...

Discussion in 'Piston & Spring' started by RobF, Oct 4, 2019.

  1. RobF

    RobF Administrator Staff Member

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    We've had this in the grey matter storage for years but got around to testing it today.

    Previously we've moved away from seals as they appear to be quite unstable across temperature changes. We moved to o-rings which improved matters but recently I felt there could be more to be had. So after researching good and bad materials for temperature change we've finally found one which is about the same as aluminium and we can machine really nicely into a ring to fit exactly how we like.

    We didn't think it would be this simple but this is doing about 10 fps more than the o-ring at 760 fps on a 22mm 155g full skirted piston with about 1mm of preload and settled down instantly. A hint of Krtox on the piston and moly everywhere else. It's a long stroke because that's the flavour I prefer. It actually feels faster now though so I might slow it down some more.

    Few photos... the one with the high snatched shot is at 28 yards, and the other with 5 was at 55... i'll see what she's like over the next few weeks while I tweak the stock to fit betterer.

    WhatsApp Image 2019-10-04 at 19.20.19(1).jpeg WhatsApp Image 2019-10-04 at 19.20.19.jpeg WhatsApp Image 2019-10-04 at 19.20.18.jpeg
     
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  2. hmangphilly

    hmangphilly Can't Re Member

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    Didn’t think it would be long before he started inviting people to look at his ring
     
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  3. Adam

    Adam Well-Known Member

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    Intrigued by this wonder material. Unobtainium? :)
     
  4. dave croucher

    dave croucher FT, the sport where simple becomes complicated

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    Dunno about his ring ,bit Ive just bought his"used but not abused" tool
     
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  5. RobF

    RobF Administrator Staff Member

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    Carbon Peek CA30.
     
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  6. Nick G

    Nick G Active Member

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    Fascinating, I had settled on x ring as the most stable I have found . Your latest material may work well with my latest mad idea : I have knocked up four billet ally comp tubes ie one piece so no leaks in 21mm and had them hard anodized with ptfe in the finish , I have one in a gun working very well with a full skirted x ring piston doing 805 fps with express
     
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  7. hmangphilly

    hmangphilly Can't Re Member

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    You been having leaky comp tube probs Nick ?

    1 piece is a load of effort to go to .

    this piston ring worked much better than I expected.
    The first effort was in delrin just to see if it would work and get rough sizes .give one a try . It’s a straight drop in for an o ring . Just gotta remember how a piston ring works. We’re still in square at the moment but will prob try wedge shape in this piston soon

    I keep threatening to do a dykes head , I just know it’ll work
     
    Last edited: Oct 10, 2019 at 2:08 PM
  8. Nick G

    Nick G Active Member

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    not had leaks myself, but know of someone with a prosport who may be , I have drilled and tapped two of the tubes to suit, decided to do these tubes for ease of manufacture , and to scratch that itch .I also had a 21 mm reamer .Not tried a piston ring but have tried a delrin labyrinth, that made less fps and was too harsh for my liking , will give piston rings a try , how about two side by side and stagger the split , or is that not necessary with a diagonal joint.
     
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  9. Nick G

    Nick G Active Member

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  10. RobF

    RobF Administrator Staff Member

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    Nice... will the ally take the abuse?

    Yes, this is harsher but I think we know where to try next to soften that. If we go too far then it looks like this material is precise enough to tune it out.
     
  11. Nick G

    Nick G Active Member

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    The hard anodized finish is what it says , a file skids off , early days but it's looking good , and with an ally comp tube and piston it should all move at the same rate , for temp stability, not that I have noticed any with the x rings .
     
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  12. RobF

    RobF Administrator Staff Member

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  13. dave croucher

    dave croucher FT, the sport where simple becomes complicated

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    Further to this post, its smaller than I thought but beautifully formed and in lovely nick
     
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  14. RobF

    RobF Administrator Staff Member

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    yeh the metals aren’t a worry on temp, the plastics that most use for soft stuff have temp coefficients way in excess of metal, so they’re the culprit.

    Good stuff about the comp tubes. Are you going to do the pjc?
     
  15. Nick G

    Nick G Active Member

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    yes unfortunately missed it last year it's my favourites comp
     
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