If high speed bullets carry a destructive shock wave, why no paper target damage?


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The Real Hawkeye
October 10, 2005, 09:23 PM
We often hear of the destructive shock wave that travels with high speed bullets, but if this shock wave is so destructive to living tissue, why doesn't it cause paper targets to blow up?

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Amish_Bill
October 10, 2005, 09:46 PM
Ummm.... maybe 'cuz the paper of the target is only a zillionth of an inch thick?

Coltdriver
October 10, 2005, 09:47 PM
The "shock wave" effect you are referring to comes from the rapid displacement of tissue.

RyanM
October 10, 2005, 09:54 PM
The only real "shock wave" caused by a bullet impact doesn't do squat, anyway. A lithoriptor (kidney stone treatment thingie) generates shockwaves in your body upt 5 times as strong as those caused by a bullet, up to 2,000 times in one therapy session, with zero damage (except to the kidney stones).

There is some displacement of tissue due to the outward transfer of momentum, which can cause some tissue damage if it's displaced far enough. Partial fragmentation of the round helps, too. But it's not a "shock wave" anymore than a splash in water is a "shock wave."

If you want to see temporary cavitation work on paper (paper is inelastic, so it becomes a permanent cavity and you get a way bigger hole than with people), try shooting a phone book that's been soaked in water.

Majic
October 10, 2005, 10:16 PM
Paper has very little water content. The shock referral of a bullet is a function of hydraulics.

Lone_Gunman
October 10, 2005, 10:19 PM
The shock referral of a bullet is a function of hydraulics.

I don't think I have heard the term "shock referral". To what does that refer?

Gifted
October 11, 2005, 12:25 AM
So, what affect does a shockwave have on the ear? I've heard all that BS about shooting a .50 between two people, but it's gotta at least thump your eardrums if it's close enough.

Kurush
October 11, 2005, 02:55 AM
Supersonic bullets do make a shock wave--a sonic boom that is--but it isn't going to kill anyone just by passing near them. What kills people in explosions is heat and pressure waves, and bullets have very little heat in them, and they only displace the air that's immediately in front of them. So any pressure wave from a .50 BMG isn't going to kill anything bigger than a mosquito.

EDIT: I read some of the other responses, are we talking about shock waves in air or in the target? There are no shock waves in the target, Fackler said that tissue recoils (as a rule of thumb) at 1/5th the speed of the bullet which for any real world bullet is subsonic.

Also, water doesn't have shock waves at any speed, it's an incompressible fluid.

Medusa
October 11, 2005, 04:41 AM
There can be pressure waves in water, it is NEARLY incompressible. When you hit the water right above the fish with a paddle then the fish dies due the increased pressure at it's depth (of course, if it is shallow enough, say couple of yards). The pressure divides in liquid equally in all directions.

Kurush
October 11, 2005, 05:41 AM
There can be pressure waves in water, it is NEARLY incompressible.It's incompressible for all practical purposes. But you seem to have misunderstood me, I said shock waves are impossible in water, not pressure waves. A shock wave is a special kind of pressure wave that forms when an object passes through a compressible fluid at supersonic speeds.

If you've ever seen film of a bomb hitting the ground, that white film that spreads away from the blast for ~50 feet or so then disappears is a shock wave. Also when soldiers hear a "snap" (rather than a "whiz") from a bullet passing nearby their ears were inside its (relatively weak) shock wave.

Medusa
October 11, 2005, 05:45 AM
I know the difference between the 2, sorry about it, as am active in material sciences ;) But sometimes the difference between the 2 is quite vague.

EddieCoyle
October 11, 2005, 06:16 AM
We often hear of the destructive shock wave that travels with high speed bullets, but if this shock wave is so destructive to living tissue, why doesn't it cause paper targets to blow up?

Instead of a paper target, shoot a gallon jug full of water and you'll get an imperfect demonstration of what happens to living tissue (which is mostly water).

Medusa
October 11, 2005, 07:41 AM
http://www.aircraftresourcecenter.com/TPC/Funny_Pictures/0001-1000/0801-0900/0830/0830.jpg

The Real Hawkeye
October 11, 2005, 10:30 AM
I've shot lots of potatos with .22 caliber pellet rifles and have seen them splatter pretty good from a solid hit. Since these pellets do not exceed the speed of sound, I assume it is something other than a shock wave that causes this effect. Comments?

Justin
October 11, 2005, 02:12 PM
So, what affect does a shockwave have on the ear? I've heard all that BS about shooting a .50 between two people, but it's gotta at least thump your eardrums if it's close enough.

