Page 1 of 2 12 LastLast
Results 1 to 15 of 21

Thread: working out FT LBS TO FPS

  1. #1
    Join Date
    Nov 2007
    Location
    doncaster
    Posts
    83

    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
    Join Date
    May 2008
    Location
    lutton nr spalding
    Posts
    562
    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
    Join Date
    May 2008
    Location
    lutton nr spalding
    Posts
    562
    thought they had 3 power ratings that you could switch between,
    aa s409k .177, cs700 stock, mtc mamba 4-16x50, logun qgs

  4. #4
    Join Date
    Jan 2008
    Location
    Mold (Yr Wyddgrug) N.Wales
    Posts
    14,131

    true mate

    but to err is human my friend
    Rapid 7 S .22 10-22 S + B 6 x 42 Stiller Predator full custom.204 NSX 5.5-22x56 Tikka T3 semi custom .204 Remy PSS .223 NSX 12-42 Remy Var.243 Zeiss Conquest - Beretta 692 adjustable 30" Winchester Red-Performance SX3 12g

  5. #5
    Join Date
    Mar 2008
    Location
    Rochdale
    Posts
    337
    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
    Join Date
    Apr 2007
    Location
    Haverhill, Suffolk
    Posts
    538
    Theoben MFR CS800 .177/Burris Timberline, Theoben Evo .177/ Burris Timberline, BSA Supersport .25, Haenel XX, BSA Ultra .177/ Burris Timberline.

  7. #7
    Join Date
    Jun 2008
    Location
    Horsham
    Posts
    26
    >>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
    Join Date
    Jan 2008
    Location
    grantham
    Posts
    222

  9. #9
    Join Date
    Nov 2007
    Location
    doncaster
    Posts
    83
    some good sites here people

    thanks alot

  10. #10
    Join Date
    Mar 2001
    Location
    Long Eaton, England
    Posts
    3,589

    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
    Join Date
    Sep 2004
    Location
    Colchester, Essex - Romano-Saxons with Guns.
    Posts
    4,246
    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
    2006 Browning Phoenix Hunter: 1993 Beretta A303 Supersport: Air Arms 1998 Mk.2 Pro-Target, 2001 Mk.2 Pro-Sport & 2003 S400C

  12. #12
    Join Date
    Nov 2007
    Location
    doncaster
    Posts
    83
    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
    Join Date
    Aug 2002
    Location
    Guildford, Surrey
    Posts
    1,790

    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
    Join Date
    Sep 2004
    Location
    Colchester, Essex - Romano-Saxons with Guns.
    Posts
    4,246
    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
    2006 Browning Phoenix Hunter: 1993 Beretta A303 Supersport: Air Arms 1998 Mk.2 Pro-Target, 2001 Mk.2 Pro-Sport & 2003 S400C

  15. #15
    Join Date
    Mar 2008
    Location
    Rochdale
    Posts
    337
    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.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •