Wait a second, 'knock down power' ???

[artherd]

OK, I've been wondering how the idea of 'knock down power' came into the popular venacular?

Basic physics tells us that all the energy in a bullet's acceleration in a barrel must be exerted equally on the gun (and thus the shooter.) There is then also the additional reactive force of the ejecting gases (acting like a rocket engine) that occur after the bullet has left the barrel and on it's merry way.

So, any 'knock down power' any particuliar human-mount-fired projectile posseseses must be visited upon the shooter at least equally, if not in greater magnitude.

Infact, it is only the added mass of the gun (which just lowers the velocity of the impulse, and somewhat in concert with the stock, legenthens the interval in which it is presented as a force.) and the wider area of the butt-stock that prevents a gun from being driven into the shooter's shoulder.



So how can a round be said to have much of a 'knock down power' type effect? (incapacatative effects, which with CNS hits can be devistating, notwithstanding.)

[armoredman]

I believe that is a refeence to the old Taylor formula, that when carried to an extreme, said a slow moving bowling ball had outstanding knock down power. Correct me if I am wrong....

[TonyB]

Hard to conceal a bowling ball though.....not to mention follow up shots:D

[WonderNine]

Something that will fire a bullet that does not hit a CNS area through an attacker fast enough to cause them to collapse from shock. I'm not aware of any handguns that can do this. Rifles however do.

[clubsoda22]

It's all mindset, some people will get shot and fall down from mental shock. Others will take another hit of PCP, rip off a car door, take a bite out of it, and mot think twice about the bullet in them.

[Sean Smith]

Artherd,

If you are going to cite "physics," maybe you should understand it. ;)

For instance, the recoil energy felt by the shooter is dramatically less than the kinetic energy of the projectile. The conservation of energy only tells us that the total of the potential and kinetic energy has to remain constant. Thanks to, among other things, the inertia of the firearm, the gun doesn't hit you as hard as the bullet hits the target. Using a recoil calculator, you may find that a projectile with 400 ft-lbs of kinetic energy and traveling 1,200 ft/sec at the muzzle may only generate 5 ft-lbs of recoil energy at 11 ft/sec, depending on the mass of the gun firing it & other factors. Furthermore, recoil forces are spread out over a greater surface area & time than the impact forces of the bullet hitting the target, which definitely makes the target more apt to be "knocked down" than the shooter.

Note that this doesn't "violate" any laws of physics, e.g. conservation of momentum or Newton's 3rd law. Also, in a gravityless vacuum almost any force would be able to knock down a shooter or shootee... thanks to things like gravity, air resistance and friction that isn't the case. You just have to take everything into account, at which point it becomes clear that a gun definitely does not hit you as hard as its bullet hits the target (and is thus much more apt to make a target fall down than the shooter).

So to answer the question, yes, you could concievably make a weapon that knocks a target down without knocking you down. But as a practical matter, none of the handgun calibers out there (at least this side of .500 S&W Magnum) are able to actually do it.

[critter]

Sorry Sean. Momentum IS conserved in particle interactions: gun-bullet-firer vs bullet-recipient.

However, kinetic energy IS NOT necessarily conserved in interactions (for example-knockdown). It is used up in friction (barrel, air) AND in cutting, ripping, tearing, splattering, poking holes, etc. and not necessarily 'knock down'.

Kinetic energy is conserved in PERFECTLY ELASTIC collisions (sort of like the collision of 2 superballs in an atmosphere and friction free space).

[cordex]

Anyone seen the video of Richard Davis taking a .308 to the chest while standing on one leg? (While wearing a bullet resistant vest, of course.)

The force is not there to club a person to the ground unless they are already off-balance and ready to go down.

[armoredman]

Yes, and it was the other guy, not Rich in the movie Deadly weapons, who did that. Rich did the shooting, and the other guy was wearing a level five raid vest. All he did was sway back and forth. BUT, to address the other post, the vest spread the force of the weapon across a large area, a force dispersal mechanism, as a bullet concentrates force in a very small location.

[cordex]

Whoops! My bad. The other fellow, then.

