SD Ammo, SD, and what it means and why - Page 2

SD Ammo, SD, and what it means and why

This is a discussion on SD Ammo, SD, and what it means and why within the Defensive Ammunition & Ballistics forums, part of the Defensive Carry Discussions category; For my two cent's worth (which is only worth a penny anymore), I must also agree with glockman10mm in favoring (a) larger caliber first and ...

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Thread: SD Ammo, SD, and what it means and why

  1. #16
    Member Array Eaglebeak's Avatar
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    For my two cent's worth (which is only worth a penny anymore), I must also agree with glockman10mm in favoring (a) larger caliber first and (b) a heavier bullet in any caliber as generally being my favorite for stopping people at very close range - and not elephants, rinos, or a pesky bear in a tree stand at a considerable distance.

    There are so many different and confusing physics aspects to consider about any particular bullet and the speed at which it's travelling that pertain to the related penetration into a chunk of meat and the force being applied to said chunk of meat while penetration progresses. Depending on the game you're intending to drop and the distance involved, all of those physics factors combine very differently when trying to determine which particular combination of those factors will be most effective for the intended purpose. SD (sectional density) is a very important penetration aspect of bullets having the same cross-sectional diameter (caliber); but there is also the major increase in applied energy being absorbed by the piece of meat (as penetration progresses) that is directly proportional to an increase in the bullet's cross-sectional diameter (CSD) as well. Another frequently overlooked major ingredient to the stew is mass-inertia (MI) of the projectile at any given velocity.

    SD has already been very comprehensively covered, so I'll try to quickly brush upon CSD (cross-sectional diameter) and MI (mass inertia) as two other important factors to consider. Granted, the muzzle-energy (or just plain ole energy) can be matched by a lighter projectile running at higher velocity with that of a heavier projectile running at a lower velocity; but simply looking at say 900 ft/lbs of equal energy delivered by two different bullets of different weights and/or diameters is not "equal" in effect by any means whatsoever. "Penetration" makes a hole that severs blood vessels and/or internal organs that will eventually cause the demise of a living target just like an arrow, knife, or ice pick easily do; but without concurrently delivering (and expending) a great amount of energy (force) upon the target, it will either run away to die, chew you to pieces, or empty a magazine in your direction before eventually collapsing. If I should stab and deeply penetrate an attacker with eventually fatal wounds with a knife, arrow, or ice pick, that attacker would still pose a major threat to my life for a considerable length of time. If I should soundly whack an attacker with a baseball bat, he/she would instantly get knocked flat on his/her a$$ and be totally incapacitated (threat stopped) for a considerable length of time even though there was no penetration or an eventually fatal wound inflicted. Why? Because I have delivered (and they have absorbed) an immense amount of shock-force (energy directly expended upon the body) that instantly removed the threat they posed whether a fatal wound was concurrently delivered or not. Remember, self-defense is "stopping the threat" and not necessarily "intending to kill" - stuff that can easily crucify you later in criminal or civil court.

    When considereing CSD alone with regard to "equal" muzzle-energy, one could easily drive a .22 bullet fast enough to contain the same energy as a much slower-moving .45ACP bullet (let's say again around 900 ft/lbs). However, the very narrow CSD of even a hollow-point .22 bullet at such high velocity would cause it to completely penetrate and fully exit soft tissue of a human body with the bullet retaining a great amount of its initial energy upon exit; therefore, while a fatal wound may have been created, the body most likely only felt a "sting" because it only absorbed less than 100 ft/lbs of bullet's energy before it exited. However, the .45ACP bullet with a much wider CSD would logarithmically see a much higher resistance to penetration depth while it's slower velocity would also combine to stop the bullet inside the target without exiting; therefore, whatever wound was created is greatly augmented by the "baseball bat" effect of the body absorbing the full 900 ft/lbs of bullet energy.

