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Which is more important in ballistics?

Discussion in 'Handguns: General Discussion' started by IMTHDUKE, Sep 22, 2012.

  1. Kleanbore

    Kleanbore Moderator

    Posted by 481, in response to "but that [that momentum is conserved in an inelastic collision] does not mean that momentum is the determinant of the distance that an object will travel after being captured in an inelastic collision":
    Do you really and seriously believe that the distance required to stop a moving object by applying a constant force is proportional to the velocity, rather than to the square of the velocity? That is, to momentum, rather than to energy?

    Have you ever conducted any experiments in that area?

    Consider this.

    Or if you prefer, see this.

    That is, distance varies proportionaly with energy.

    Yes, force is equal to mass times acceleration. Do not forget that distance is equal to one half the acceleration times the square of the time. We're dealing with force times distance which is work which is energy-- not momentum.

    That momentum is conserved is irrelevant--it doesn't the determine distance traveled by the moving object. Energy does. Momentum transfer does determine the resultant velocity of the combined mass of the target and the bullet--which, in the case of a 100kg target and a pistol bullet, is insignificant.

    That someone has been able to greatly simplify modeling by correlating distance and other things with momentum is a wonderful thing--but it does not mean that work is equal to momentum, or that force times distance is momentum.
  2. 481

    481 New Member

    Yep, if the force, defined as F = m ∆v/∆t required to decelerate an object is proportional to 1/2MV^2, then it is also proportional to MV (momentum)- the first derivative of 1/2MV^2.

    Are they no longer teaching the calculus with physics? :confused:

    Just as these descriptions are descriptions of energy expenditures over a given distance and period of time, so too are they descriptions of F = m ∆v/∆t- the force you describe acts also to reduce the mass' velocity over that same ∆t changing the object's velocity and therefore, its momentum. It is called impulse.

    Yep, and distance may also be expressed as s = vt.

    Actually, the object posseses both quantities, but in the deceleration of any mass, the most direct way to analyse that motion is through the linear relatonship of s = v∆t with respect to ∆x (distance). It is as valid as any energy based analysis, but far simpler and more convenient to conduct.

    Oh, it most certainly does. Did you really just say that? :what:

    If an object has momentum, it is in motion. When a force acts to reduce or increase momentum, it does so over a period of time causing a change in velocity, ∆v/∆t, and also results in a displacement of the object.

    I've never heard Newton's third law of motion, MV = MV, referred to as being "irrelevant".

    You see those "V"s up there in the expression "MV = MV" ? That's motion (velocity) which over a period of time equates to distance unless these events occur instantaneously, that is with t = 0. Not possible. So yes, momentum is directly proportional to the distance than an object will move.

    Nope, work is proportional to momentum just as it is proportional to energy, but I digress- I covered that derivative relationship in the first sentence of this response.
    Last edited: Sep 26, 2012
  3. Kleanbore

    Kleanbore Moderator

    To be proportional, the relationship must be linear.

    What is it that you are trying to say?
  4. Eb1

    Eb1 New Member


    The size of the hole from an unexpanded bullet.
  5. 481

    481 New Member

    If that is the case, then how can you say this? :confused:

    Energy vs. distance traveled (∆V w/respect to ∆x/∆t) is not a linear function-

    Are you messin' with me, KB? C'mon. I mean, you do know what a derivative is, don't you? :confused:

    Inhomogeneous first-order linear constant coefficient ordinary differential equation: cv + x^2 = dv/dx
    Last edited: Sep 26, 2012
  6. Kleanbore

    Kleanbore Moderator

    Energy equals force times distance.
  7. 481

    481 New Member

    Um, yeah...that's great, but it doesn't address the question asked.
  8. Certaindeaf

    Certaindeaf member

    In a world of compromises, all men do.
  9. 2zulu1

    2zulu1 Active Member

    FWIW, consider this;

    Let's remember we are discussing fluid flow dynamics, not brake temperatures.

