Talk:Terminal ballistics

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I am of the opinion that expanded bullet diameter is essentially meaningless when picking a bullet for a given purpose; the choice should always be made based on penetration, and the diameter is merely a secondary issue. The reason that bullet diameter is often touted is that a cartridge that can push a bullet to the desired depth and expand to a large diameter is going to be a more powerful cartridge than one that hits the same depth with a smaller diameter. Picking a bullet based on large diameter expanded size alone will just get you a bullet that underpenetrates. Bullets may be designed to expand reliably to a certain diameter, but they are also designed to do so at a certain range of velocities, and that implies a certain range of penetration. Be sure that the designers pick the penetration range first, and then design the expanded diameter to match that. Optimum penetration is everything; overpenetration is inconvinent (it can be handled by more accurate shot placement or additional shots) but underpenetration is catastroohic--and there's nothing the shooter can do about it.

scot 18:56, 2 Feb 2005 (UTC)

Expanded diameter is hardly meaningless, because it is a very large factor in both penetration and wounding ability.

In general, the very most important factor is reliability. If the round misfires every other shot, it's not gonna cut it, no matter how great a round it is when it does go off.

Number two is accuracy. If you're consistently missing the target, not even a 16" naval gun is going to produce the desired effect.

Number three is overall suitability to the purpose. A recoilless rifle is great for taking out medium armor at medium range, but against personnel at point-blank range, indoors...

Number four is penetration of the round. For antipersonnel use, the IWBA recommends between 12.5" and 14" on bare gelatin, and 13" to 16" on heavily clothed gelatin. The FBI's guidlines are a more lenient 12" to 18" penetration in all tests.

Number five is expanded diameter. Once the first four requirements are fulfilled, expanded diameter is king. What would work better out of a .357 wheelgun, a fullhouse magnum 158 gr softpoint which expands to double diameter and penetrates 12", or a 147 gr .38 SPL target wadcutter at a leisurly 700 fps, which gives superior penetration of 16"?

Items 1 and 2 are internal/external ballistics issues. Item 3 is a combination of internal, external, terminal, and usability issues, so suitability is dependent on terminal ballistics, not vice versa, so it can be ignored when discussing terminal ballistics in isolation. Item 4, penetration, is dependent on expansion, and you agree to this. The point I was trying to make is, I think, the same as yours, although perhaps I didn't state it with sufficient clarity. Penetration is the #1 most important issue when dealing with terminal ballistics in soft targets. Once you hit the desired penetration depth, then expansion is a good thing, because then you are doing the disruption in the vital areas, and not wasting energy by exiting the target. Your .357 vs. .38 comparison is applicable, but only because the FBI reccommended minimum is sufficient to traverse a human chest cavity from any reasonable angle. 6 inches of penetration is generally enough;

Far from it. What everyone forgets to mention about jello testing is that skin has a far, far greater tensile strength than the muscle which calibrated gelatin simulates. Human torso skin resists penetration by projectiles as much as 2" of muscle/gelatin on the entrance side, and as much as 4" on the exit side. Horse skin resists penetration as much as 8" of horse muscle (probably the equivalent of 10-12" gelatin) on entrance. A rib, or the skull (of a human), adds approximately 2-4 more inches. So a penetration of 6" would not even be guaranteed to puncture a lung, if it hits a rib or the sternum. Assuming the heart is located about 1" behind the sternum, a bullet would need 8-9" of penetration just to to puncture the heart on a perfectly placed frontal torso shot. Arrkhal 19:22, 4 Feb 2005 (UTC)

would you want to bet your life on a bullet that penetrated to, say, halfway between 6 and 12 inches? I wouldn't. In fact, I'd pick a .22 LR solid over a frangible .357, because that .22 will go in far enough to do vital damage, while that .357 might fail to penetrate a thick layer of colthing and/or fat. On the other hand, I certainly would choose a .357 that penetrated 12" over a .22 that penetrated 12" (assuming recoil and firearm size (suitability to purpose) allowed the bigger caliber). Now if I'm given a choice of bullets that, with the same muzzle energy, penetrate 12" vs. 60", I'd definately go with the 12" penetration bullet if 12" is beyond my minimum requirement. If my minimum requirement is 16", however, I'm not going to trust the bullet that penetrates 12"; I'll go with the 60" of penetration and live with the attendent loss of energy.

What really determines the hole size is pressure, which is much more a factor of bullet shape than of energy, and it's very possible for a deep penetrating bullet to be efficient enough to crush an equivalent hole.

For instance, let's say a handloaded 147 gr LHBWC at light magnum energies penetrates 30". A heavily loaded 180 grain flat-point with the same energy penetrates deeper. Now, the 180 grain would have lower pressure on its tip, but it would still be more than enough PSI to crush a hole which is the diameter of the entire meplat, for most of the penetration depth. The 147 gr bullet might generate more temporary cavitation, but that doesn't have much of an effect at lower than 2,000 fps for fragmenting softpoints, or 5,000 fps for nonfragmenting rounds. Arrkhal 19:22, 4 Feb 2005 (UTC)

This is why dangerous game bullets, which are expected to be used on difficult frontal shots, are either solids or very limited expansion bullets, and whenever possible fired from hugely overpowered guns--you do NOT want to underpenetrate when a Cape Buffalo is trying to mash you into jelly. scot 17:08, 4 Feb 2005 (UTC)

Part deux (not a response to previous post)

For those of you in the energy transfer crowd, I strongly recommend reading "my" article on stopping power. "Energy transfer" is pseudoscience. All it is is a buzzword. It does not adequately describe the process by which bullets wound. Not one bit.