Supersonic bullets create enough sound to cause hearing loss. If you ever pull pits in a High Power match, they make you wear hearing protection.

A .223 zinging overhead sounds roughly about as loud as a .22 pistol being fired.

Kurush
October 11, 2005, 03:00 PM
I've shot lots of potatos with .22 caliber pellet rifles and have seen them splatter pretty good from a solid hit. Since these pellets do not exceed the speed of sound, I assume it is something other than a shock wave that causes this effect. Comments?The flesh of the potato resists the passage of the bullet much more than air does, which slows the bullet down. Since momentum is conserved (Newton's laws...), the potato recoils in the opposite direction of the force it was exerting. The momentum of the potato flesh is greater than the strength of the bonds holding the potato in its normal shape, so the potato flies apart.

I know the difference between the 2, sorry about it, as am active in material sciences But sometimes the difference between the 2 is quite vague.Cool. I'm a math student and I've worked on several research grants doing nonlinear materials simulation. There is definitely a lot of confusion out there about shock waves vs. pressure waves.

I think there would be a lot less confusion about this sort of thing if more people understood pressure waves vs. shock waves. So here's my humble attempt:

Shock waves, in ballistics, are only going to occur in the air, so there is really no point in talking about them except in relation to ear protection.

A shock wave is what happens when a fluid is being pushed faster than it can get out of the way (it can normally only move at the mach 1 by definition). Since the fluid can't get out of the way, it compresses into a very thin, very hot super compressed membrane. This is the film around the bombs I mentioned before.

As I mentioned, water is incompressible so it can't have shock waves; if you try to pass through water at > mach 1, it will just become very stiff and the object will either bounce off or be smashed. Also, mach 1 in water is ~4500 fps so we normally don't have to worry about it.

Gel/meat is compressible, and it's sort-of fluid like but (1) its speed of sound is even higher than water and (2) any shock wave is going to exhaust itself almost instantly by heating and stretching the nearby gel/meat and dissipate. Also, as I mentioned before in real tests gel/meat recoils away from a bullet at 1/5th of the speed of the bullet, so unless this is 2050 and we're shooting portable railguns or something at 20000 fps it doesn't enter into it.

thorn726
October 11, 2005, 03:01 PM
I don't think I have heard the term "shock referral". To what does that refer?

i'll venture it's about the same as conduction- the wave needs something to travel thru

brickeyee
October 11, 2005, 04:30 PM
If you ever gat a chance to 'play' with real explosives you can generate shock waves in water, even in steel and concrete. They are typically accompanied by fracturing of the material. Sometimes in predictable ways, sometimes not.
In terms of terminal ballistic behavior both momentum and energy come into play in any materials reaction to impact. The material properties determine what will happen, and due to the forces involved many things do not respond in an obvious manner. Notice in the picture of the apple being struck that material is ejected backwards relative to the impact.

ZenMasterJG
October 11, 2005, 04:57 PM
I've shot lots of potatos with .22 caliber pellet rifles and have seen them splatter pretty good from a solid hit. Since these pellets do not exceed the speed of sound, I assume it is something other than a shock wave that causes this effect. Comments?

This is just an energy thing.
The kinetic energy of a projectile is equal to half the mass of the projectile times the square of its velocity. (KE=1/2m*v^2)
When the pellet hits the potato, most of this energy is lost. (The pellet may go straight through and keep going, in which case it retains some of its kinetic energy.) Energy is conserved, that is, it doesnt just disappear. When the pellet puts its energy into the potato, its is dispersed as a little bit of heat, and a bunch of potato explode-y.

And yes, "Potato explode-y" is a scientific term.

Edit: sorry Kurush! Didn't see your explaination, which is better and more accurate then mine. The only problem with yours is you failed to use the phrase "Potato explode-y"

Kurush
October 11, 2005, 06:03 PM
If you ever gat a chance to 'play' with real explosives you can generate shock waves in water, even in steel and concrete.You can generate very strong pressure waves, you can't generate any shock waves.

Here's a table I got off the web:
temp F(C) 0 atm 500 a 1000 a 2000 a 3000 a
68 (20) 1.0016 0.9804 0.9619 0.9312 0.9065 So at 500 atm, (7,348 psi) water compresses about 2%
At 3000 atm, (44,088 psi) water compresses only 10%

In a shock wave, density inside the wave is typically triple the normal density. How much pressure would have to be applied to cause water to compress by 66%? (we'll be generous and ignore the change in temperature, which makes water even harder to compress)

Using least squares, we get a function approximating the pressure data above:
0.99713 - 0.0000314*xSolving that for .33 we get about 21000 atm (a whopping 308,614 pounds per square inch)

A direct hit from a nuclear bomb only creates about 5000 psi of pressure.

