Drop in power

Discussion in 'General Airgun Chat' started by mak1, Feb 2, 2019.

  1. RobF

    RobF Administrator Staff Member

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    Odd because we aren’t seeing that. If we let a reg sit then it just obeys the ideal gas laws as temps change. The pressure goes down when it’s cold and up when it’s hot. If the reg is perfectly sealing then the tester is just monitoring a fixed volume. If the pressure drop below the set presage in the regged volume the reg should open up again to fill it.

    I know you know this but this is for others. The reg works by adding the force from the regged chamber against the spring force to balance the force on the valve from the inlet pressure. Some work by using the inlet pressure to close a valve with the inlet pressure, some against it.

    If we say the cold is reducing the inlet pressure then that is just the same as shooting more shots off and lowering it anyway. So we know it’s not that.

    If we say it’s affecting the sealed off reg chamber and dropping that then the reg should open again and let more pressure in to balance it, like it would do if there was a small leak on the regged side. So it’s not that either.

    That’s my thoughts.

    I’m not convinced it’s anything to do with the reg. As a guess I think it’s just the air has less energy at lower temps.

    I haven’t got any non regged guns but if they do it then that rules the reg out.
     
    Last edited: Feb 6, 2019
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  2. C.Eaton

    C.Eaton Confirmed Anschutz Nut...

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    I still think that it is lube or contamination in the hammer channel that causes power fluctuations. I still see a surprising amount of rifles with anything from moly grease to sewing machine oil on the hammer and as we know viscosity changes with temperature.
    Get all the gunk out with forensic cleaning of the hammer/channel combined with a generous buffing should see better stability. There will always be a slight variation in velocity i.e. less than 10fps which I think is to do with the hammer/valve springs but in real terms that makes zero difference down range.
     
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  3. RobF

    RobF Administrator Staff Member

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    I run my rifles dry. There’s still a change.

    Springs lose their spring as temps increase not the other way around but the effect is seen over 100s of degrees not 10. The thermal contraction/expansion again is minute. In practical terms immeasurable. You would see more change by a grain of your graphite finding its way onto the end of the spring or the valve stem base.
     
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  4. hmangphilly

    hmangphilly Floppy Quick Phil

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    Interesting

    How long did it take for the reg to react to the warmer temp in the house ?

    We can generate temp related reg pressure differences too . Ours seem to be the opposite way to what you found . ...temp increase = pressure rise .

    I enjoy showing people the gauge rise when i breathe on the reg ...( i know i need a life ).

    may have a vid some where ..........we love a vid .

    I'll have a bash today see if we can translate the pressure change to fps . That's a great idea .

    It's tricky in a steyr though ,cos the regs a bit buried . we may have to get creative . Steyr purists look away .



    Un special reg/s ......don't get excited................ just picked out of the bin ................demonstration purposes and all that ..........


     
    Last edited: Feb 6, 2019
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  5. C.Eaton

    C.Eaton Confirmed Anschutz Nut...

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    Luckily a small grain of my locksmith's graphite is very soft and if it finds it's way into the valve seat then that will probably be a good thing judging by my experiments with graphite in those nasty spring guns...;)
     
  6. hmangphilly

    hmangphilly Floppy Quick Phil

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    That's fabulous Neil .

    Tell us your secret .

    Still working on ;His Lordship' over the Mozzies . I'll bend his ear again today .He'll yield eventually .

    doyle.jpg




    mrs doyle2.png

    mrs doyle2.png

    mrs doyle2.png
     

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  7. nemesis

    nemesis 55yrd standing expert, or was it 8 or 9?

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    The steyr nickle plated barrel seemed more affected by temp. I suffered with it at the world's trying to get it set up within less than half an hour. This PH barrel;) is unafected I've found so far though it might be due to the external coating I've applied acting as a slight barrier. I can't see that some don't think that the constriction of the barrel won't affect velocity. I've seen just by holding a machined piece of metal stop the part fitting into the bore and that was from just holding it a few minutes. The heat from the hand was enough to enlarge the metal enough for it not to fit. Dont know if anyone saw it but this was also shown on Guy Martin's restoration of a spitfire where the king pin wouldn't fit after he held it.
    I've experienced a 45fps drop just by vfg cleaning a barrel too, how many micron would that remove, unless the removal of the lead acting as a lubricant was partially responsible.
     
  8. hmangphilly

    hmangphilly Floppy Quick Phil

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    My king pin swells up if i hold it firmly for any amount of time . .............theory proven .!
     
  9. C.Eaton

    C.Eaton Confirmed Anschutz Nut...

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    I've always seen a slight increase after pulling through a couple of VFG felts, never a drop.
    One thing I noticed when I had a Steyr many, many moons ago was that no matter how many felts you pulled through the barrel they never came out clean, it was like the barrel was lined with carbon.
     
  10. RobF

    RobF Administrator Staff Member

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    Some shots from the shop

    5B900BFD-7D9B-4241-B546-4C6E42BAEB24.jpeg AD178D5D-AE58-4B88-9EBE-FB9AA57C393F.jpeg B96F2F5C-A60B-44F5-9CB6-0EE6DFCE6B8E.jpeg BD3B27A5-D70F-49B5-B251-10309B9436EB.jpeg A489FD40-38B2-4B02-B436-EB01E411FAA1.jpeg 1A6F6C7B-AFA9-4C58-A057-03B720C02E04.jpeg
     
  11. nemesis

    nemesis 55yrd standing expert, or was it 8 or 9?

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    Oy oy stop wasting those feckin mozzies yer pair o tarts. :eek:
    On my vernier's they came up at bang on 6mm and the other brands at 5.33. Your at least still showing with yours a difference in length.
     
  12. DeanB

    DeanB Active Member

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    Apologies if the following is obvious but thought I would chip in...
    The internal energy of a gas = CT, the constant C is 3Nk/2 for a monotonic gas and 5Nk/2 for a diatomic gas, N is the number of molecules, k is the Boltzmann constant, and T is the temperature in Kelvin (Celsius + 273).
    So at a high temperature (Th), the internal energy is given by Eh = C Th, and at a lower temperature (Tl) the internal energy can be calculated from El = C Tl.
    Dividing one equation by the other and re-arranging gives:
    El = Eh Tl / Th - Eqn 1
    This is exactly what Jim Tyler had found and noted in a previous posting, and seems to agree with the findings of some other shooters.
    So, if you know the pellet speed at one temperature, the energy (often called power by shooters) can be calculated from:
    Energy - V V W x 15.432 / 450240 - Eqn 2
    where V is speed in fps, W is pellet weight in grams.
    The energy of the gun at the lower temperature can then be estimated from Eqn 1 and then the velocity at the lower temperature can be calculated from equation 2. This is all as suggested by Jim.
    This all suggests that it is the internal energy of the air, and hence its temperature, which has the major effect on the drop in pellet speed as the air gets colder.
    Ofcourse, you could just use a chrono when it gets cold.
     
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  13. john sears

    john sears old but not so wise

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    4C5E35A2-A56B-4D4D-BB15-942120515901.jpeg 04357A41-B5F1-40DB-9373-55A6AEF48C45.jpeg C7DB99FF-1E9E-47C6-B666-8237C37C7B11.jpeg 140E5CE2-69D3-4B0F-A767-1D197B7BE9E9.jpeg A2C30F9C-2C56-4FBC-BF27-3E28F8B9281B.jpeg E544511F-BE57-4DF0-A0E5-86A806AB3767.jpeg Here is a couple of pic from my 2009 Mozzies and 2010 Express
     
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  14. IanC

    IanC Member

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    I’m new to airguns so feel free to tell me to sod off as it may not apply to airguns but it may not just be your rifle it will be a combination of factors. I’ve hunted and shot in all temperatures while living in Canada from 40 above to 40 below and it is a given to any shooter in Canada that Air temperature changes bullet trajectory by increasing or decreasing atmospheric density, cold air makes a given load strike lower. Hot air makes the same load strike higher. Shooters can count on this. The longer the range, the more significant these temperature-induced differences in impact points.
    Cold air is more dense than hot air, so it slows bullets. Hot air expands, reducing molecular density and drag.
     
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  15. bootneckbob

    bootneckbob Active Member

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    I thought it was that simple too Ian. These boys and their mathematics; bless.

    Good job I've actually got a helmet and body armour. Body armour that floats if you please. That will be lost on anyone who hasn't had to try and swim in full combat kit!

    Sat here now waiting for the incoming!
     
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  16. RobF

    RobF Administrator Staff Member

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    The only problem with it is cold air isn't always denser than hot.

    The lowest pressure in UK was 93.8 kPa, and the highest 104.2

    So it's only the area above 'engineering toolbox' we're concerned with. You can see that it's just about possible for cold 6 degree air to be less dense than 30 degree air... funnily enough you don't often see 30 degrees in the uk, and even more rarely during a low.


    [​IMG]

    While we're here, we may as well drop the other one that humid air is less dense than dry air.

    Dive. 3ft of water stops .50 :D
     
    Last edited: Feb 11, 2019 at 11:55 PM
  17. Darron

    Darron Dwarf Slayer

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    At last another disciple of my thermal lift theory!
     
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