"Energy transfer" is physics. If a bullet enters with velocity X and leaves with velocity Y, then difference in the amount of momentum or energy is the amount of energy that is tranferred to the target, as impulse, heat, tissue damage, or what have you.

The problem with that kind of reasoning is that momentum and energy are "transferred" differently. Momentum is always conserved as momentum. Always. The kinetic energy which "tags along" with the momentum is conserved as KE, but it never exceeds the momentum. Will a bullet with 500 ft-lbs of energy really kick a 1 pound lead block 500 feet? Of course not. The acceleration on the block is going to be a product of momentum transfer, with some KE being conserved (in the momentum of the block+bullet), and the rest being "lost" as heat, noise, deformation, etc. Deformation is hard to put a figure to, though, since it's dependent on both the momentum and the energy level. Arrkhal 19:22, 4 Feb 2005 (UTC)

If energy transfer is entirely irrelevant, then you should be able to design a bullet that kicks like a .22 Short and hits like a .44 Mag--but you can't, because wounding requires energy.

No problem. Imagine a hydrofoil type "bullet" made out of 3/4th inch diameter tubing with 1/32nd" thick walls, .5" high. Frontal surface area is 0.0706 in^2, comparable to a .3" wide bullet (so a .29 caliber, if such a thing exists). If it's made of steel, mass is a mere 69.6 grains. It penetrates to the same depth as a .29 cal, 69.6 grain wadcutter with the same velocity on it. But, because of its construction, it effectively makes a perfect, 3/4" wide hole for the entirety of its penetration depth. Even a .44 magnum which expands to .75" won't make a .75" hole through most tissues, because the rounded shape allows some tissue to flow around it, relatively unharmed aside from minor stretching damage. Arrkhal

From the other direction, flechette guns haven't been adopted because while they have phenomenal external ballistics, they pass right through their target with little loss of velocity, and thus have don't transfer sufficient energy to wound (the SCIMTR round being the significant example--it was designed to cut a wide path through the target--and because if that, it slows more or stops in the target). scot 17:08, 4 Feb 2005 (UTC)

Actually, flechettes had lousy external ballistics for their intended purpose; combat in dense jungle cover. They worked fine out in the open, but a single leaf, or even a raindrop, was usually sufficient to destabilize them due to their low mass.

In that case, though, it's still not "energy transfer." It's pathetically small hole size. A 1 pound ice pick stabbed into a person at some velocity loses the exact same amount of energy in the target as a 1 pound dagger at that velocity. The effect is different, despite identical energy levels, because the dagger makes more efficient use of pressure, spreading it out along a wide cutting edge. Arrkhal 19:22, 4 Feb 2005 (UTC)

Do you seriously believe that there's some magical "energy" factor which makes one bullet which expands to X and penetrates Y significantly better than another, lower-energy bullet which also expands to X and penetrates Y?

Beleive, no. Suspect, maybe. I don't think the "hydrostatic shock" people have proven their point, but I think there are a number of cases of instant incapacitation that aren't completely explained by hemorraging and blood pressure loss.

Those are very easy to explain. Psychological shock, and CNS trauma.

"Oh my god, I've been shot!" is enough to cause many people to faint. It's an extremely well-documented phenomena, that sometimes suspects who are shot in the arm, leg, or even missed outright, often pass out on the spot.

Animals don't faint, however, and sometimes people collapse without fainting, too. That's due to CNS damage. A bullet which impacts the spine or cranium and punches through will likely cause instant unconsciousness, followed by death due to blood loss or neurological damage. If it hits the spine or cranium and stops, it still likely causes enough blunt trauma to knock out, stun, or paralyze the target. Similarly, if a bullet with massive temporary cavitation passes close by the spine, the rapidly-moving tissues surrounding the spine can whack into it hard enough to generate a stunning effect. Arrkhal 19:22, 4 Feb 2005 (UTC)

Personally, I keep a Mossberg 500 12 ga. under the bed, under the theory that a whole lotta little 12" deep holes from solid balls are better than one or two bigger holes from a hollow point that may or may not expand if I have to shoot through sheet rock, leather, or any of the myriad other substances that tend to clog hollow points and prevent them from expanding. (And just in case you think I weasled out on the issue, the backup to that is a .45 ACP loaded with 230 gr. HydroShocks, so I do put more trust in the big and slow school.)

Buckshot is a great choice for close range stuff. Sounds like you're using #1 shot, since that stuff penetrates in the 12"-13" range. If it's something else, I recommend switching to #1. #4 and #1 exhibited identical penetration through wallboard, while 00 penetrated an extra wall or two.

I strongly recommend against Hydra-Shocks, though. Unbiased, 3rd party testing shows that the central post does nothing to prevent clogging of the hollowpoint cavity due to wood, metal, clothing, etc., and the 4-layer IWBA denim test causes every single Hydra-Shock in every single caliber to fail to expand, always. No, bad guys usually aren't wearing 4 layers of denim, but they can get pretty close. 1 leather or denim layer of coat, 1 inner cloth layer of coat, 1 tee-shirt, and 1 undershirt make 4 layers.Arrkhal 19:22, 4 Feb 2005 (UTC)

All else being equal, the higher energy bullet will have to be of lower mass to perform equally to the lower energy one, which means it has a higher initial velocity, and higher retained velocity for most of its travel. Higher velocity gives fluid tissues less time to "flow" out of the bullet's path, thus a higher velocity increases crush efficiency. Higher velocity also gives the bullet more momentum (Not energy. Try looking up some high school level physics. Transfer of momentum is what causes movement as a result of impact.), so more momentum is transferred to tissue in the form of temporary cavitation. This increases the crush efficiency and temporary "stretch" cavity diameter by an amount roughly proportional to the increase in velocity. But that's it. That's the only effect of increased energy on a given expansion and penetration performance.

Yes, I've taken physics, in both college and high school. I wrote, from basic physics and chemistry principles, the internal ballistics simulation software that I used to generate the charts for the internal ballistics article. I understand momentun, and viscosity (which, combined with momentum, gives the penetration depth), and energy, and elastic and inelastic collisions. As for temporal cavities, I have yet to see a convincing explanation of exactly what impact they have on wound ballistics, complete with charts, extrapolations of temporal cavity vs. hemorraging speed, etc. that will let me put any trust in the temporal cavity.

That's because temporary cavity is practically irrelevant, as you've guessed. While a jello-block with a huge hole in it filled with red dye certainly looks impressive, it doesn't do much at handgun velocities. A fragmenting bullet which retains 50% or more of its mass, and is moving faster than 2,000 fps, though, is able to tear living tissues slightly. The fragmentation weakens tissue significantly, which allows the temporary stretch to tear it. Nonfragmenting bullets, however, don't actually tear tissue until their velocity exceeds 5,000 fps.Arrkhal 19:22, 4 Feb 2005 (UTC)

I've even done some research in forensic medicine. Once you read the account of the guy who took out most of his cereberal cortex with a .45 ACP under the chin, then walked around for 3 hours in a lucid state before lying down and finally bleeding to death, you don't take any theory involving wound ballistics to heart unless you see a gob of information to back it up. scot 17:08, 4 Feb 2005 (UTC)

That sounds like the one about the domestic violence incident in which the boyfriend or husband or something shot a woman square in the forehead with a 158 grain .357 magnum semi-jacketed hollowpoint. The bullet went right between the lobes of her brain, splitting them (but inflicting no other damage), and exited out the back. Didn't even knock her out, but she did have a terrible headache. A lot of the brain isn't particularly vital for continued function of the body. Basically, anything which doesn't take out the brain stem or cervical spinal cord (directly, or indirectly via oxygen starvation via blood pressure loss) isn't 100% guaranteed to put a person or animal down.Arrkhal 19:22, 4 Feb 2005 (UTC)

Energy also does not correlate whatsoever with penetration depth. Too many people believe that energy and penetration depth are proportional. Try this simple experiment. Inflate a balloon, then throw it at modest speed. Note how far it travels. Now throw the balloon roughly twice as fast as you did the first time. Doubling velocity quadruples energy. Did the balloon travel 4 times as far as the first throw, or did it travel closer to 1.5 or 2 times as far?

Energy is not what gives you penetration, momentum vs. viscocity is, with a bit of fiddling for aero/hydrodynamics (which mainly has to do with how fast the fluid must be accelerated past the contours of the object--so back to momentum and viscocity). If energy were the only concern, we'd be using lasers--zero momentum and the maximum amount of energy allowable by physics as we know it. scot 17:08, 4 Feb 2005 (UTC)

Well, police agencies are using tasers quite a bit now. Lots of energy, but very little momentum. In seriousness, though, the correlation between momentum and penetration is also pretty close to nil, given the linear correlation with mass, and logarithmic correlation with velocity. Halving mass and doubling velocity results in reduced penetration, while doubling mass and halving velocity results in increased penetration.Arrkhal 19:22, 4 Feb 2005 (UTC)

Actual correlation between energy and penetration is nil.

Only if you claim that the correlation between energy and momentum is nil, and it's not, especially when you consider that you have a limited mass range to work with. By the "energy doesn't matter" arugment, you're better off lobbing a 16 lb. chunk of rebar at the 1.8 fps than a 230 grain bullet at 900 fps.

Momentum on its own isn't that great, either, especially when pressure is insufficient to penetrate.Arrkhal

If we ignore energy, then they should penetrate the same amount, but the don't.

Correction: if we ignore energy and pressure, they would penetrate the same amount. In a medium in which pressure does not matter, and in the absence of gravity, the penetration would be roughly equal. In most mediums, though, like water, increased pressure at increased velocity causes diminishing returns (logarithmic correlation) on velocity increases.Arrkhal 19:22, 4 Feb 2005 (UTC)

Energy is the ability to do work--and work is what is required to cut through tissue. Where that energy is applied (i.e. what tissue you cut) also matters, and so the energy, momentum, penetration, and diameter of the bullet must all be sufficient to cut the amount of tissue you want after penetrating to the depth you want. If any of the 4 elements are inadequate, then the bullet will fail to have the desired terminal effect scot 17:08, 4 Feb 2005 (UTC)

We basically agree on this, it's just you're saying it's ft-lbs, and I'm saying it's PSI.Arrkhal 19:22, 4 Feb 2005 (UTC)

Correlation between mass and penetration is directly proportional. Correlation between frontal area and penetration is directly proportional. Correlation between velocity and penetration, however, is logarithmic.

Mass and penetration, for a given velocity, are linearly proporitonal. Frontal area and penetration, for a given mass and velocity, are inversely linearly proportional. If momentum (mass times velocity) is the only concern for penetration, as you seem to imply above when you say ""Energy transfer" is pseudoscience", then penetration ought to be directly linearly proportional to velocity. Since you claim it is logrithmic (I'll agree to the rough shape if not the exact function that generates it--I doubt it's that simple) then penetration vs. energy, for a given mass and frontal area, are going to vary pretty close to linearly. scot 17:08, 4 Feb 2005 (UTC)

Putting energy into a graph instead of velocity still results in a logarithmic curve; one which goes up even slower. Unfortunately, fluid dynamic interactions involving velocity changes are far too complex to model with a single equation; the higher the velocity, the faster it loses velocity, due to increased pressure and drag.Arrkhal

For instance, the penetration of .45 caliber, 230 grain hardball is very accurately modeled by the equation Y = 22.5 * Ln X - 126. Y is inches of penetration into 10% gelatin, and X is striking velocity in feet per second. Within the 700 to 5000 fps range, it correlates with calculated data greater than 99.99%. Below 700 fps, correlation drops off rapidly. Because of the correlative properties of the other factors, this equation can be used to calculate the penetration depth of any FMJ or LRN bullet which is shaped the same as .45 hardball.