    An expanding bullet with 1800 ft/lbs of energy raises the temperature of three pounds of water by 1F.

    FWIW, I have both of these references, but I prefer the "Quantitative Ammunition Selection" book to MacPherson's WTI book. it's an easier read and the author does a great job of walking the reader through the mathematical equations needed if they wish to test their carry ammunition, factory or handloaded. Since I live in a very rural area, both of these books have assisted me greatly in determining bullet selection/caliber based upon potential four legged threats. Not any gel data for 38Super loaded with 357mag bullets. :)
  10. Certaindeaf

    Certaindeaf member

    So what focus does this work subscribe to? Are all projectile types held constant or is it just fuzzy numbers/math? If all projectiles are not the same type, it's still just begging the question/s.
    Since you live in a very rural area, maybe just shoot prospects into some creek mud and go with that?
  11. Kleanbore

    Kleanbore Moderator

    The question asked was, "In a defensive rd for a handgun which is more important to consider....muzzle velocity or muzzle energy?"

    At first glance, that seems nonsensical. Energy is a function of velocity and mass. But the discussion has flushed out more. Perhaps this will summarize things well enough:

    • In handgun bullets, energy is not an imprtant factor in determining wounding effectiveness.
    • The important factors are the following:

    1. Where the bullets hit, and in what direction, in a 3D human target
    2. Penetration
    3. Bullet diameter

    The first one does not refer to bullseye accuracy; the target is likely to me moving fast, and the defender will not have time to aim accurately, or to reliably make one shot hit where he or she would like, and rapid repeat fire is likely to be needed.

    Penetration into a given medium is a function of velocity, mass, diameter, bullet shape, and bullet construction. It can be measured by firing into surrogate materials that are generally representative of human targets. Predicting the results of that kind of tests using the results of penetration in water has been done.

    There is not a lot of difference between the diameter of an expanded .45 bullet and that of an expanded 9MM bullet. A .45 will generally have a lower magazine capacity and, in a firearm of similar size and weight, greater recoil, which will make rapid repeat shots more difficult.

    It hasn't been discussed much in this thread, but some may not realize that boom, blast, and fuss at the muzzle does not translate into "knockdown power." There's really no such thing.

    There is insufficient information available, and there are far too many variables involved, for anyone to draw any meaningful conclusions from the results of real-world shooting incidents.

    Personally, I do not see the point in spending much time trying to decide whether the modeled or tested performance of one particular round is marginally better than that of another. Given reasonable published assurances that all of my choices meet minimum standards (I'm happy with FBI standards), I will base my choices on reliability in my handgun, availability, and price, in that order.
  12. 481

    481 New Member

    CD, You can read for yourself here-


    copied/pasted from various parts of the website-

    QUANTITATIVE AMMUNITION SELECTION presents a mathematical model that allows armed professionals and lawfully-armed citizens to evaluate the terminal ballistic performance of self-defense ammunition using water as a valid ballistic test medium. Based upon a modified fluid dynamics equation that correlates highly (r = +0.94) to more than 700 points of manufacturer- and laboratory-test data, the quantitative model allows the use of water to generate terminal ballistic test results equivalent to those obtained in calibrated ten percent ordnance gelatin. The quantitative model accurately predicts the permanent wound cavity volume and mass, terminal penetration depth, and exit velocity of handgun projectiles as these phenomena would occur in calibrated ten percent ordnance gelatin and soft tissue. With a confidence level of 95%, the model predicts the terminal penetration depth of projectiles in calibrated ordnance gelatin within a margin of error of one centimeter.

    The book sure was a learning experience for me. :)
    Last edited: Sep 27, 2012
  13. 481

    481 New Member

    Great post.

    Well, Kb, I'll say this- you and I agree about as completely as two folks can about the vast majority this stuff. I doubt that there is any significant difference between our points of view- even if you were messin' with me for a bit! :D
  14. brickeyee

    brickeyee New Member

    Then you have a very limited understanding of physics.

