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Thread: Formula for converting ft lbs to lbs per square inch

  1. #1

    Formula for converting ft lbs to lbs per square inch

    Is there a formula for converting ft lbs to lbs per square inch?
    I.E for the sake of the question, if a given bullet produces say 1000 ft lbs of muzzle energy, what would the figure be in lbs per square inch?
    Would it be 1/144th of the ft lbs figure?

  2. #2
    ft/lbs is not a pressure measurement. Its an Energy measurement and cant be converted into a pressure measurement.

    what is it you are trying to do?

  3. #3
    As stated the two measurements are for different things, there is no (readily available) direct correlation between ME and chamber pressure. I assume this is what you are looking for.

  4. #4
    that formula is for converting between units of energy i.e. 'lbs of force per square foot' to 'pounds of force per square inch' then yes e.g. on a torque driver; but not converting energy to pressure as the others have already stated.

  5. #5
    Quote Originally Posted by TikkaT3 View Post
    Is there a formula for converting ft lbs to lbs per square inch?
    I.E for the sake of the question, if a given bullet produces say 1000 ft lbs of muzzle energy, what would the figure be in lbs per square inch?
    Would it be 1/144th of the ft lbs figure?
    So if a .250" diameter bullet is carrying 100ftlb energy, you want to know what pressure in lb sq in it hits the target at ?
    Is it not as simple as working out the surface area of the bullet nose, dividing it into a square inch and X by the 1000ft lbs ?
    And no applied mathematics is not my strong point

    Neil.

  6. #6
    Quote Originally Posted by Hornet 6 View Post
    So if a .250" diameter bullet is carrying 100ftlb energy, you want to know what pressure in lb sq in it hits the target at ?
    Is it not as simple as working out the surface area of the bullet nose, dividing it into a square inch and X by the 1000ft lbs ?
    And no applied mathematics is not my strong point

    Neil.
    Exactly Hornet, "what pressure in lb per square inch it hits the target at" If it is known for the purposes of this question that a bullet produces 1000ft lbs (1000lbs of energy per 1 square foot ?), there must be a way of calculating the equvilent figure per square inch? stands to reason doesn't it?
    This is why i thought that as there are 144 square inches in a square foot, the figure would be 1/144th of 1000, I.E for the 1000ft lbs quoted, 6.944 lbs per square inch?
    or have i got it wrong

  7. #7
    For your calculation, 1000 lbs per square foot of muzzle energy is 6.944 lbs per square inch of muzzle energy.

    BUT, this NOT the "pressure in lb per square inch it hits the target at" because muzzle energy (i.e. the bullet's kinetic energy at the muzzle) is not pressure; so you cannot calculate it using your formula.

    To calculate the energy at the target, you would need to factor in velocity and bullet weight.
    Last edited by JabaliHunter; 14-03-2012 at 16:41.

  8. #8
    Is'nt a straight forward kinetic to potential energy conversion? Good old Newtons laws. You would need to know other factors within the calculation other than just the ft/lbs though.
    Below is a link to my website.
    Quad sticks

  9. #9
    you can calculate the PSI created on impact but you can't CONVERT to get it.

    you need more info.

  10. #10
    so, what info would we need and does anybody on here know how to to do it?

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