See above--log approximates the curve (I won't buy the source that gave you 99.99%, real data is NEVER that precise) so there's an infininte number of x^n functions that will approximate it over the given range as well. scot 17:08, 4 Feb 2005 (UTC)

It wasn't "real" data, of course. It was data obtained from a slightly flawed (doesn't seem to account for drag differences at different velocities) calculator, which I then graphed myself. It seems pretty darn accurate aside from the drag issue, though. http://home.snafu.de/l.moeller/Penetration_Calculator_2.html Arrkhal 19:22, 4 Feb 2005 (UTC)

Now, if anyone can explain how a greater amount of energy somehow magically enhances a given bullet's performance aside from the modest increases in crush efficiency and temporary cavitation, I'm all ears. The catch is, it has to involve actual science. "The bullet with more energy wounds more due to energy dump" or similar unreasoned are wholly insufficient.

But the question is, given 12" thick block of gelatin, does the 5000 fps. bullet wound more than the 700 fps bullet? The slower bullet will still penetrate over 20" give your formula, so both meet minimum penetration requirements. The 5000 fps bullet is going to lose FAR more energy passing through the block and that energy must go SOMEWHERE, if you aren't to violate the laws of physics.

Heat, vibration, noise, deformation. But from what I've seen, most of the difference correlates closer to momentum and pressure differences than to energy differences. In other words, doubling a velocity tends to produce twice as much of an effect, rather than four times as much.Arrkhal 19:31, 4 Feb 2005 (UTC)

The reason it loses more energy is that the 700 fps. bullet must accelerate the gelatine at (and this is a WAG) about 330k Gs upon impact to move it sideways enough that the bullet can pass through. The 5000 fps. bullet will have to do it at 1.6M Gs. That's 5x the acceleration, which means 25x the energy to create that acceleration. That energy is transferred from the bullet's velocity into the gelatine, where it has to go somewhere. It goes into heat, and at 5000 fps you're definately going to be generating enough heat upon impact to vaporize some of the gelatine, and the shockwaves and going to just disintegrate the block.

That's not the case with living tissue. I have a PDF of an article by Dr. Martin Fackler, on his tests with super hypervelocity bullets in very freshly-killed (before any loss of muscle elasticity or stiffening due to rigor mortis could occur) pig buttock tissue.

He used a custom-made gun which fired .224 bullets from the powder charge of a .50 BMG. At ~4,000 fps, most bullets did not perform very spectacularly, creating about a 1" diameter hole with slight radial tearing. At 5,000 fps and up, however, flat-nosed rounds generated enormous amounts of tearing, about a 5" diameter hole, though that might have partially due to the solid brass bullet fragmenting at that point. A 5,000 fps pointed bullet, however, generated a very small, puncate entrance wound, but significant tearing deeper in where the bullet tumbled.

I imagine heating damage is going to be minimal. A 230 grain bullet at 5,000 fps has 17,303 joules of energy. A 1" x 1" x 66" rectangular prism of gelatin (1,084.5 cm^3) which captures the entire wound track would be heated by 16 degrees C, assuming that 100% of the bullet's kinetic energy is converted into heat, and that the specific heat of jello is the same as water (1J/1degC*1gram).Arrkhal 19:22, 4 Feb 2005 (UTC)

Now at what point this heat energy has a significant impact on wounding I don't know, but I've blown enough 2 liter plastic bottles full of water into tiny bits of shredded plastic using a .223 Remington JHP to know that that energy does have a significant impact (if you'll pardon the physics pun) on the target. scot 17:08, 4 Feb 2005 (UTC)

My understanding of fluid dynamics is that it's actually momentum transfer which causes inelastic, fluid targets to "explode."

Heating due to energy transfer was a popular theory in the 19th century and before. People believed that all lost energy was converted into heat, which boiled away flesh into steam and melted the bullet; hence, a high velocity bullet had a deformed, "melted" appearance, while a low velocity bullet was mostly intact. Similarly, bullets which hit rocks and other objects were heated faster due to the shallower penetration and more rapid energy transformation, thus they splattered even more. This was disproven in the early 1900's.

Once rifled muskets were common, a second theory arose which stated that the angular velocity of the bullet is what causes most of the temporary cavitation type damage (exploding watermelons and the like). I'm not sure when this was disproven, but bullets most certainly continue to spin after penetration, usually at almost the same RPM as when they entered.Arrkhal 19:22, 4 Feb 2005 (UTC)

I should start an "energy transfer" page. Actually, I think I will!

[edit] Large caliber terminal ballistics

Does anyone have any references to back up the following assertion?

Contrary to popular belief, the copper cone is not substantially heated, nor melted. Rather, the massive force of the explosion is sufficient that the metal behaves like a fluid while still technically in a solid state.

As a chemist, I have trouble wrapping my mind around how a solid can behave like a fluid. I guess one could argue some kind of non-equilibrium affect, but right now I am not buying this. I will take the liberty of removing the above text unless someone can provide more information.Rangek 23:24, 2005 May 2 (UTC)

Well, if you look at the dynamics of a system, the way a piece moves is affected by its momentum and by the forces on it. If the momentum is far greater than the forces on it, then the forces don't make much difference in how it moves. So if you have a sufficiently high-speed collision, the attractive forces between atoms are irrelevant compared to the momentum of the atoms. The repulsive forces, on the other hand, increase as much as necessary as the thing compresses. If you like, you can think of it as "...behaves like a powder" or "...behaves like a plastic", since all those things behave the same at these speeds.

This isn't a great answer. Let's see if someone comes by with a better explanation. --Andrew 00:08, May 3, 2005 (UTC)

When the kinetic energy is high enough that atoms/molecules move around the system (i.e., the particle-particle interactions are not big enough to keep them relatively fixed), then you have a fluid. Right?Rangek 16:54, 2005 May 3 (UTC)

Well, that's one way to put it, but you have to distinguish between random kinetic energy (heat) and bulk kinetic energy (motion). If either one is high enough, the material strength is irrelevant and the thing behaves like a fluid, but it's not really a fluid unless it's heat that does it. --Andrew 19:47, May 3, 2005 (UTC)

If the particle-particle interactions are large enough to keep the particles relatively fixed then you have a solid, regardless of the velocity of the system's center of mass. I.e., a slug of lead traveling at 99c is still solid. Now if that solid slug hits something, I am guessing neither it, nor its target will be solid for long. Rangek 03:27, 2005 May 4 (UTC)

http://www.logwell.com/tech/shot/perforator_life_cycle.html

I know of a much better article than that, which included an animation of the temperature of the "jet" at different times (and at no time did the temperature of the "jet" exceed the melting point of copper), but I've yet to track it down. I'll keep looking. Arrkhal 23:01, 3 May 2005 (UTC)

Oh. Oops. That article is linked to right at the end of the terminal ballistics article, though not cited. http://pegasus.me.jhu.edu/~molinari/Projects/Shape/SLIDE-1.html

The melting point of copper is 1356 degrees K, and according to the diagram, most of the copper "jet" is ~1040 degrees K, while the hottest portions, near the center, reach ~1140 degrees K. Arrkhal 23:05, 3 May 2005 (UTC)

Cool, stuff. But nothing there says that the jet is a solid. That melting point is probably at 1 atm. How does copper behave at 1000 K and 1 million psi? I mean, heck, even the term "jet" itself implies fluidity. I think a link to rheology would be relevant, perhaps. At any rate, I still think that the phrase "while still technically in a solid state" is incorrect. Rangek 03:27, 2005 May 4 (UTC)

At sufficiently high speeds, the hardness of a solid becomes essentially irrelevant, as the inertia provides nearly all the resitance to deformation--this is why, say, a lead bullet hitting a steel plate splashes. At those speeds, the hardness of lead is so small as to be irrellevant, and the force of impact deforms it just as though it were a liquid. The same principle would apply to a shaped charge, the liner would be forged into a rod and "squirted" out into the target by the converging pressure waves. Under forces and timescales like that, the terms "solid" and "liquid" really have no meaning. scot 18:36, 4 May 2005 (UTC)

I believe your statement: "under forces and timescales like that, the terms 'solid' and 'liquid' really have no meaning" is true, and therefore the phrase "while still technically in a solid state" is incorrect. I will remove it.Rangek 18:42, 2005 May 4 (UTC)

You might point out that density is more important than hardness in KE penetrators. Or rather that as speeds increase, hardness basically drops out of the equation. My physics/engineering math isn't quite up to figuring out just how fast that happens, but hardness is a constant while intertial forces increase with speed and density, and I have seen low velocity lead splash off steel while high velocity lead punches right through. scot 19:14, 4 May 2005 (UTC)

'At any rate, I still think that the phrase "while still technically in a solid state" is incorrect.'

Why? It is still solid, but the massive forces involved cause it to behave plastically. Modelling clay is also able to be squeezed and squished into various shapes, potentially at very high velocities if large forces are involved, but is still "technically in a solid state." The molecules will not appreciably diffuse to fill a container; it won't flow to conform to the shape of a container; it sits there in a fixed shape until a force acts on it which exceeds its elastic or shear moduli; so solid it must be. It's just modeling clay is deformed much more easily than copper. Arrkhal 03:05, 7 May 2005 (UTC)

I'm going to change the statement made by 217.43.6.65, which is a follows:

"The current NATO 5.56 mm SS109 bullet does not use a steel core to improve penetration, but a heavier 69 grain bullet. This heavier bullet results in an increased sectional density improving penetration."

This is very much false; while the greater sectional density does lead to greater penetration, the steel tip is there specifically to resist deformation and improve penetration of hard armor. The steel tip makes the SS109 quite unstable, as it makes it even longer and more back heavy than anything less than an 80 grain ultra-low drag bullet. This high instability requires a fast barrel twist (the military uses 1 in 7, you can get away with 1 in 10 for short range) and fast twist barrels tend to wear faster. If sectional density were the only goal, they could shoot an 80 grain VLD (very low drag) bullet, and stretch the range of the 5.56mm out quite a bit further--more so than even a standard military 7.62mm load. Current shooters shooting the 77 and 80 grain 5.56 are actually outshooting the tried at true 7.62mm rounds at distances beyond 300 meters, a feat long thought impossible. In fact, the 1000 yard matches at Perry have been won by an AR-15, 1 in 7 twist, firing 80 grain low drag bullets, which are still supersonic at 1000 yards! Blew the 7.62mms away, since they had to deal with the effects of dropping subsonic before the target. While you could scale the bullet design up and get a 7.62mm to do subsonic out to 1000 yards, it's going to be one heck of a massive bullet. Switching to an 80 grain VLD isn't practical for the military however (excepting maybe snipers) at the moment; the 80 grain VLD requires a dense core, so a steel tip is out, but tungsten might just be the key. Depends on which direction the military goes when they phase out lead bullets; if they go with a higher density, high strength material like tungsten, then the VLD design becomes quite practical. If they go with something like bismuth, then they'll still need a hardened tip, and hitting the 80 grain mark may be impossible with practical twist rates. scot 15:18, 11 July 2005 (UTC)

