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Question one for the smart people...

Discussion in 'Anything Airgun Related' started by jamessuper10, Oct 29, 2008.

  1. jamessuper10

    jamessuper10 Engaging Member

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    was driving to work yesterday evening and was thinking... 1. would a pellet have more or less velocity, depending on the level above or below sea level? 2. would the atmospheric pressure alter the path of the pellet.

    curious questions i know, i used to play a lot of golf back in South Africa, and i found that i could hit a golf ball a lot further at sea level than i could above sea level, now im sure that there are a load of variables that are involved in this but the science of it is the same, thus it must work...
     
  2. Bark

    Bark Newbie

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    High flyers

    I live at a little over 4OOO' and have noticed a marked difference when shooting my lanes near the house compared to shooting at my club which is very close to sea level.POI and crony numbers are both higher at altitude,I believe BC goes up about a point or so for each 1000'.
     
  3. Buzz

    Buzz Banned

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    Depends on what type of gun you're shooting and what conditions prevail on the days you shoot.
    If we say we could shoot at sea level at 9 in the morning, on a day when the temperature at sea level is 20C and the barometer shows 1013 millibars and then at 9.01 we could shoot at 4,000ft altitude, the major differences would be these.

    The temperature would have fallen by about 8 degrees (2 degrees/1000ft) to 12C, the pressure would have dropped by about 133 millibars (about 1mb/30ft) to 880.

    So if you were shooting at 4000ft with a PCP like an AA S410, the amount of energy within the gun wouldn't change, because you charge it to a given pressure. The air outside the gun would be thinner (just a bit), so the muzzle velocity should be a tiny bit higher, but the velocity down range would be slightly higher than at sea level, because of the lower drag of the thinner air. This effect of less drag wouldn't be as much as you'd expect, because as the pellet would be travelling faster, the drag would increase a bit (by the square of the speed).

    Same conditions but with a springer would be a totally different case. The air that powers a spinger is obviously the same as the surrounding air, because it's sucked in to the cylinder when you cock it. So at altitude there is actually less air in the cylinder than at sea level, so when you pull the trigger it compresses less and produces less power to the pellet. The result of that is a pellet that has less muzzle velocity. Being as it's travelling slower it has less drag, add to that the fact that the air is thinner producing less drag, the down range speed won't drop as much as it would at sea level, but the overall pellet speed would be down on the sea level figure.

    CO2 guns in the same conditions would be similar to the springer, but because the CO2 cartridge can't be filled at altitude. It has the pressure in it at the time you bought it and has less pressure at 12C than it does at 20C...not by much with just a small difference like 8C, but it's there.

    A multipump pump gun is in essence a PCP, the only difference is that you have to pump it after each shot, so it would act very similar to the PCP at altitude.

    So the higher you go the more a PCP will win over the other two.

    The point I didn't make, was that if you shoot one day in a certain set of conditions and then shoot again at the same place in a vastly different set of conditions, the changes detailed above will still happen, so it's not really just an "altitude" thing, but more of an "atmospheric conditions" thing.
     
    Last edited: Oct 29, 2008
  4. 8-ball

    8-ball Engaging Member

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    All sounds far too technical for me...I like things kept plain and simple - a bit like me!
     
  5. Buzz

    Buzz Banned

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    Sorry Ken, James did ask :D
     
  6. 8-ball

    8-ball Engaging Member

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    The question had me confused then tried reading the answer and got even more muddled - I'll try again later and see if I can get my head around it as it sounds very interesting.
     
  7. Buzz

    Buzz Banned

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    Looks like a nice RV :D
     
  8. hughie

    hughie Posting Addict

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    Never knew airgunning could be so complicated.:D All i understood about that was that springers are worse than PCP's at alttitude. :eek:
     
  9. johnbaz

    johnbaz Big Poster

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    i think it's to do with gravity (no not gravy- that would slow the pellet down immensly, well our lasses gravy would anyhow:p:p)

    the farther away from the the earths core you are, a lesser pull is exerted and so a projectile would travel further before it lands, also the air is thinner at altitude so air resistance would impede the pellets progress to a lesser extent....

    flippin'ell- did i just type that:eek::eek::eek::eek::eek:


    john:D:D
     
  10. 8-ball

    8-ball Engaging Member

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    ..now that makes sense...thankyou :up:
     
  11. Buzz

    Buzz Banned

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    except for the fact that the Earths gravity is keeping the moon in orbit and that's 250,000 miles away, how much difference do you think a few thousand feet's going to make.
     
  12. johnbaz

    johnbaz Big Poster

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    but then again there are sattelites' up there that don't fall on us (well not very often anyhow),they are nowhere near a quarter of a million miles away, it may be to do with the mass of the item that's being pulled to earth....

    everything has it's own gravity too, but the larger the item, the more gravity it exerts, on some of the larger planets the pull is so strong that you wouldn't be able to hold your own weight up but then again on our moon which is much smaller than the earth, there is only 1/6
    th of the pull of our gravity...

    john:eek:
     
  13. Buzz

    Buzz Banned

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    I understand that this may be going over the heads of a lot of people, but gravity is a tremendous subject. If you tie a brick to a piece of string and whirl it around, the brick goes round in a circle.....it's orbiting you. You feel a pull on the string which is actually called centripetal force and it's that pull that keeps it whirling around you instead of flying off at a tangent. If you tie too big a brick to the string, or whirl it round too fast the string would break and off it would go. It's exactly the same with things orbiting the earth, except the string is replaced by gravity. Centipetal forces vary depending on several things. Mass of the object, it's speed and the radius of the curve its making and that's why differing sizes and mass orbit the Earth at differing speeds and distances.

    It has nothing what so ever to do with why projectiles act differently at the top of a mountain to the bottom, but has everyting to do with why slow projectiles have a more curved trajectory than those travelling faster. In fact, if you could have a rifle that would fire a projectile at speeds in excess of 17,000 mph. the projectile would climb into earth orbit or even beyond, depending on it's speed.

    If anyone would like me to go deeper into this feel free to open up another thread or do a google search for earth orbit parameters and be prepared for some pretty heavy going, but this thread should go back on topic I think.
     
  14. hughie

    hughie Posting Addict

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    Perhaps we ought to have a physics section on the forum.
     
  15. Buzz

    Buzz Banned

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    By the looks, it wouldn't have many members:D
     
  16. johnbaz

    johnbaz Big Poster

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    thanks buzz- i stand corrected:eek:

    i ought to have said that i was summizing my answer rather than actually knowing it:eek::eek::eek:


    john:)
     
  17. hughie

    hughie Posting Addict

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    Too right . I dont think physics is the top priority for most airgunners . Me included:D
    I 've read that bit a bove about three times and still cant get my head round it. Is there a more simple way of putting it with a maximum of about 5 lines :Dso that people like me can understand. :eek:
     
  18. Buzz

    Buzz Banned

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    No..............:D The answer to the original question is post number 3...the higher you go the thinner the air is. This helps in some ways and hinders in others...that's about as simple as it can get.
     
  19. jamessuper10

    jamessuper10 Engaging Member

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    wow... im gob smacked buzz! eather you have to much time on your hands or you really know your stuff! im thinking you know ur stuff....:) thanks for the info
     
  20. i8allthepies

    i8allthepies Posting Addict

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    Correct, James, he does know his stuff:up:
     

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