Preferred muzzle energy/pellet speed

Discussion in 'Piston & Spring' started by Cooper_dan, Jul 3, 2018.

  1. hmangphilly

    hmangphilly Can't Re Member

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    Can any one talk me through this in language suitable for a stoopid person ?

    I'm struggling with the piston displacement thing particularly.


    Im thinking it would depend on how the muzzle velocity is reduced as to how much effect it has on shot cycle
     
  2. Nomads HFT

    Nomads HFT Well-Known Member

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    Dan reduced spring preload to lower muzzle energy, Phil, so the piston receives less energy and does not travel quite as far up the cylinder. The term 'displacement' refers to the distance the piston travels during the compression stroke.
     
  3. Nomads HFT

    Nomads HFT Well-Known Member

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    Thanks for the offer, Dan. When my (steel clad) workshop cools down enough to support human life I've got a lot lined up, so perhaps later in the year?

    The recoil/surge displacement will reduce pro rata as the rifle/stock/scope mass increases.
     
  4. Adam

    Adam Well-Known Member

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    Do you mean the piston does not travel as far up the cylinder before it bounces back, so surge starts at an earlier point in the stroke? Is this earlier in time (i.e the average piston velocity is about the same but the the distance is shorter) or the same time (the velocity is lower)? To what degree does this affect the overall "lock time"?

    Yes I know chasing lock time is pointless and we should concentrate on follow through yada yada. I'm just interested, primarily in the reason why since adding about 2mm of preload to my LGU (3mm port, otherwise standard) resulted in less perceived sight picture movement, but slightly more hold sensitivity.
     
  5. Nomads HFT

    Nomads HFT Well-Known Member

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    I have not directly measured lock time with regard to preload, Adam, but feel the effect will be miniscule. The piston travels a fraction of a mm nearer the end wall if preload is increased, but the preload gets it there a touch sooner, and vice versa, so it probably evens out.
     
  6. Finners1960

    Finners1960 Member

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    Very interesting thread and one that I hope will help my battle with my lgu.
    The only modification I’ve made is to open the tp to 3.2mm. After doing this, I was getting a definite ‘twang’, which wasn’t noticeable before. I’ve put in a piston sleeve, which calmed it down, but it dropped the muzzle energy to 10.0 ft/lbs with 7.9grn Express.
    I’m now finding increased hold sensitivity, even though it is in a full on laminate FT stock!
    I’m not sure where to go now, but I’m going to try increasing the preload with a piston washer and one on the spring guide too. I’m hoping that this will bring up the energy to 10.5ft/lbs, which to answer the original thread, is where I find all my springers like to be.
    Any thoughts on my remedial plan? One washer at each end, or just on the guide??
    Your thoughts?
    Finners.
     
  7. Finners1960

    Finners1960 Member

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    ...forgot to add, I collapsed a coil on the spring after opening the tp.
     
  8. Nomads HFT

    Nomads HFT Well-Known Member

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    What was the muzzle energy before you fitted the piston sleeve, Jez?
     
  9. hmangphilly

    hmangphilly Can't Re Member

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    Get rid of the sleeve . It is clearly too tight .

    Why did you feel the need to collapse the coil ?

    If I remember , the std lgu has no bottom ( :) ) guide / top hat leaving the spring free to wobble about inside the horribly rough piston skirt .

    Space may be an issue if you are thinking of adding lower support , it is possible that the main guide will need shortening to accomodate a lower top hat /guide .
     
  10. biwain

    biwain Tree bark and paint chipper Champion

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    Why this obsession with chrono reading's and muzzle energy.

    If you can hit a target at 55yard's and it feel's nice, why keep preloading the spring.

    Men seem obsessed with measuring thing's and are alway's disapointed from the age of eleven.

    The more load you put on the trigger, the more inconsistent it becomes the heavier you need to set it.

    I have no follow through above 12oz so I have to set my action to the trigger regardless of output.
     
    Gary Martin and hmangphilly like this.
  11. Nomads HFT

    Nomads HFT Well-Known Member

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    That's the most plausible explanation, Phil, though not the only one, which is why I asked the question.

    If the spring IS binding in the piston sleeve then, at piston release, the spring will start to extend from the wrong end (the rear), so it is not only pushing the 250g of piston, but also much of its own 125g mass, increasing recoil displacement and explaining the hold sensitivity that Jez reported.
     
  12. Adam

    Adam Well-Known Member

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    What scope have you got on it Jez? Wondering about overall balance of the rig being a factor. I need to check my rig’s balance as mine is also in a laminate FT stock.
    Also it’s likely that the new stock has changed your hold.
     
  13. Finners1960

    Finners1960 Member

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    Hi guys, thanks for your thoughts. To answer your question Jim, after opening the tp, it was running around 11.5 ft. Lbs. I prefer my springers around 10.5... hence why I shortened the spring. The sleeve is 0.25mm ptfe, which I’ve used before to good effect. I hadn’t considered that it may be causing the spring to bind when compressed, but it now seems plausible!
    I’ll check it tomorrow.
    Adam, I’ve got a leupold 20/50 on top. Not sure how this will effect the hold sensitivity??
    I’ll examine the ptfe sleeve tomorrow for signs of the compressed spring impacting on it.
    Thanks again guys.
    Jez.
     
  14. Nomads HFT

    Nomads HFT Well-Known Member

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    If the PTFE sleeve is not causing the spring to bind, I'd try adding a 3mm preload washer at the rear of the spring to get to ~10.5 ft. lb., Jez.
     
  15. Conor

    Conor Never been banned from sales Staff Member

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    So what is the preferred muzzle energy for a twanger? Under 11ft/lb?
     
  16. hmangphilly

    hmangphilly Can't Re Member

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    Are these guns still knackering springs out ?
     
  17. hmangphilly

    hmangphilly Can't Re Member

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    Depends who you ask Con.

    looks like Brian and John are happy around 10 .5 , but I heard Doz likes them right up the top end ............


    One mans meat .......etc..........
     
  18. Brian.Samson

    Brian.Samson Allowed in Sales Staff Member

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    Does it matter? I don't think your final score has much to do with your muzzle energy personally.

    I put in a 45 at Bisley doing 739 fps with 8.4's. Apparently it was a long course with 17 targets beyond 45m so you'd think 10fpe would be disastrous wouldn't you?

    Practice and a heavy stock - those are my top tips.
     
  19. Nomads HFT

    Nomads HFT Well-Known Member

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    I don't know, Phil. My LGU and LGV both now have Mk.3 TX200 springs.
     
  20. biwain

    biwain Tree bark and paint chipper Champion

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    Doesn't matter what your guns doing, give it to Brian or Steve or John (not to mention any names) and a pound to a bag of poop it will come back with a good score.
     

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