OMG! The products of the American public school system... faith based science where energy is irrelevant and momentum matters (!!! Dude, a 9mm bullet has the momentum of a volleyball falling 30 meters or something like that, oops that's 100 feet for you. Anyway, let's make a little experiment, you drop a volleyball from 12th floor and I'll catch it down in the street, and then we switch positions and I'll shoot at you from the 12th floor and you try to catch the bullet. Sounds like a plan?) Punching a hole into some material requires energy. Removing material requires work. This is 7th or 8th grade physics (at least where I come from) and the laws of nature still apply. Unfortunately some mystical unexplainable stopping power that nobody can describe anymore since granddad died 10 years ago is not relevant. I have no doubt everyone still immediately recognizes these magic bullets filled to the brim with mean, pure, unadulterated all-Americann stopping power when they see them (no doubt some .45ACP or similar would qualify) ... hydrashhock bullets rock!!! (actually can not expand since they are traveling too slow for that)...What else? oh yeah, temporary wound cavity doesn't matter! Well dude, if someone drives a scredriver all the way through your thigh and then proceeds to tear the exit wound about 4 inches wide followed by inserting a knife into the wound channel to convert a pound of your muscle into hamburger meat which is then forcefully removed from the wound and liberally spread all over the next wall leaving a horribly shredded hole all the way through your thigh and lots of blood shooting out of the destroyed and badly torn vessels, would that make you change your mind?

All rifle bullets tumble and eventually turn around inside the target if they are given the opportunity. How deep they will penetrate straight before turning around or even disintegrating(creating the wound cavity in the process) depends on several factors including speed, what kind of tissue is hit (hard obstacles or not?)

First, reguarding units, I work in English units where ballistics are concerned because the information available to me is in English units--those Hydra-Shok bullets, you'll note, are 230 grains, not 14.9 grams. And for the purposes of penetration, energy is irrelevant; the distance penetrated is a function of mass times velocity divided by the frontal surface area. The reason said volleyball doesn't penetrate as far as a 9mm is because the volleyball has 331,662 mm^2 of frontal surface area, compared to 63.8 mm^2, so the force is spread over 5200 times the surface area. A valid comparison would be an arrow with a 9mm diameter point; the frontal surface is the same, the mass is much higher and the velocity much lower which will cause a great disparity in energy and momentum.

I found a hand-dandy website that, ironically enough, takes the same view you do--kinetic energy is what matters for penetration. Hers's the link: http://www.bowsite.com/bowsite/features/practical_bowhunter/penetration/index.cfm I'll takes some choice quotes from there and see what we can do. A quote from the site:

"According to Easton, a 400 grain arrow traveling at the glacial speed of 170 feet-per-second has sufficient energy to harvest a mature deer. Heck, many kids bows can easily shoot such a light arrow faster than 170 fps, and I’ve seen such rigs do pass-throughs on deer!"

So that's a 25 ft-lb arrow, passing through a 12" thick deer--12" is the FBI's minimum penetration requirement, so that's a perfect minimum for us (that's 34 joules and 34 cm). Now, if we convert that to the velocity required to launch a 29 grain bullet (that's what a .22 Short uses) we get 631 f/s, which is about what you'd expect out of a .22 Short in a 2" barrelled gun. So are you going to go deer hunting with a .22 Short? Admittedly, the .22 Short was developed by S&W for their first pocket revolver, but current though is that the .380 ACP at 130 ft-lb is the absolute minimum for self defense use, and many put it up over 200 ft-lb. The same site says 65 ft-lb is the minimum for Cape Buffalo and grizzly bears; that's still less than a .22 Long Rifle.

Now let's look at the other side--what does it take to get the same momentum as the arrow? Let's do the easy math, and calculate for a 40 grain bullet. That would mean 1700 fps, which is about what a .22 WMR would produce. Yet the .22 WMR, if it mushroomed out to 9mm diameter (not unlikely with a good hollow point) would be hard pressed to penetrate anywhere near 12 inches. Here's where sectional density steps in--to have the same sectional density as our 400 grain, 9mm arrow, the bullet would need to be .11 caliber, a 4x increase in sectional density.

If "a pound of hamburger meat" is removed, that is a permanent cavity, not a temporary cavity. The temp. cavity is the amount the tissue stretches and then rebounds (that's why it's temporary). The resulting cavity after stretch is the permanent cavity. As for temporal vs. permanent cavity arguments, I think they're both wrong, or rather half right. A punch in the stomach generates a fist-sized temporary cavity, yet a death from such a punch is rare except in the case where the stretching causes significant damage to a major organ--for example, the ruptured appendix that killed Harry Houdini. A permanent cavity, however, involves the tearing of tissue, which opens blood vessels and allows bleeding. Once again consider the case of the arrow--the permanent cavity from an arrow wound is almost nonexistant, as the flesh seals right up after the passage of the arrow. However, the cuts left by the arrowhead still bleed, and can cause death quickly. The cut surface is what is important here, as that is what allows the bleeding that is the debilitating factor in most arrow wounds (shots to the blood vessel rich heart/lung area provide the fastest bleed-outs, due to the large number of vessels and the fact that the lungs have area to bleed into). I think the critical factor for a non-critical hit is a combination of the number of blood vessels opened by the bullet's passage, and the amount of bloodloss that the remaining permanent cavity allows. If the temporal cavity ruptures organs, then it would certainly have a significant impact, but on more flexible tissue like skin and muscle, the impact would be significantly less.

