What is "Knock Down Power"

P

plinky

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I've recently been looking at Youtube vids about knock down power of a handgun caliber.

The most popular debate being the 9mm vs the 45acp.

None of it is making any sense to me.

Not long ago I read a hunting article that went over a similar topic, that being what caliber knocks game off their feet. The author went on to say basically none of them do. An animal may fall instantly if the proper internals were hit. Altough I do imagine a .50 would knock a squirrel off its feet, but that's not a real application scenario.

Back to the 9 vs 45 debate, I seem to remember seeing that there's only a 15% difference in kinetic energy between the two. And I'm not sure what kinetic energy is in relation to knock down effect.

And if a bullet could knock a person down wouldn't it also knock the shooter down? Something about an equal and opposite reaction type of thing going on there.

Any sensible explanation would be greatly appreciated.

Kind Regards, Jim
 
What knock-down power is, is a myth. Especially for handgun calibers.


There may, MAY, be a phenomenon of measurable effect, called "Hydro-static Shock" wherein the impact of a bullet causes shock and disruption to the nervous system and causes immediate (but temporary) loss of control and/or collapse. If this effect exists, it requires impact speeds well beyond anything found in normal, or "typical", handgun cartridges. The number is typically put at a minimum speed of 1800fps.
 
What knock-down power is, is a myth. Especially for handgun calibers.
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I agree. I'll even take it a step further and say that it doesn't exist for most rifles either. Not that a .308 won't knock a deer down, but that doesn't mean that it will knock a deer down either.

There are different ways to measure the energy of a fired bullet but none of them can actually translate into a means that can measure or calculate the "knock down" of the target.

If someone claims that they can measure knock down power, I'd suggest they don't really know what they are talking about.
 
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It's also referred to as "kinetic energy". Some bullets can and will knock and animal/human of its feet.

Regarding an equal/opposite reaction, you have a supersonic projectile slamming into soft-tissue, bone and cartilage. That is where you get your equal/opposite reaction from; not the gun.

An effective hunting round/SD round will have hydrostatic shock along with CNS/Cardio-Pulmonary damage that aids in "stopping power". If you shoot a major artery, you'll bleed out in 15 seconds. If you shoot a nerve, muscles will either go limp, or stiff and lockup-as well as other functions of the body (breathing, cardiac conductivity, vaso-constriction, shock response)
 
Just as peetzakilla said---it's "urban legend". Bullet impact delivers the same amount of energy at both ends of the shot--rapid acceleration and rapid deceleration--the only difference is how that energy is absorbed by the target vs. the recoil felt upon firing. What might be perceived as "knock-down" power is in individual bullet performances in different mediums (penetration, expansion, permanent and temporary wound cavity, etc.

Some bullets can and will knock and animal/human of its feet.
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Wrong. The body's reaction to the bullet impact might cause a "jump", but it's not the bullet knocking anything down.
 
Another +1. A term that simply needs to die.


The body's reaction to the bullet impact might cause a "jump", but it's not the bullet knocking anything down.
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Its the "oh crap, I'm shot" effect.
 
thesheepdog said:
Some bullets can and will knock and animal/human of its feet.
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This is not true at all.

Do the math. The maximum energy transfer from a VERY powerful rifle cartridge will cause less than 1 mph motion in a 150 pound person. At the very most, THE ABSOLUTE VERY MOST, this might cause a person to take a step back to regain balance. AT THE VERY MOST.

Even that effect would require a point blank shot from a very hot and heavy 50 BMG.
 
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What Causes This?

If someone is sitting in a chair and you stick them in the rear with a very low velocity and low weight pin they will jump up. I can find no term for this.
 
When I was 15 or so, a friend shot me with an arrow that the tip had been knocked off of. Maybe a 50 lb pull bow and we were f'ing around shooting some little bow at targets. I turned my back to get something and ZOCK right below the shoulder blade from about 15 feet away

Yes I kicked his butt later

Didn't stick in me but I'll tell you it hurt. Thought I had a broken rib.