    Even when bullet weight, CSD and SD are relatively equal, the velocity at which the bullet is travelling will also create a major difference in the effectiveness of shock-force (energy absorbed by the target). Anyone who has been in combat, worked an ER, or taken a bullet themselves will quickly attest that a high level of force absorbed by the body (and inernal organs) can be fatal when the wound itself wouldn't have been. Case in point was the "Son of Sam" serial killer from many years ago who walked up to his victims and fired point-blank with a .44 magnum short-barreled revolver using hollow-point bullets. While he killed many people before he was caught, less than half of his victims died as a result of their wound(s) because every shot from the high-velocity .44 mag at such close range (irregardless of the hollow-points) completely penetrated the victims with very little bullet expansion which (in turn) expended very little of the bullet's energy on their body as it quickly passed through. Therefore, the survivors were ones that didn't suffer a fatal penetration wound when there was a minimal shock-force concurrently applied to the body as well. While the facts weren't widely publicized, every law enforcement agency, combat veteran, and medical trauma expert were in total agreement that the death rate (considering the wounds inflicted) would have most likely been over 90% had he been using a much lower-velocity .45ACP that would have added a much higher blunt-force trauma to the physical wound itself.

    The MI (mass inertia) factor is easy to visualize by considering if you would rather try using your arm to deflect a soccer ball or a bowling ball that were both coming toward you at the same velocity. Maybe also think about taking a running start to either punt a soccer ball or a bowling ball with all your might. The simple physics definition is that "inertia of motion" means that matter in motion tends to remain in motion, and will offer a restance to its motion being slowed or deflected in another direction with a counter-force that is directly proportional to its mass density (weight/inertia = MI) - which quickly becomes apparent when trying to stop the soccer ball or the bowling ball with your arm (or head). In the same respect, the "inertia of rest" means that matter at rest tends to remain at rest, and will oppose any force trying to put it in motion with a counter-force directly proportional to its mass density (weight/inertia = MI) - which also becomes apparent from the force applied to your toe when punting a soccer ball or a bowling ball.

    The MI stuff sounds like mumbo-jumbo to many, but the "inertia of rest" is why your heater has a significantly higher recoil (using the same powder charge) with a heavy bullet than it does with a lighter bullet. In the same respect, the "inertia of motion" is why a light weight bullet (especially at high velocity) is easily deflected off target by nothing more than hitting a fly or tiny twig in its path - while a heavy bullet of lower velocity will bulldoze its way through thick brush to find its intended mark. In bad memory days of stinking Nam jungles, an M-16 on full auto was virtually worthless when shooting through even light cover; and there is personal witness of many instances when (what should have been a fatal shot) was deflected away from internal organs when it hit a rib and took more rounds to finish the job - unfortunatly, not before the target inflicted a casualty of our own on more occasions than I care to remember. In a "heavy cover" close-range firefight, the smart ones were pulling their .45ACP and praying to God that the point and/or drag men were still alive and effectively mowing the lawn with their bootleg Brownings spraying 00-buck into the bush that quickly sent the survivors into disappearance mode.

    MI and lower velocity in close-quarter situations definitely have major advantages when conditions are far from being textbook perfect according to all the whoopie high-tech ballastics and modern tactical crap. Consider the fact that far more soldiers have fallen from a primitive, 450-grain, .58 caliber, black powder musket round at close range than from anything that ever came along later. Just food for thought.


  2. #17
    VIP Member Array glockman10mm's Avatar
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    Eaglebeak thank you for adding the CSD portion of the equation. It was getting late, I'm not a good typer, and my brain was getting a little numb. You conveyed brilliantly the portion I missed.

    The only way to compensate for CSD, is SD. And the smaller you go, the more you have to compromise. But since SD always favors the smaller caliber in it's heaviest loadings, all is not lost.
    Thanks for your contribution, and service to this country.
    Ignorance is a long way from stupid, but left unchecked, can get there real fast.

  3. #18
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    "Case in point was the "Son of Sam" serial killer from many years ago who walked up to his victims and fired point-blank with a .44 magnum short-barreled revolver using hollow-point bullets."


    It was well publicized that David Berkowitz used a Charter Arms Bulldog .44 Special.

    Suspect in 'Son of Sam' Murders Arrested in Yonkers; Police Say .44 Caliber Weapon Is Recovered
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  4. #19
    VIP Member Array smolck's Avatar
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    Quote Originally Posted by AZ Hawk View Post
    my point which is that saying a lightweight round is somehow better because it's faster and more energetic is downright ignorant and/or stupid.
    I am not going to continue a conversation with someone who just can't be civil. Seems this forum more than most is full of hostile people if you don't share their viewpoint. Sad.

  5. #20
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    Quote Originally Posted by smolck View Post
    I am not going to continue a conversation with someone who just can't be civil. Seems this forum more than most is full of hostile people if you don't share their viewpoint. Sad.

    Nope, it's not. If you'll reread the sequence of posts in which you participated you'll see that you're projecting again. If you're not going to continue the conversation then why did you just post again?

    It's a forum. Folks have differing points of view. Don't be sensitive. You haven't seen hostile here yet.
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  6. #21
    VIP Member Array glockman10mm's Avatar
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    " You haven't seen hostile here yet" lol, ain't that the truth!

    Kinda reminds me of the phrase in "Next of Kin"
    " You ain't seen bad yet; but it's comin".

    Smolck, just relax. It's all an exercise in thought and and an exchange of ideas. Some guys on here know so much about different topics, that sometimes all I can do is sit back and read and soak it up
    Noone here knows it all, but practical knowledge through the application of trial and error are always something to consider.
    Ignorance is a long way from stupid, but left unchecked, can get there real fast.

  7. #22
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    Sectional density is the amount of material in a bullet from the tip to the base, or in other words, the length of the bullet.
    With all due respect for a very well thought out and written essay, I don't think this is a very good definition of sectional density. Sectional density is in fact the ratio of an object's mass to its cross-sectional area (SD = Mass/Cross-sectional Area). For bullets, CSA = diameter squared.

    SD is a measure of how efficiently an object in motion can/will overcome resistance. All other things being equal (are they ever?), the bullet with the higher SD will overcome resistance (penetrate) better.
    A man fires a rifle for many years, and he goes to war. And afterward he turns the rifle in at the armory, and he believes he's finished with the rifle. But no matter what else he might do with his hands - love a woman, build a house, change his son's diaper - his hands remember the rifle.

  8. #23
    Distinguished Member Array onacoma's Avatar
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    Quote Originally Posted by glockman10mm View Post
    A bullet is made lighter for two reasons; first to give it speed, and two , give it flatter trajectory, which the increased speed accomplishes. Since a flatter trajectory is a mute point for SD purposes, we are left with speed. So what does the increased speed accomplish for us?
    While we normally assume we'll only engage a BG within the 3 to 10 yard training scenarios, one recent event comes to mine. In the Carson City I-Hop one CC permitee was ± 200 feet away from the shooter in his Bar-B-Q store. Now let assume he was willing to take action, he didn't but some may, how close would he have to get to engage the BG? While my 357 sig only pumps out a 125 grain, I can reach out and touch someone beyond the 25 yard mark.

    Training at a 100 yard with a pistol is not very prevalent but one never knows when it will be an asset!

    JMHO


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  9. #24
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    A reasonable explanation from the Hornady site.

    Terminal Ballistics - Hornady Manufacturing, Inc

    "A bullet’s sectional density also affects the amount of damage it can cause. Sectional density (a bullet’s weight in pounds divided by its diameter squared) describes a bullet’s length for its diameter: The higher the number, the longer the bullet. Generally speaking, the larger a bullet’s sectional density, the deeper it will penetrate."

    The narrative linked is primarily discussing terminal ballistics as pertains to hunting but the principle is the same.


    "Sectional density is the amount of material in a bullet from the tip to the base, or in other words, the length of the bullet"

    "SD is a measure of how efficiently an object in motion can/will overcome resistance. All other things being equal (are they ever?), the bullet with the higher SD will overcome resistance (penetrate) better. "


    Pretty much all say the same thing once the definition of sectional density is ascertained.


    I like heavy bullets in handguns. Heavy clothing in the way/ No matter. Pocket book in the way? No matter. Arm bone in the way? No matter. Weird angle? No matter.

    "Trick" bullets that may or may not perform as advertised? Unnecessary.

    It's a trade-out. Ya' can't have everything.
    Cuda66 likes this.
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  10. #25
    VIP Member Array glockman10mm's Avatar
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    OPPFOR, I believe you are referring to Ballistic Coeffiency. How well a design resists air and gravity.
    Ignorance is a long way from stupid, but left unchecked, can get there real fast.

  11. #26
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    Quote Originally Posted by glockman10mm View Post
    OPPFOR, I believe you are referring to Ballistic Coeffiency. How well a design resists air and gravity.
    Nope. Was going from memory since this is something that I've researched, but here's the wiki page.