Reguarding tumbling rifle bullets, the statement that "all rifle bullets tumble eventually" is false; only bullets whose center of mass is significantly behind their center of lateral pressure have enough yawing force to overcome the stabilizing effects of the bullet's spin and tumble. Large bore bullets are often too stable to tumble, but most .30 caliber and lower bullets with long, sharply pointed noses are quite unstable. A marginal spin also helps the tendency to tumble--for example, the early AR-15 rifles had a twist rate barely adequate to stabilize the inherently unstable pointed bullet, and so it would tumble almost immediately on impact--unfortunately, it would also tumble in the air at long range. Devastating at close range, it couldn't hit the target at long range (it was designed for a 300m max range). With a faster twist rage, the accuracy improved, but the lethality went down since the bullets didn't tumble as fast, and would often pass right through. The SS109 would be much more stable if solid lead or steel, but the steel tip makes it backheavy, decreasing stability even more, so it tumbles quickly, but fragments at the cannelure (which is also the lead/steel junction and thus quite weak) as soon as it turns sideways. The two fragments each tumble through the target and create separate wound cavities. Since the surface area of the two halves is greater than the surface area of the single bullet, the total temporary and permanent cavities are larger, plus the divergent paths increase the probablility of a hit on a critical organ.

And as for catching 9mm bullets, sure, but I should warn you that my theory on gunfights is that if you're planning on going to one, the correct course of action is to stay several hundred miles away and use a cruise missle... scot 23:08, 2 December 2005 (UTC)

I know nothing about guns or ammunition, but came to this article from the ballistics gel article, which I was reading for fun. The current article is very poorly organized and very technical. I would advocate putting a "This article needs to be edited" tag on the front. 67.9.131.227 19:34, 8 December 2005 (UTC) Reuben Grinbeg

I took a look, and it seems to me to be laid out fairly logically--of course, I wrote the bulk of the aritcle, so maybe it's just laid out the way I think. If you have any specific suggestions on what sort of formatting might be better, and what sort of information needs to be added, I'd welcome them. For example, if you have just a passing interest, would an "executive summary" at the start of the article, that just hits the basics in broad terms, be helpful? And if so, what sort of things would you like to see in the summary? scot 20:33, 8 December 2005 (UTC)

Scot I am the guy who brought up the public school system comment, and I want to apologize. I still disagree with you though. 1. Reguarding tumbling rifle bullets, the statement that "all rifle bullets tumble eventually" is false; only bullets whose center of mass is significantly behind their center of lateral pressure have enough yawing force to overcome the stabilizing effects of the bullet's spin and tumble. Large bore bullets are often too stable to tumble,

All bullets have the center of pressure behind the center of mass, otherwise they wouldn't fly very well even when spinning. Once the bullet enters another medium with a much higher density the center of pressure shifts dramatically, that's why all fast non-blunt rifle bullets will turn around eventually unless they expand. Some just take a lot longer than others.

While it is true that most bullets, even short, fat handgun bullets are backheavy to some degree, not all are, and the ones that are front heavy are by far the most stable. Hollow based wadcutters, most airgun pellets, and especially Foster slugs are all very front heavy, and they are the most stable of bullets--Foster slugs are even stable from smoothbore barrels, with the thin, hollow rear of the slug acting like a shuttlecock and providing aerodynamic stability. Even these will tumble in the target, but only under extreme conditions, such as an oblique impact. And as to modern boattail spitzer bullets tumbling, they don't always--as a matter of fact, the Swiss deliberatley re-engineered the bullet used in their service round to prevent tumbling, and thus reduce the lethality of the bullet.

2.The reason said volleyball doesn't penetrate as far as a 9mm is because the volleyball has 331,662 mm^2 of frontal surface area, compared to 63.8 mm^2, so the force is spread over 5200 times the surface area.

If your theory is correct that penetration depth depends on impulse per frontal area then this will revolutionise impact physics, metal manufacture, accident research and what not. I think the last 200 years of published physical literature prove you wrong. Chopping some wood will do the same, btw. A slow arrow will cut through the meat, or move through flesh like a boat through water. A slow handgun bullet will crush the meat in its path but won't do much to the surrounding tissue. A fast rifle bullet will cause a big temporary cavity, and when you believe that tissue stretched at several hundred meters per second will not damage vessels and nerves then you are wrong. These are three totally dissimilar modes of action, and trying to unite them under "one (i.e. my favorite) explanation fits all" is very very questionable. No more faith based science please.

Well, actual research into wound ballistics done by the FBI seems to show the temporary cavity is of little importance. To quote:

"Kinetic energy does not wound. Temporary cavity does not wound. The much discussed "shock" of bullet impact is a fable and "knock down" power is a myth. The critical element is penetration. The bullet must pass through the large, blood bearing organs and be of sufficient diameter to promote rapid bleeding." http://www.thegunzone.com/quantico-wounding.html

Penetration is a factor of how much tissue the bullet can move out of its way as it pentrates, and how much energy is required to move said tissue. A fat bullet must move more tissue, so the penetration is inversely proportional to surface area. A fast bullet must move the tissue at a higher rate, which uses more energy than a slow bullet moving the same amount of tissue. Since the rate the tissue must move is a function of velocity, a bullet moving twice as fast must expend twice the energy to accelerate the tissue away, thus it slows down faster. Yes, it is the energy that does the work, but doubling the velocity doubles the energy required to penetrate, so you're back down to a linear function of penetration vs. velocity. I've done the math (years ago), and what I came up with was that penetration was a function of kg / (m * s) which is, not coincidentally, the unit used to measure viscosity. Take that kg / (m * s) and multiply it by velocity / velocity and you get (kg * m / s) / (m^2), which is what I maintain is the base equation for penetration--momentum divided by frontal surface area.

