Reducing air volume

Discussion in 'Steyr' started by RichWafta, Nov 16, 2018.

  1. RobF

    RobF Administrator Staff Member

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    I think there is a misconception that if a gun has a large chamber it uses all that air, or needs to.
     
  2. hmangphilly

    hmangphilly Floppy Quick Phil

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    I think Ripleys do
     
  3. hmangphilly

    hmangphilly Floppy Quick Phil

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    But we had this ,
    Do you remember a walther set up that used so little air that we had to fire 3 shots to allow the reservoir volume to drop enough to allow the reg to cycle properly
     
  4. hmangphilly

    hmangphilly Floppy Quick Phil

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    Steyr reservoir = 15 ish cc ...............wow that's big .

    You could lose a chunk of that if you wanted Rich.

    your plug idea would work

    just had a measure with a syringe and olive oil sloshing around , could be 14 but its a ballpark .

    and im in trouble , i broke the missus saucer
     
    Last edited: Nov 17, 2018
  5. hmangphilly

    hmangphilly Floppy Quick Phil

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    walther domi 16 j reservoir approx 12cc

    if i remember the 7.5 j was around 7 or 8 cc
     
  6. RobF

    RobF Administrator Staff Member

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    And the anschutz we had was about 3...!
     
  7. NeilM

    NeilM Well-Known Member

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    The factory 9015 regs run around the mid to high 60's I believe. My reg was set up by JH at around 79 ish, if I remember correctly.

    My Mk1 EV2 when brand new had a very low shot count, the very early ones all did. Nick J and I messed about with ours, fitted much smaller diameter firing valves and removed the firing valve return spring and its plastic support. After doing that my EV gained 30fps and I had to turn the reg pressure down to get it anywhere near legal. I have never measured the plenum chamber volume in an Air Arms, but it is huge by comparison to the Anschutz and the Walther.

    Has anyone tried turning the reg pressure up in a Steyr? This will help slam the firing valve shut... to a point, after which you get into a fight between reg pressure and hammer spring pressure. It is the same method some Anschutz owners use to balance the reg against the hammer spring to help with temperature stability. Not a thing I have messed with, but I think Colin Eaton is a dab hand at this.
     
  8. RobF

    RobF Administrator Staff Member

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    If you count a 50 fps variation that is :D
     
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  9. Ratinator

    Ratinator 77.74

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    I'm hoping that the same will work for the Steyr. Only problem for me is the Plenum chamber, being oval, will be harder to reduce.
    You may well be right Cloverleaf and the efficiency may go the wrong way, but until I try.............?
    Now I need to look up this Boyles law o_O:confused:[/QUOTE]

    Does the volume reducer need to be oval ?
    Could you machine a ring that is a tight fit to drop inside the oval with maybe a couple of holes through the wall to include the part of the oval left ?
     
  10. MickyFinn

    MickyFinn I❤HFT

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    Hi Phil, its the 450mm version minus a little bit machined off the breech end.

    [​IMG]
     
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  11. hmangphilly

    hmangphilly Floppy Quick Phil

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    Nice Mick

    They still work well a bit shorter .

    I heard of a good shooter who had his cut super short to save from bashing it against trees and wotnot .

    :)
     
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  12. RichWafta

    RichWafta Second time around

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    Please pass on my apologies to Mrs hmangphilly for the broken saucer, but it was done in the name of science LOL.
    I am convinced I am on the right track with this. My initial idea of inserting a plug into the drill hole has hit a snag. I made it to be a push fit with an o-ring at the bottom to hold it in place. I took it apart again today and was surprised to find it had popped out of the hole. I'm thinking it must have had air below it and this blew it out when the gun was fired, the air pressure being slower to drop pressure below the o-ring seal I put it. I have replaced it, but with a 1mm drill hole going through, so hopefully this will get rid of the pressure.

    Reading your post gave me an "Eureka moment" Simon. Why does the plug I've fitted have to be the same depth as the drill hole? (which is what I did) If I make it the same length as the chamber, the end cap will hold it in place, plus I can then play around with different diameters of "plug" outside of the drill hole, thus giving me hours of pleasure trying to get the chamber volume to the point where I'm hopefully going to get a few extra shots AND a quieter firing cycle.

    Rob, I had a read of Boyles law. Couldn't see how it was relevant to what I am attempting to do though :confused:
     
  13. Ratinator

    Ratinator 77.74

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    Reading your post gave me an "Eureka moment" Simon.

    Hope it works out for you Richard , be interesting to here you results .
    I’ve had a “Eureka moment “ myself tonight.
    I’m going to make a jig out of kitchen worktop to enlarge the hole in my chassis where the barrel is tight, utilising the accessory slot in the bottom of the chassis
     
  14. RobF

    RobF Administrator Staff Member

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    What do the sums for a temperature variation of say 10 degrees with say 15 cc, and then 10cc's. What does it tell you?
     
  15. RichWafta

    RichWafta Second time around

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    It tells me that a given volume of air will increase in pressure if you reduce that volume. I am not reducing the chamber after it has been filled, the reg will still shut off at 86 bar whether it is filling 10 or 15 cc's and the volume of air would be 33% less. (I think)
     
  16. RobF

    RobF Administrator Staff Member

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    Work out the change in pressure for a fixed volume over a change of temperature, vs a smaller fixed volume.
     
  17. RichWafta

    RichWafta Second time around

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    Nah, I'm not clever enough. What do you think the result would be?
     
  18. hmangphilly

    hmangphilly Floppy Quick Phil

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    Is he on about Katie Boyle's law again ?

    Null points............

    katie boyle.jpg
     
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  19. RobF

    RobF Administrator Staff Member

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    Think of it like this.

    Temperature puts energy into a the air, yes? Like boiling a kettle puts energy into water. Does a kettle boil faster with less water in it or more? Same as the volume. If you have a smaller volume it's more subsceptible to temperature variation. We see it on the reg testers where we have small volumes, you can make the things shift up and down by bars by just holding them in your hand.

    Some guns have very small amounts of volume. Strange coincidence that one that has a teeny amount is also known to have shift issues.

    The amount of volume in the chamber does not dictate how much the gun will use. It will only use as much as it needs. It could have 200cc's behind it and it wouldn't use it all.

    The first reason the steyr's use lots of air is because of the choked transfer port. It's basically athsmatic. If that is open then the gun's valve doesn't need to be open as long to let the energy of the air get behind the pellet.

    Sorry for the red herring, it's not Boyle's law.
     
  20. Yorkshiretea

    Yorkshiretea B Grade Bandit

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    It's a long time since I've heard Boyles Law :) p V = C
     

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