It "knocked me down", but it was the surprise and pain that turned me into a pile of jelly
 
I can find no term for this.
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It's called fight or flight response. It's basically just an adrenaline rush to pain, stress or any intense nervous response.

Have you ever immersed yourself in freezing cold water and your body has the response of inhaling and your muscles tensing up? That's fight or flight.

Andrenaline (technical term is epinephrine) shuts down peripheral nervous responses to pain, temporarily; like when you injure yourself badly, at first, you're in shock, then the pain creeps in and you begin to faint. Fainting is an adrenaline response as well (2nd stage I believe).

Does this some it up?

Peetzakilla,

That's what I am saying. It's not ALL the bullet, it's mostly the response from your body. But SOME bullets will not cause that fight or flight effect.
 
Energy does not equal momentum. Momentum is what would cause a person to fly of their feet. A bullet just doesn't have enough momentum to do this. They're all too small. Run the numbers.
 
Here's the math....


The impulse imparted by a 2895fps, 800gr 50 BMG bullet would be:

45.742639190617 kilogram-meter/second


That impulse, applied to a 150lb man would yield a velocity of:


0.67230171428504 meter/second


That's a speed of 1.5038961 miles / hour, or roughly half of normal human walking speed.

In other words, one step would restore balance.
 
Peetzakilla,

The math is there, but think realisticly here; you have to factor deceleration as well; because once a bullet expands, you're creating surface area, and surface area will create drag.
How does this apply if your bone gets shot? Think of shooting a 2X4 with a hollow point. I am sure you have done this, and i am sure you can disagree that it's moving at 1MPH-given a 2X4 isn't 150lbs.
 
No such thing. What can be considered is the momentum of the bullet which is the velocity times the weight of said bullet.
 
Mythbusters actually did some work on this in one episode in a segment called "Blown Away". They tried firing a number of firearms into Buster at close range, and even a shotgun at close range was only able to make him "drop" from the stand.
 
Yeah it's a myth. Never heard of a person being knocked off of their feet from being hit by a round from any handgun.

I believe in takedown power. But my theory is not on the power of a round but based on talks with military snipers. It goes like this. "You hit vitals and they'll drop." Now with a handgun I can see taking more than one shot. Rifles are different. A lot more room for delivering the right round with the right amount of energy to the right area of the target. Just the way it is. And before you debate. I said drop, not "knocked down" or "blown away". Truth is even with one shot on vitals from a rifle, targets tend to drop like a rag doll unless the nervous system goes into panic and the corpse starts jerking around as an after effect, then it's just a drop and a bunch of jerking around. As one sniper said "The body doesn't know that it's dead yet."
 
It was very popular, at one time, to try to predict or quantify "stopping power"; TKO, Relative Incapacitation Index, Relative Stopping Power, etc. Most of the old ones were variations on measurements of momentum. While there may be no such thing as "knock-down" power in a shoulder-fired or hand-held weapon, I might be more interested in the opinions of what worked, among those who actually shot lots of things in the field or in combat, than those who do most of their "shooting" in a lab or at a computer. That is, I've found that most published writings on terminal ballistics among the old-timers was done from experience killing things, while a lot of what I read today is predictions based on models and statistics.
 
What knock-down power is, is a myth. Especially for handgun calibers.
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That's like saying that the energy of the bullet doesn't matter, so, therefore, more powerful handguns are of no value.

If the energy is properly harnessed, then it does matter.

A bullet's ability to do more damage based on it's higher power factor is dependent on bullet design to take advantage of it, especially where rifle bullets for dangerous game are concerned.

But also for pistol ammo where the extra power can be used to expand a bullet more, quicker, and drive it deeper. Otherwise, the extra power is wasted--as with inferior bullet designs.

As for those who disagree with the effective of the temp. cavity playing a part in incapacitation, I don't necessarily agree. The .357 Mag. wasn't head and shoulders above most other calibers (that penetrated and expanded the same) just by magic. Velocity likely had something to do with it.

While "knock down power" isn't a very sophisticated way to describe it, at least we know what it refers to.:cool:
 
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