I'm not saying the is the end-all and be-all of penetration calculations, as it does not take into account shape at all, but it should allow relative comparisions of similarly shaped bullets. Flat pointed bullets will penetrate less, as they must accelerate the tissue much faster to push it out of the way, while spitzer bullets will penetrate deeper since they accelerate the tissue much less.

I'd like to check your calculations and show you where you went wrong, but unfortunately I cannot make much sense out of those units (at least not at 3am in the morning). Let's just say I'd be willing to catch that volleyball even if it had a 9mm iron bolt through the middle sticking out for an inch or so.

Have at it based on units, then, and see what units you end up with in the end. I'll bet if you break things down into mass, distance, and time, you'll get the same results. As for the volleyball, I think you might be right on that; I show a 210g volleyball at about 13 m/s being the equal of a 9.5g bullet at 290 m/s. I think the issue there is there's not enough energy to generate a "temporary cavity" 9mm in diameter. Maybe if the bolt tapered very gradually from 9mm down to a needle point, you'd get some penetration, but then surface drag would start to play a major role... At any rate, even at airgun velocities of 150 m/s, the projectile has enough energy to generate a significant temporary cavity; wax is ideal for observing this, since it's not elastic and shows you the full diameter cavity generated by impact (pneumatic airguns are great for this, you can watch as increased velocities gradually increase the crater diameter). Hmmm, maybe that's where the viscocity comes in, the temporary cavity has got to be related to viscosity, don't you think? scot 06:17, 16 December 2005 (UTC)

Actually, no they don't. The temporary cavitation threshold velocity in ballistic gelatin/living swine tissue can be calculated using MacPherson's equations. Duncan MacPherson is a literal rocket scientist, who did aerodynamics equations for the Mercury, Gemini, and Apollo rocket launches (IIRC), so I have very high confidence in his equations. Example velocity thresholds:

But rocket science is easy--you get to ignore friction in space, right: :) Actually, I do know of MacPherson's book, though I haven't read it; I put a reference to it in the ballistic gelatin article. scot 17:33, 16 December 2005 (UTC)

.177 caliber steel bb - 777 f/s

.177 caliber 7.9 grain pointed pellet - 1017 f/s

.177 caliber 7.9 grain wadcutter - 568 f/s

.45 caliber 230 grain roundnose bullet - 482 f/s

I haven't had time yet (finals week) to write Mr. MacPherson and ask if he minds terribly if I let people know the equations, or distribute my spreadsheet which calculates results based on his equations. He will probably say no, since the equations are one of the selling points for the book (at least they were to me). But I will say that the cavitation threshold velocity is based on two shape constants, bullet diameter, and the viscosity and density of the medium being hit. The above figures are for ballistic gelatin. Other media probably have different properties. Arrkhal 16:49, 16 December 2005 (UTC)

FWIW, I don't think you can copyright the data or equations, just the formatting; equations might be subject to patent however (since they aren't much different from algorithms, which are patentable). scot 17:33, 16 December 2005 (UTC)

Oh, I should probably add that penetration depth is not quite based on momentum/impulse divided by frontal area. This actually _is_ the case, between the penetration threshold velocity and the cavitation threshold velocity. But above the cavitation threshold, the equation is based on frontal area, mass, and a logarithmic equation involving the two threshold velocities and the striking velocity.

Energy only plays a role in penetration in either impacts between solids, or impacts between like materials (water hitting wate), I can't remember which right now. Flesh is somewhere between fluid and solid, and bullets are most definitely solid. Test data has shown that living tissue behaves more like a fluid than a solid, when penetrating ballistic projectiles are involved. Arrkhal 16:55, 16 December 2005 (UTC)

Energy in an inelastic collision goes into deformation of the substances. A steel ball hitting a steel ball, like those little pendulum toys, is an elastic collision and the energy is preserved. An airgun pellet into wax expends its energy cratering the wax--the more energy involved, the wider and deeper the crater. At high enough velocities, all impacts become inelastic--take a look at a high velocity impact, and even the hardest substances "splash" like liquids. With a velocity high enough, hardness (a constant) is so overwhelmed by the inertial forces involved (which increase with velocity), that a blob of mercury will penetrate better than a steel ball, because it has a much higer density (13.5 vs 7.5ish g/ml). The trick then is to get said blob of mercury accelerated up to several km/s, and holding its shape while it does so... scot 17:25, 16 December 2005 (UTC)

It would be really helpful if some pictures could be posted for the different bullets and their impacts. The lack of a visual aid really takes away from how informative this article is.

Would expanded bullets do? I can probably arrange some pictures of those in various calibers (though I don't have any expanded bullets, so I'd have to go shooting and trap some). I'd love some high speed photos of impacts, but I don't have the equipment to do that. With the right camera and flash, itt's not too hard. There are instructions on the web, if anyone want's to volunteer... scot 16:44, 15 January 2006 (UTC)

[edit] Momentum, momentum, momentum

Just ran across this article: http://www.handloads.com/articles/default.asp?id=6 which contains the following empirical observations:

The importance of bullet weight to penetration was demonstrated by John Linebaugh as a part of his Linebaugh Seminar held in Cody, Wyoming . In a nutshell, Linebaugh's results demonstrated once again that penetration of a non-expanding hard-cast bullet is a primarily a function of bullet momentum, which is the product of velocity times mass. In John Linebaugh's own words, "Velocity is constantly diminishing variable. Bullet weight is constant.", meaning for the hunter, penetration is a function of bullet weight first, and velocity second.

While it does not explicitly say so, one assumes that he is speaking with reguard to a given caliber--it is obvious that a larger bullet of the same mass and velocity would penetrate less, otherwise "non-expanding" would be irrelevant, and hollow points would be worthless. scot 03:57, 26 January 2006 (UTC)