[krept]

as mentioned, could be part psychological as well.

take a 4" needle for example. if it takes .1 second for the entire needle to be stuck into your chest, you will be standing and thinking 'ouch.' OTOH if it takes two seconds for the needle to go in, chances are you will try your best to go in the direction that the needle is moving in to alleviate the pain.

So, with this sorry analogy, maybe a slower bullet imparts more of the feeling of 'I should be moving away from this energy' thus adding to the perceived knockdown. :scrutiny:

[TheEgg]

My Louisville Slugger has "knock-down" power, not my handguns.:neener:

[Black Snowman]

From my hunting experiance nothing is "knocked down" by a bullet. The trauma it induces causes the "knock down". To address the original question I have no idea how this horribly inaccurate description came about but I can put forth a good guess.

I think it's most likely from the early days of the English language and quantified physics where to a casual observer things appeared to be "knocked down" by a bullet. The phrase was most likely coined before Newtonian physics were common knowlege.

[Sean Smith]

Sorry Sean. Momentum IS conserved in particle interactions: gun-bullet-firer vs bullet-recipient.

I never said momentum WASN'T conserved. I said that what I described (the kinetic energy of bullet at muzzle not equal to the recoil energy) didn't violate conservation of momentum (i.e. because momentum is conserved).

Read closer. ;)

[Quartus]

So how can a round be said to have much of a 'knock down power' type effect?


Ignorance.

[WonderNine]

It's all mindset, some people will get shot and fall down from mental shock. Others will take another hit of PCP, rip off a car door, take a bite out of it, and mot think twice about the bullet in them.

I understand what you're saying and I agree, but I think it's been demonstated that rifles with do this, while handguns are not capable of causing such a "shock" effect on a person because the bullets move too slowly.

Following the other theme regarding pistol caliber knockdown, I suppose it would be logical to say that a .45 is more "efficient" in transfering its energy to the target than a smaller caliber round because of its larger diameter bullet, but of course it would still be unable to knock somebody down to begin with just by the insignificant amount of force it distributes on the target in the first place. Imagine the small amount of recoil distributed from a two pound gun on your hand. Sure the gun by itself would get knocked down from the recoil, but a 150-250lb. person getting knocked down from a bullet that already has lost some of its energy?

[cidirkona]

Go rabbit hunting with a 30-06... now THATs knock-down-power. The total energy exerted pushing on the entire palm of your hand is greater than (due to air resistance) - although it's also doing the accelleration across 3-5 inches as well. You can get in a car going 65 and slowly come to a stop with the brakes or you can run into a wall - either way the same amount of energy is absorbed - but when it happens quicker and in a smaller area it's more 'concentrated' - I think...

This also makes me wonder about "penetration" in gelatin testing. People always seem to want deep penetration - but wouldn't you transfer more energy into the subject if it slowed down quicker, or completely? A 95 grain bullet that goes in a 1000f/s and comes out at 500f/s doesn't transfer as much energy as one that goes in a 1000f/s and doesn't come out... right?

E = m*v^2 Energy = mass times velocity squared.

Then again... energy transfer doens't mean the same thing as damage done. A car hitting a wall and a car using it's brakes absorbs the same amount of energy.

-Colin

[horge]

Hmmm...

All other things being equal, a bullet that penetrates deeper affects a larger percentage of the target's total volume, especially if you consider the velocity required and the concommitant temporary wound cavity.

Obviously, if you want to get past ribs and like obstructions in order to get to organs of stoppage consequence, you want good penetration through an arguably more-forgiving medium like 10% ballistic agar --I'd think something on the order of 12-16". With a bullet, all other things being equal, penetration is dictated by velocity... but I'm not about to endorse any silliness based on shooting fictitious goats, or badly-flawed statistical analysis of 'street' incidents.

Fackler's better-informed camp doesn't like studies that dwell solely on temporary wound cavities, but in terms of psychological effects, a larger percentage of the target's volume being disturbed ought to get the target's attenion.

All things NOT being equal, then the obvious trade-off between penetration vs. wound diameter (velocity, bullet weight and shape, ad nauseam) comes into play, no?

A CNS hit is often a tough proposition, as the head is a small target and the spinal cord is way in the back of all that obstructing tissue and bone. I'll take a CNS hit if I can get it, but it's perhaps better to count on psychological shock and rapid, massive blood loss to neutralize an attacker.