So I think it's safe to say that high explosives do not cause shock waves in water, they cause pressure waves.

silverlance
October 11, 2005, 09:44 PM
i've heard of horrible stories of idiots firing their glocks underwater and the pressure waves really f**** up their internal organs as a result.

this last one i heard of was some guy jumping into the deep end of his swimming pool and firing it at 10ft like a chlorinated navy seal...

RyanM
October 11, 2005, 10:27 PM
Those "firing a gun underwater overpressure" stories are complete, utter, 100% bunk. Ask any diver who's used a "bangstick" what it's like. Muffled thump, dead fish. Even in a small cave, just a muffled thump.

They can stun or kill a small fish if fired against a cave wall about a foot away from the fish, though. Mostly because the wall then projects the pressure wave straight backwards, towards the shooter, so it hits the fish at slightly reduced strength. And it still just sounds like a thump.

It's like trying to claim that the cylinder gap blast from a revolver will split someone's head in half if they stand too close to you at the firing line. The blast is definitely capable of taking a finger off if it's right up against the cylinder, but the danger level drops off pretty quickly with distance...

chris in va
October 12, 2005, 02:54 AM
All the scientists came out for this one. :rolleyes:

Medusa
October 12, 2005, 04:46 AM
Whaddaya expect from such a headline? :neener:

c_yeager
October 12, 2005, 05:00 AM
"Destructive Shockwave" :scrutiny:

mbs357
October 12, 2005, 08:05 AM
So how loud is the bullet's sonic boom?
That is, what noise would a gun/bullet make if there was absolutely no report--just the bullet's boom?

brickeyee
October 12, 2005, 12:07 PM
"density inside the wave is typically triple the normal density"

Not the correct definition of a shock wave. A shock wave is when the particel velocity exceeds the speed of sound in the media is a more workable definition, but still not entirely correct. See below.

"A direct hit from a nuclear bomb only creates about 5000 psi of pressure.

So I think it's safe to say that high explosives do not cause shock waves in water, they cause pressure waves."

I would suggest you review "Explosives Engineering" by Cooper.
Sound velocity is constant in the elastic region of a material. Up to the elastic limit you have a pressure wave. When the elastic limit is exceeded the wave front starts to speed up (is no longer proportional to change in pressure) and the pressure wave becomes essentially a vertical front. This is the transition to a shock wave. A wave is said to ‘shock up’ since the speed now increases with increasing pressure. A plot in the Hugoniot plane shows the pressure and velocity required to move into shock wave behavior.
See Cooper Fig 18.4.
TNT can produce pressures of 5800 PSI (40 MPa).
Cyclotol 8700 PSI (60 MPa).
Even more powerful explosives are available.

Kurush
October 12, 2005, 12:43 PM
Not the correct definition of a shock wave. A shock wave is when the particel velocity exceeds the speed of sound in the media is a more workable definition, but still not entirely correct. See below.I wasn't giving a definition there, I had defined it earlier. Your definition is just an atomic description of the definition I gave earlier.

What I was saying above is that you must actually compress the medium in order to have a shock wave, so I made a "napkin" calculation of the pressure necessary to effect sufficient compression of water.

When the elastic limit is exceeded the wave front starts to speed up (is no longer proportional to change in pressure) and the pressure wave becomes essentially a vertical front.You have just given a correct description of the formation of a shock wave in solid material. In a solid, the transition to shock occurs when the elastic limit is exceeded, in a liquid it occurs when the compression is sufficient to cause a phase change.

Obviously, fluids have no tensile strength and therefore no elastic limit so the definition for solids can't even be applied to water. If you want to expand on my "napkin" calculation be my guest, I freely admit it is not fully correct, but I do believe it is a valid lower bound.

mbs357
October 12, 2005, 12:46 PM
So, particles moving past the speed of sound = shock wave? Particles as in dust particles/molecules/etc? What do you mean by particles?

And when people usually refer to a shock wave, like an explosion's shock wave, they're actually talking about a pressure wave?

