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Thread: The beginner's guide to air rifle power

  1. #16
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    Derek,
    Once again very lucid and informative.
    I always read the interesting snippets regarding the use of dive tanks and filling PCPs on this site.
    However the information is scattered all over this forum and difficult to absorb as it is not collated. Frequently there is an important safety issue discussed.
    With your skills would you consider doing a newbie's guide to "compressed air tanks and PCPs for dummies"?
    Many members shoot at clubs and exchange info there, but there are quite a few out in the sticks who are doing a lot of pioneering (Pioneer = the oke with all the assegaais in his back).
    Regards
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  2. #17
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    Very nice indeed, as usual.
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  3. #18
    Sharp Shooter
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    Quote Originally Posted by regbes View Post
    LOL once a nerd always a nerd

    Anyway you got me excited with those calculators so i made one in Excel

    I only have Excel 2010, but did try and make a file for older versions of excel.

    Hmm cant seem to upload the xlsx (2010 version) file, hope the save as older version one works
    Thanks regbes, it's working.
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  4. #19
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    Quote Originally Posted by regbes View Post
    When I read



    My brain automatically rejected it, as i know E=VVM/2 or kinetic energy equals half of mass times velocity times velocity

    so where the hell did this 450240 come from

    After some research and scratching formulas on a scrap of paper the explanation of the constant 450240 is as follows.

    As a starting point from my high school physics we have (FPS X FPS X Grains)/2

    First as we are measuring foot POUNDS we need to get from grains to pounds to do this we divide by 7000, i.e. 7000 grains = 1 pound

    Now we have (FPS X FPS X Grains)/2 X 7000 or (FPS X FPS X Grains) / 14000

    hmm 14000 is still around 32 times too small, so back we go to the definition of Fpe which is 1 Fpe is the amount of energy to move one pound one foot

    what is often omitted from this definition is "upwards" or against gravity.

    remembering back to high school again gravity was about 9.8 M/SS Google tells me the conversion factor from meters to feet is 0.3048
    apply this to 9.8 / 0.3084 and we get 32.16F/ss

    okay so now we have (FPS X FPS X Grains) / 14000 fighting against gravity of 32.16 to do this fighting we divide by 32.16

    leaving us with (FPS X FPS X Grains) / 14000 X 32.16 or (FPS X FPS X Grains) / 450240

    who would of thought high school science would come in handy with a hobby 20 years later

    Thanks David for a great read and workout of the grey matter
    Multiply?
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  5. #20
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    No divide, you can divide buy a number or multiply by 1 over it,
    or put another way you can divide by 2 or multiply by 1/2 or 0.5
    ((FPS X FPS X Grains) / 14000 )/32.16
    = ((FPS X FPS X Grains) / 14000 ) * (1/32.16)
    = ((FPS X FPS X Grains) *1) /(14000*32.16)
    = (FPS X FPS X Grains) / 450240
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  6. #21
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    Quote Originally Posted by jonratter View Post
    Derek,
    Once again very lucid and informative.
    I always read the interesting snippets regarding the use of dive tanks and filling PCPs on this site.
    However the information is scattered all over this forum and difficult to absorb as it is not collated. Frequently there is an important safety issue discussed.
    With your skills would you consider doing a newbie's guide to "compressed air tanks and PCPs for dummies"?
    Many members shoot at clubs and exchange info there, but there are quite a few out in the sticks who are doing a lot of pioneering (Pioneer = the oke with all the assegaais in his back).
    Regards
    Jon I've done a guide on compressed air usage:
    The beginners guide to compressed air. ~ Air Rifle SA Forums
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  7. #22
    Sharp Shooter
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    I have done a spreadsheet with power/pellet and velocity combinations:
    Top row indicates fpe, must still do custom BC values for all pellets.

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  8. #23
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    Thank you so much it really helped me!!!!!!!!!!
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  9. #24
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    Thanks this is the info all new comers need to read and know.Why don't you have it permanently posted on the forum I feel info like this need to be available for all especially new comers like me
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  10. #25
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    Good one Derek. I always advise people to start with a rifle around the 8Fpe range.
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