Both require sufficient penetration and a respectable temporary and permanent wound diameter.



Knock down power?
If I want to see real knock-down power,
I'll go watch Manny Pacquiao in the ring.

:D

[Dr.Rob]

"Knock down power"

A phrase in use in handgun marketing since the turn of the last century.

[goon]

I sort of think that the knockdown power thing is overplayed.
I have shot steel plate targets with 7.62x54 quite a bit and there is no dramatic flying of the target.
They weigh anywhere from 25 to about 40 pounds and they just fall over or maybe move a couple feet when they are hit.
Even with a dead solid center hit they are only pushed a couple feet away.
My conclusion is that the knockdown thing is just another thing for us to argue about.
A hole in your chest is a hole in your chest.
A bigger bullet does more damage, that much is true.
But a hole through something vital is still a place where stuff will leak out.
Best way to stop someone is a CNS shot, and if you make that shot any sufficient caliber will do.
If no CNS you just keep shooting till the lead weighs them down.
Just my .02.

[Frohickey]

The other thing is that after so many Hollywood movies of loud noises, and people falling down, the mind has been conditioned that this is the way a body has to behave.

[Dave Markowitz]

If you want knock down power, use a Buick.

[armoredman]

Peterbilt.

[MrAcheson]

I never said momentum WASN'T conserved. I said that what I described (the kinetic energy of bullet at muzzle not equal to the recoil energy) didn't violate conservation of momentum (i.e. because momentum is conserved).

Sorry Sean, but your analysis is still fundamentally flawed. We are talking about people being thrown about by bullet impact. An energy analysis here is practically meaningless. Yes the chemical potential energy of the bullet becomes gun kinetic energy and bullet kinetic energy. It also becomes heat and sound and other things. Doesn't matter because you can't use it to calculate anything else. Nor does a small "recoil energy" on the part of the firearm given any indication of its felt recoil. These are classic momentum problems where energy is totally inappropriate.

Artherd, rounds can knock people down because of injury or percieved injury. More than once I have rolled with a minor impact all the way to the ground. Its not because I couldn't stood and taken it, its because I would have gotten hurt doing so. I have gotten an electric shock that knocked me across a room. Except that it didn't, my reaction to the shock did. A lot of "knock downs" are like probably like that they put the person off balance, hit a nerve, or simply triggered some part of their brain that says "people that are shot are supposed to fall down and die" so they do. Sounds stupid but it does.

[BluesBear]

I was an exibitor at the Muncie Indiana Gunshow in 1979.

A fellow standing directly in from of my table had a negligent discharge with a Colt Government Model .45.

The impact knocked me backwards about two feet where I fell into a chair ending up in a sitting position.







What was this powerful projectile?







The ejected cartridge case.

[Sean Smith]

Sorry Sean, but your analysis is still fundamentally flawed.

:rolleyes:

[jacketch]

"Thanks to, among other things, the inertia of the firearm, the gun doesn't hit you as hard as the bullet hits the target."

Does this mean a human body (much heavier than a pistol) doesn't exhibit inertia?

[Tactical]

It's all mindset, some people will get shot and fall down from mental shock. Others will take another hit of PCP, rip off a car door, take a bite out of it, and mot think twice about the bullet in them.

This is why you aim between the ears.

[MrAcheson]

Does this mean a human body (much heavier than a pistol) doesn't exhibit inertia?

It actually means the word "inertia" had no business being in that sentence. Sorry Sean, but your explanation is a true mishmash of physics jargon.

The bullet leaves the gun. Momentum conservation means that the gun moves backwards as the bullet moves forwards. However the gun is heavier so it moves slower. The gun now hits the shooter (their hand). Because the gun is moving relatively slowly, the shooter can absorb the recoil impulse safety over large time with small force. The shooter ends up moving even slower than the gun, so they probably won't get hurt.

The bullet hits the target. Lets assume the target wasn't moving and the bullet didn't slow down any. The bullet slows down very fast in the target . This requires a lot of force so the target is going to get hurt. However if the target is the same weight as the shooter, they end up moving the same speed in the opposite direction.

The trick is that the gun lets the shooter absorb the recoil safely which the target doesn't have that luxury so while both get pushed the same the target gets hurt and the shooter doesn't. The real reason the target falls down is that the target is injured and this can cause him/her/it to fall.

[Robert J McElwain]

This is an interesting thread.

Let me ask a practical question along the lines of "knock down" and inertia and all that stuff.

Let's assume two different people are hit by bullets and in both cases, only soft, non-fatal tissue is hit. One bullet is of moderate caliber from a hunting rifle with moli-coating and solid tip. Not any kind of hollow point.

The other person is hit with a .45 ACP hollow point.

What will be the different effects?

Bob

[bountyhunter]

That a 200 pound man can be "knocked down" quite easily by a force of a few pounds. It's called BALANCE.

I remember when teaching martial arts, the first thing we would do to a newbie is tell them to stand firm and not move. Then take one finger and push into their chest (center of mass) and they fall over with almost no effort. The point was that you can knock someone down easily if the impact is such that it breaks their balance. In karate, you consciously adjust knee flex and weight distribution to reduce the opponent's ability to break your balance. With a bullet, you can't because it's coming too fast.

We had a cop in San Jose knocked down by the "wimpy" 9mm when he was shot in the hip bone. The bullet stopped instantly so it delivered all of it's energy to his hip bone. The hit was off center and spun him around sending him to the ground. It was no a serious wound, but it definitely was a knockdown.

[FireInTheHole]

Armoredman:
I didnt know there was body armor available beyon level IV... how many rounds of .308 can a 'level five raid vest' take?

Question:
If one had body armor thick enough and sturdy enough withstand (without turning the said person's internals into puree) a center of mass shot from a .50BMG would that shooter get "knocked down"? (roughly 12,000 ft-lbs)

Or even more realistically, a 3" mag slug from a 12 gauge. Many body armors claim they can stop slug loads but would a 1oz slug going 1200fps knock down a person? (roughly 1400-1500ft-lbs)

[bountyhunter]

If one had body armor thick enough and sturdy enough withstand (without turning the said person's internals into puree) a center of mass shot from a .50BMG would that shooter get "knocked down"? (roughly 12,000 ft-lbs)

Yes, he'd get knocked down. he would also certainly have a ton of broken ribs and massive internal injuries from the shock wave that went through his body. he would also have severe burns as most of the energy of the bullet is transformed into heat as the armor stops it, and that heat is focused on a small area. Cops shot in vests usually get a bruise and a burn.

[Feanaro]

From what I know most "knockdowns" in a firefight, IE someone falling over, occure because the people in question have had a hole open up in their body. There is not enough energy in the bullet to knock the person down... but the large, thirteen inch hole that they are left with might do it.

Take a 7.62 NATO round and hit someone with it. The bullet does not have enough energy to knock that person over. But the internal injuries would probably do it. But take one of those 700 Nitro bullets, with 100+ pounds of recoil and it could knock someone over. After all, it almost knocks the shooter over. ;)

[jc2]

"Knock down power"

A phrase in use in handgun marketing since the turn of the last century.

Actually, it has largely been replaced "One Shot Stop (OSS)" since we now have a "Definitive Study :rolleyes: ."

[artherd]

I think it's safe to say that the shooter expierences approximately the same total impulse as that of the person being shot. The latter may expierence it in a shorter interval of time (decelration in 8" vs ~22" of a typical rifle barrel.)

If one were off balance, or otherwise not expecting it, the blunt force from either end of a high powered rifle could knock someone down I suppose.

It is actually much worse if you are wearing a vest, because the bullet will be stoped in less than 2". That's a lot of force per unit time.

Best!
Ben.

[MrAcheson]

It is actually much worse if you are wearing a vest, because the bullet will be stoped in less than 2". That's a lot of force per unit time.

Not necessarily, the vest has weight so, like the gun on the other end of the problem, it can help reduce felt impact. The bullet hits the vest which hits you. Also a good vest will spread the impact over a larger area so it won't hurt as much.

he would also certainly have a ton of broken ribs and massive internal injuries from the shock wave that went through his body.