Too Many Choices!?
October 12, 2005, 01:07 PM
We just need,"Too Many Choices!?", and a few words: Here we go,AHEM, Paper ain't people, therefore it doesn't compress, therefore it does not create a preassure wave.The papers rigidity(or elasticity depending on material) is overcome before the paper cab can compress to give the explosive effect of the preassure wave release upon exit. No Compression, no explosive wave. Add more paper, and wet it like another poster said. .40 Cal hollow points out of a, Glock 23, do a number on a phonebook, but don't penetrate, and leave one hell of a mess of the paper intwined(literally welded together) with the expanded bullet;"Shrapnel". I don't want to think about it mangling flesh that way:eek:

Daniel T
October 12, 2005, 01:17 PM
All the scientists came out for this one. :rolleyes:

What's your point? Would you rather end the discussion at "BULLET GOES BANG!"?

If it's over your head, pass it by.

bad LT
October 12, 2005, 01:30 PM
Agggh - You guys are reminding me of my fluid mechanics tests.

The Horror, the horror

Justin
October 12, 2005, 01:44 PM
So how loud is the bullet's sonic boom?
That is, what noise would a gun/bullet make if there was absolutely no report--just the bullet's boom?

Again, my experience with pulling targets in the pits at a High Power rifle match.
You hear the bullet fly overhead, which, with hearing protection in, sounded roughly equivalent to the report of a .22 pistol.

Then shortly after you hear the report of the gun itself.

So the whole thing sounds like a sharp *crack* overhead followed by a distant *boom.*

Kurush
October 12, 2005, 04:05 PM
So, particles moving past the speed of sound = shock wave? Particles as in dust particles/molecules/etc? What do you mean by particles?In air and water we are talking about molecules.

And when people usually refer to a shock wave, like an explosion's shock wave, they're actually talking about a pressure wave?In my experience most people will refer to overpressure as a "shock wave", yeah. However HEs do cause shock waves in air and in critters, out to a certain range.

If someone says: "wow, look at the shock wave of that bomb" referring to the visible shock front, he is using it correctly.

If someone says: "we dropped a depth charge, and the shock wave made a huge water spout" they mean "pressure wave".

If someone says: "The deer I shot had bruising from the big shock wave that went through it" he means "pressure wave".

Finally, if someone says: "I shot a deer with my Hydro-shoks in the ankle and the 'hydrostatic shock' sucked its brains out!" they are full of baloney :p

So how loud is the bullet's sonic boom?Not very loud, the bullet doesn't displace much air so the amplitude of the shock wave is pretty weak. Most of the noise from a gunshot comes from air being displaced by the expanding gasses produced by the gunpowder. I'm not volunteering to have a .50 shot right past my ear mind you but I don't think it would break your eardrum.

brickeyee
October 12, 2005, 06:46 PM
"...in a liquid it occurs when the compression is sufficient to cause a phase change."

The 'elastic limit' in water is normally taken as cavitation.
No problem. How big a bubble do you want?

Cosmoline
October 12, 2005, 06:51 PM
What I have read in many sources is that once bullets get beyond about 2,200 fps they start to have an "explosive" impact on flesh from their speed alone. However I have never seen a really scientific test of this. Ballistic gel isn't going to work, unless it can replicate the myriad of tiny capilaries and connective tissue that is supposed to bear the brunt of the shockwave.

RyanM
October 12, 2005, 07:37 PM
What I have read in many sources is that once bullets get beyond about 2,200 fps they start to have an "explosive" impact on flesh from their speed alone.

Partially true. Somewhere in the 2,000 to 2,500 fps range is a threshold at which standard construction softpoints start to fragment. The combination of fragmentation and relatively large temporary cavity have a synergistic effect; the fragments make multiple small holes, then the temporary cavity is able to tear the tissue much more easily.

For instance, if you compare this picture (http://www.firearmstactical.com/images/Wound%20Profiles/M80.jpg) with this one (http://www.firearmstactical.com/images/Wound%20Profiles/308%20Winchester.jpg), you can see that the maximum diameter of the temporary cavities is about the same (a bit under 8" for the FMJ, around 9" for the softpoint), but the fragmenting bullet makes a much larger permanent cavity. You can also see that while this (http://www.firearmstactical.com/images/Wound%20Profiles/30-30%20Winchester.jpg) .30-30 at 2017 fps created quite a large temporary cavity (a little more than 6") and did fragment a bit, there just weren't enough fragments to cause an "explosive" effect like the .308.

Testing in actual living tissue has borne this difference out. Click here (http://www.btammolabs.com/articles.htm), and download the article entitled "Bullet Fragmentation: A Major Cause of Tissue Disruption" (third one down). On the third page, you can see photos of cross-sections of thigh tissue of a piggie. It may be a bit hard to tell, but that tiny little white spot in each of the three top pieces of meat is all the bullet hole you get with nonfragmenting, non-expanding ammo.

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