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Thread: working out FT LBS TO FPS

  1. #1
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    working out FT LBS TO FPS

    hi there

    im looking for information
    how to convert
    780fps to ft lbs
    or a 1000fps

    ive found nothing to help
    so im wondering if anyone here can

    thanks

  2. #2
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    http://extorian.co.uk/shooting/pellets.html

    depends on pellet weight

    8.4 grain@ 780 fps= 11.35lbft
    8.4 grain @ 1000 fps=18.66lbft
    aa s409k .177, cs700 stock, mtc mamba 4-16x50, logun qgs

  3. #3
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    thought they had 3 power ratings that you could switch between,
    aa s409k .177, cs700 stock, mtc mamba 4-16x50, logun qgs

  4. #4
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    true mate

    but to err is human my friend
    Rapid 7 / 10-22 ATN 2 Stiller Predator .204 Pulsar N970 Tikka T3 semi custom ATN MARS thermal.204 Tikka T3 Semi.223 Wylde IOR Operator Lawton 6mmBR Kahles Gen 3 - Stiller 6.5 x 47 Bushnell BDX - Winchester Red Performance SX3 12g

  5. #5
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    Quote Originally Posted by a88ott View Post
    hi there

    im looking for information
    how to convert
    780fps to ft lbs
    or a 1000fps

    ive found nothing to help
    so im wondering if anyone here can

    thanks
    You need to know the weight of the pellet in grains (some tins do have the weight written on them).

    Say you are using a pellet that weighs 7.5gns.

    The formula is:

    Muzzle velocity squared, multiplied by the weight of the pellet, divided by 450240.

    The result is in ft/lbs.

    780x780=608400
    608400x7.5=4563000
    4563000/450240= 10.13ft/lbs.


    This is a formula that I have used since the 70's so there may be an easier or better method of working it out and if this is the case I'm sure that someone will come along and correct me.
    I hope this is of assistance.

    Regards,
    Gary.

  6. #6
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    Theoben MFR CS800 .177/Burris Timberline, Theoben Evo .177/ Burris Timberline, BSA Supersport .25, Haenel XX, BSA Ultra .177/ Burris Timberline.

  7. #7
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    >>Muzzle velocity squared, multiplied by the weight of the pellet, divided by 450240

    Spot on. Looks a bit weird but it's because of the units used - grains, pounds, and feet.

    The kinetic energy of a pellet leaving the barrel is:

    (pellet weight x (speed x speed)) / 2

    This is nice and easy using SI units:

    (Kg x (m/s x m/s)) / 2

    i.e. (pellet weight in grams / 1000 x (speed in metres/second x speed in metres/second)) / 2

    The result is the energy in joules.

    It gets a bit messy in imperial because grains isn't a simple fraction of a pound. But the figure of 450240 is a simple way to convert grains to pounds and also apply the division by 2 in the formula. So, you put in feet/second and grains and out pops the energy in lb/ft.

  8. #8
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  9. #9
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    some good sites here people

    thanks alot

  10. #10
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    Spot on...

    Quote Originally Posted by gtfreight View Post
    You need to know the weight of the pellet in grains (some tins do have the weight written on them).

    Say you are using a pellet that weighs 7.5gns.

    The formula is:

    Muzzle velocity squared, multiplied by the weight of the pellet, divided by 450240.

    The result is in ft/lbs.

    780x780=608400
    608400x7.5=4563000
    4563000/450240= 10.13ft/lbs.


    This is a formula that I have used since the 70's so there may be an easier or better method of working it out and if this is the case I'm sure that someone will come along and correct me.
    I hope this is of assistance.

    Regards,
    Gary.
    Stick with this formula!

    Tony
    If you wade in, you have to risk the water coming over the tops of your wellies...

  11. #11
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    I think what the man is after is, the theoretical maximum muzzle velocity of a 12 ft/lbs air rifle, depending upon the weight of the pellet being used. At the end of This Link, is an image of the usual formula re-arranged to make Muzzle Velocity (in feet per second) the subject. You'll need a calculator with a square root key - use Windows' own calculator. Regards ... Geek
    PauL H. - Shotgoon
    Brownings: 1999 Ultra XS; 2004 B525 Field; 2010 Maxus Hunter: Air Arms 1998 Mk.2 Pro-Target, 2001 Mk.2 Pro-Sport & 2003 S400C

  12. #12
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    ok thanks

    but how do i find the Muzzle velocity
    on a air rifle ?

    thanks

  13. #13
    alan-aitch. is offline Burris Burris Burris Burris Burris Burris
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    Try this......

    Click

    You can edit the pellet list to add your pellet and weight, (look in the help file) then you can input the required ftlb and it will tell you the fps for the selected pellet, or you can input the fps and it'll tell you the power.

    Alan.

  14. #14
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    Quote Originally Posted by a88ott View Post
    ok thanks

    but how do i find the Muzzle velocity
    on a air rifle ?

    thanks
    Use a Chronoscope, though some people call these devices Chronographs. Regards ... Geek
    PauL H. - Shotgoon
    Brownings: 1999 Ultra XS; 2004 B525 Field; 2010 Maxus Hunter: Air Arms 1998 Mk.2 Pro-Target, 2001 Mk.2 Pro-Sport & 2003 S400C

  15. #15
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    Quote Originally Posted by a88ott View Post
    ok thanks

    but how do i find the Muzzle velocity
    on a air rifle ?

    thanks
    If you don't know the muzzle velocity you can't work out the kinetic energy in ft/lbs.
    I don't understand why you give a fps reading for conversion, then you ask how to find out how to get fps.
    You can buy inexpensive chrono's (Combro) for about £40 that attach to the end of your muzzle and they will give you a read out in fps. They can also convert this into ft/lbs if you know the weight of your pellet.
    Regards,
    Gary.

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