Sorry but the great thing about body armor is that flesh is much softer than body armor. Why is this great? As the shockwave propogates through the armor and hits the armor/flesh inferface, the softer flesh will reflect most of the shockwave back through the armor towards the bullet. Its really neat. This is why some more advanced vehicular armors have thin layers of rubber in them. The shockwave hits the rubber and gets reflected back towards the incoming bullet.

[corncob]

what kind of education/background/practical experience do you have with physics? You sound like an old, classically-trained engineering professor. (I'm in my junior year of engineering school.)

[JShirley]

artherd,
As Dr. Rob said, marketing hype. Saw another old add recently that talked about a rounds' "smashing power" or something like that.

Or even more realistically, a 3" mag slug from a 12 gauge. Many body armors claim they can stop slug loads but would a 1oz slug going 1200fps knock down a person? (roughly 1400-1500ft-lbs)

Well, I can tell you from personal and recent experience that exact load (Remington Reduced Recoil 1 oz slug) may not knock down a big deer weighing about what the average man weighs.

It will plow through him, though! Add several hundred FPS for a 3" magnum slug. Remington's 3" magnum (http://www.remington.com/ammo/shotshell/slugger.htm) load is a 1 oz at 1760 fps, giving just over 3000 ft-lbs of energy at the muzzle!

[444]

"This also makes me wonder about "penetration" in gelatin testing. People always seem to want deep penetration - but wouldn't you transfer more energy into the subject if it slowed down quicker, or completely? A 95 grain bullet that goes in a 1000f/s and comes out at 500f/s doesn't transfer as much energy as one that goes in a 1000f/s and doesn't come out... right?"

That may all be true, however, as has been mentioned a number of times in this thread, it seems that knock-down is a myth, so energy transfer doesn't mean a whole lot: especially when we are talking about handgun ammo. So, we resort to plan B: putting holes in vital organs to promote rapid and severe bleeding along with allowing air into the thoracic cavity which will eventually result in a tension pneumothorax and or hemothorax. This is where penetration comes in.
You can hit someone with a baseball bat in the chest and all the energy is disapated. And some serious energy is involved. But, in all likelyhood it isn't going to kill the person. But, putting a hole completely through the chest will, most likely kill them.
I never took physics. I however do know a few things about gunshot wounds. Air in, blood out = good. Two holes are better than one for a couple reasons. Boring a hole clean through the middle of someone's chest is the most reliable method of stopping them with common, handheld weapons.

[BluesBear]

Boring a hole clean through the middle of someone's chest is the most reliable method of stopping them with common, handheld weapons. Since the best way of ensuring a "clean through" path would be to use full metal jacketed bullets, you are saying that FMJ would be the best for personal defense?

[444]

Compared to what ?

Two holes are better than one.
If you can get the holes bigger, the bigger the better.

Personally, if I had the choice between having two holes and having expansion, I will take the two holes. If there is a way to get both, I will take both. One obvious way to do that is to use a larger caliber from the get go: I took advantage of that from the beginning.

In the example mentioned, we have two 95 grain bullets traveling at 1000 fps. One completely penetrates and leaves at the speed of 500 fps. The other bullet stays within the body. There really isn't enough information to make any real judgement, but it sounds to me like the first bullet would be the better one.
First of all, there is not enough "energy" involved to make it a factor. We don't know if the first bullet disapated all it's energy on something like the sternum and never reached any vital organs. We don't know if the bullet penetrated two inches and petered out. We don't know if the bullet completely fragmented on impact and only did minor flesh damage.
The second bullet gave us complete penetration. That means there are two holes and everything in between those two holes has a hole in it. Everything between those two holes is bleeding.
Expansion is nice. Penetration is essential. Both is better, but if you have to make a choice, penetration is essential, expansion is icing on the cake. It doesn't matter (within reason) how much the bullet expands if it doesn't reach the vitals and put a hole in them.
There is no rocket science here. There are no magical properties involved. People dying from penetrating trauma is nothing new. The way a hangun bullet kills and the way a spear, or knife, or sword kill is the same as it has been since the dawn of time. You have to put a hole through the vital organs. You want bleeding. More bleeding is better. You want air to enter the chest cavity. More air is better.

[M58]

Closest I have seen is the 12ga. bean bag from our riot guns.
But it is not true knock down.
It is shock and pain.