    Billiard balls are nearly 100% elastic collisions.
    VERY little energy is lost.

    A punching bag is at the opposite end, an almost 100% elastic collision.
    The bag deforms absorbing the energy.

    Human tissue is not exactly a liquid very amenable to simple fluid dynamics analysis in many cases.
    It is NOT isotropic (uniform) in composition, strength, density, or much of anything else.
    The fact that cells have a high concentration of water does not remove the other components that give them shape and form.

    There is a reason we do not look like jellyfish.
  15. Kleanbore

    Kleanbore Moderator


    Good answer.

    McPherson points out the complexity associated with the conversion of kinetic energy to thermal energy in what he calls "real" collisions. The real collisions were not fluid dynamics events.

    But: and it hadn't occurred to me, by firing into water, he was able to greatly simplify things by using a virtually pure momentum transfer experiment in which energy transfer was insignificant. Correlation with (gelatin representatives of) real collisions was the next trick.

    By the way, I never realized that it was an interview with McPherson I was watching when he set the record straight for those who had concluded from the movement of a target's head (through which the bullet had passed) that they could prove the direction from which the shot had come.
  16. 481

    481 New Member

    Ya see, when you say stuff like this, it makes me think that you'd enjoy reading books like MacPherson's Bullet Penetration and Schwartz's Quantitative Ammunition Selection.
  17. Skribs

    Skribs New Member

    Bullet design will affect greatly how much energy you need. Essentially, you want to make a hole 12-18" deep and have it go as wide as possible. Handgun rounds aren't going to have enough energy to create the kind of permanent cavitation you'll see from rifle rounds.
  18. 2zulu1

    2zulu1 Active Member

    You're correct, I have a very limited knowledge of physics; but, I can accurately calculate bullet penetration in soft tissue based upon data obtained from a bullet captured in water.

    Perhaps you can share with us your bullet penetration calculations based upon punching a billiard ball.
  19. MCgunner

    MCgunner Active Member

    Velocity really doesn't matter, only in the energy equation. It is energy that matters and at 500 fps + or -, the ballistic pressure wave matters. No, it's not a "reliable mechanism" if the shot isn't accurate in the proximity of a major nerve network, but I've seen the results and seen actuall remote tissue damage from a bullet's pressure wave NOT involving nerve tissue, even from a 165 grain Keith style SWC fired at 1800 fps making around 1200 ft lbs ME. Animal was 80 yards down range, so energy was in the 700 ft lb range with velocity down to around 1400 fps near abouts. Ths was a lung shot behind the shoulder on a 110 lb whitetail doe that jumped upon being shot and went about 20 yards before piling up. Around 2-3 seconds max, maybe less, not more, from hit to death with a lung hit, no other vitals, just the lung.

    That's just one instance. I've seen lots more from calibers like 9x19 +P on trapped hogs, enough to make me a believer in the 9mm as a self defense caliber. I like the confidence in having used the gun on something over and over and seeing the results.

    But, you can't shoot something in the foot and expect it to be immediately lethal. You still must put the shot in the right place. Whatever mechanism works is the one I'll run with. If none are immediately effective, try again. You cannot count on one shot from a .338 win mag to stop a person. You have to put the shot in the right spot and then you'd better be ready for a back up.

    I'm not sure what all this arguing over Fackler vs Courtney accomplishes in the real world. I carry what I carry because it's small enough to easily conceal and I have confidence in my ability to make a shot with it and confidence in the round to do the job. Don't need math to figure that out. :rolleyes:
  20. ArchAngelCD

    ArchAngelCD Active Member

    Neither, IMO ACCURACY is most important because the best bullet in the world traveling fast and hitting hard will do little to no good unless you make good hits. If it comes down to a few fps choose the ammo that's most accurate in your handgun.

    Decades ago when bullet construction was poor a wide heavy bullet moving fast was necessary. With today's bullet technology a JHP bullet can be traveling as slow as 800 fps and reliable expand. ACCURACY is the key...

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