    Sectional densityFrom Wikipedia, the free encyclopedia
    Jump to: navigation, search
    Sectional density is the ratio of an object's mass to its cross-sectional area. It conveys how well an object's mass is distributed (by its shape) to overcome resistance. For illustration, a needle can penetrate a target medium with less force than a coin of the same mass. When a projectile is in flight or impacting an object, it is the sectional density of that projectile which will determine how efficiently it can overcome the resistance to air or object. The greater the sectional density is for a projectile the greater its efficiency is and therefore ability to overcome the resistance of air and object.

    Sectional density is stated as:


    SD = Sectional Density
    M = Mass of the object, kg or lb
    A = cross-sectional area, m2 or in2
    or for projectiles with a circular cross-sectional area like bullets:


    d = diameter of the circle or the bullet's caliber
    Units are kg/m2 or lb/in2.
    In Europe the derivative unit g/cm2 is also used in literature regarding small arms projectiles to get a number in front of the decimal separator.

    [edit] Use in ballisticsThe sectional density of a projectile can be employed in two area of ballistics. Within external ballistics, when the sectional density of a projectile is divided by its form factor it yields the projectile's ballistic coefficient.[1]

    Within terminal ballistics, the sectional density of a projectile is one of the determining factors for projectile penetration. The interaction between projectile (fragments) and target media is however a complex subject. A study regarding hunting bullets shows that besides sectional density several other parameters determine bullet penetration.[2][3] Only if all other factors are equal, the projectile with the greatest amount of sectional density will penetrate the deepest.
    As noted above, ballistic coefficient is determined by dividing sectional density by the bullets form factor; the form factor being the drag coefficient of the bullet divided by the drag coefficient of a "model" bullet.
    A man fires a rifle for many years, and he goes to war. And afterward he turns the rifle in at the armory, and he believes he's finished with the rifle. But no matter what else he might do with his hands - love a woman, build a house, change his son's diaper - his hands remember the rifle.

  12. #27
    VIP Member Array glockman10mm's Avatar
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    Sounds alot like what I said, except without all the scientific notation.

    Anyway, an elongated bullet profile has better penetrating qualities.
    Ignorance is a long way from stupid, but left unchecked, can get there real fast.

  13. #28
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    But....not really. If it's elongated but hollow, or made of a lighter material, then it's SD will be lower. SD is MASS and (basically) DIAMETER, it has nothing at all to do with length.
    A man fires a rifle for many years, and he goes to war. And afterward he turns the rifle in at the armory, and he believes he's finished with the rifle. But no matter what else he might do with his hands - love a woman, build a house, change his son's diaper - his hands remember the rifle.

  14. #29
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    Quote Originally Posted by glockman10mm View Post
    Seems like lately, there been alot of talkin about lighter ammo vs heavy ammo. As most know, I am a fan of heavy for caliber bullets for all uses. So I figured I'd take a shot at explaining some things about sectional density, weight, bullet construction, and how it becomes a factor in ammo selection.
    ....
    Hope this is helpful to someone....now if I can get Mrs Gman to fill my glass.
    Greater weight has its advantages. No argument there. However, the heaviest non-expanding bullet travelling at > 1000fps is quite likely to go straight through the BG, leaving a .357-sized hole at both the entry and the exit. Yes, he'll probably die. But it might take longer than you want.

    I've cut open enough deer to be thoroughly convinced of the effectiveness of an expanding bullet. Expansion, when combined with adequate penetration, is devastating. Take either factor out of the equation and things are much dicier.

    There's a reason the FBI and many police forces carry expanding bullets.

  15. #30
    VIP Member Array glockman10mm's Avatar
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    Quote Originally Posted by OPFOR View Post
    But....not really. If it's elongated but hollow, or made of a lighter material, then it's SD will be lower. SD is MASS and (basically) DIAMETER, it has nothing at all to do with length.
    This is true. But comparing HP to HP , or like materials, the same remains true.
    Certainly what you say is correct if we compare solid copper construction to lead.

    But the point I was trying to make is very simple, but somehow not easily grasped by some.
    So, to break it down , let's say given two bullets, one lighter, one heavier, same construction and material, the heavier bullet will have better penetrating qualities.

    Bullets constructed of copper retain weight and penetrate very well. Many people pay out the ass for them for these qualities
    But to make weight, they are alot longer than conventional lead bullets of the same weight.
    This can cause issues with available case capacity.

    I am not sure they are worth the extra price when purchasing a heavier option to brand x would have done as well. Better yet, a good ol LSWC.
    Ignorance is a long way from stupid, but left unchecked, can get there real fast.

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