Help with an Argument on "knock down" power

[Tennessee Gentleman]

Brothers and Sisters,
An old Army buddy and I are arguing about the phenomenon called knock down power and I have stated that it is a myth.

Further, I have stated that Newton's Third Law renders the idea impossible in that a round fired with enough "power" to knock down a person (standing normally and not drunk or drugged) would also knock down the shooter.

He says "Ahh, Newton’s third law…it doesn’t apply as you imply. If the bullet stopped at the muzzle with no means of continuing forward or projecting that force forward, the reciprocal force might cause the shooter to be knocked down. But, since the forward force is continuous and dissipated along the trajectory of flight (and the backward force is mitigated by recoil controlling design) said knocking down of the shooter only happens occasionally."

He is a .45 ACP guy.

So, what am I missing?

[David R]

My father told me if I got hit in the hand with a 45, with my arm extended, it would spin me around.

I am now 57 and do not believe that.

David

[TunnelRat]

He’s wrong and he even helped your argument. The force felt by the shooter isn’t a function of the total flight of the bullet. It’s a function of the duration of the time that the bullet is able to act upon the pistol itself. This is completed by the time the bullet leaves the barrel. Moreso pointing out how the bullet is slowing down during its flight reinforces the point that when the bullet strikes its target it does so with less force than it was able to impart to you as the shooter. Meaning if firing the bullet isn’t capable of knocking down the shooter then it surely isn’t capable of knocking down the target just by itself as it has less force to do so. As for the mitigating force of a recoil spring, recoil springs are typically rated at say 20 lbs and less. Compare that to the weight of a human being. The amount of force the recoil spring can handle is a small fraction of the weight of a person. Meaning if the force was truly enough to knock over a person the recoil spring would be destroyed in a single use and it’s highly unlikely it would be able to take off enough force to stop you from being knocked over.

People don’t get knocked down by bullets. They fall down from trauma. As for “knockdown power”, if you look up on YouTube there used to be a gentlemen that demonstrated his Kevlar vests by shooting himself in the chest at point blank range with a 44 magnum. He doesn’t move. If 44 magnum isn’t “knocking down” someone, 45 ACP sure isn’t.


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[UncleEd]

Tennessee Gentleman,

You take a Colt's 1911 .45, perhaps your friend's, and
whack him across the top of his head. You'll knock
him down.

Then apologize that you were wrong.

[Sharkbite]

Have him shoot a hanging heavy bag (75-100lbs). Watch how much it moves (not much) and ask him how that amount of movement (or lack of), would “knock em down”?

I can move a heavy bag more with a baton strike then my pistol would move it.

[K_Mac]

Your friend may be an otherwise intelligent man, but in this case his position is foolish. My momma used to tell me that if you argue with a fool, you're liable to act like one. Give him the facts and challenge him to provide credible evidence to support his claim. Then change the subject!

I think, "take down power" has merit, but it is still a slippery slope...

[Cheapshooter]

The youtube of the episode has been blocked by the network, but Mythbusters did this very experiment. They couldn't even knock down a man sized dummy with a 50 BMG!

[BigJimP]

Its amazing that this stuff keeps showing up in the "culture"....

when it just makes sense if you hang up a bag with 200 lbs of sand or whatever in it...how much do you think it will move if you hit it with a .45 acp at 25 feet...( hardly at all )..... or with 8 rounds for that matter....

[k4swb]

Have him sit in a chair and stick a needle in his butt. When he jumps up ask him how much knock up power the needle has.

[Danoobie]

When you hit live tissue, you may cause a flinch reaction. You may cause an animal to
die, and it may fall over. A person may get shot, and then fall down. But these are all
very different from the dramatic Hollywood "knock you through a wall" scenario.

[RickB]

My father told me if I got hit in the hand with a 45, with my arm extended, it would spin me around.

I am now 57 and do not believe that.

David

I used to pitch on a softball team, and would get three or four screamers coming back my way every season, and catching some, with arm extended, felt as if they could have dislocated my shoulder.
I'd expect any pistol bullet to punch a neat hole in your hand with little energy transfer, but if you were wearing a Kevlar glove you might not "spin around", but you would certainly sense a sudden change in status.

[johnwilliamson062]

Let him have it.
He didn't come up with this on his own. He has heard it over and over from sources he believes to be reliable.
I doubt you will win this one without an extensive demonstration.

[David R]

RickB How much does the ball weigh? How fast is it going?

David

[RickB]

Interesting point, and I was actually going to do some research on that.
The classic "stopping power" ratings - Taylor KO, Hatcher's Relative Stopping Power - were based on momentum, so it should be pretty easy to figure out how a softball traveling at, say, 75mph, compares to a 230gr bullet at 575mph.

Doing the math for "power factor" - bullet weight in grains times velocity in feet-per-second - is easy, so . . .

(9mm) 124 grains at 1150 feet per second = 143 power factor.
(.45) 230 at 850 = 196
(.357 Mag) 158 at 1400 fps = 221
(.44 Mag) 240 at 1200 = 288
(Official softball) 2730 at 110 = 300 power factor

Just for yucks, bowling ball = 2940 power factor

[T. O'Heir]

"...what am I missing?..." Nothing. You're buddy doesn't know what he's talking about. Physics always applies. As mentioned, he's repeating some nonsense he heard somewhere. There's no such thing as "knock down" or "stopping power". Physics doesn't allow it.
"...If the bullet stopped at the muzzle..." The equal and opposite force also stops. There is no more force in any direction. That Newton fellow made a law about that one too.
"...pistol bullet to punch a neat hole in your hand..." Won't be neat, but it depends on what bullet. Mind you, even a ball round is likely to remove most of the hand altogether. Or turn it into an ugly lump of meat, bones and tendons. It will not under any circumstances spin anything.

[Tennessee Gentleman]

So any physics folks here? This is his reply as to the application of Newton's Law.

"Enough with the Newton’s Law crap! When used as an argument it sounds good, and apparently is very popular, but it does NOT work as you suggest. As I said before, that is simply throwing out a fine sounding physics term, but not doing the calculation! Except when the weight of the firearm is equal to the weight of the projectile, the weapon design includes no springs, slides, ejection mechanism or any other force mitigating features, then it does apply as you suggest.

Because Newton’s law say M1V1 + m2v2 = 0 where the first factors are the weapon and the second factors are the projectile, a simplistic look says that it is the same backward force, i.e., M1V1 = - m2v2 . Incorrect. It is the same total force applied across the system, not simply the same force in the opposite direction. First, mass is a constant, while velocity is its own computation, (which includes vector[directionality] as a factor). So, the mass of the weapon is a counterweight to the mass of the projectile. Even the simplistic calculation would go like this: (2.5 lbs)x = (0.0264286)(1180) [I used your BB number here], therefore, the rearward velocity would be 12.4 fps (surprisingly, not 1180 fps as the forward velocity is). However, because of the design characteristics additional energy is absorbed and transferred (the spring changes the vector, for example), the rearward force is further reduced. A very bad zip gun might approach an off the cuff application of Newton’s law, and apparently many, many people use that argument. Newton would shoot you.

Without going into every calculation [I’ve showed enough work here—BTW, I did not just look this up somewhere, I calculated it then used online tools to check my work], for a .45 that weighs 2.5 pounds (an empty standard 1911 is 2.4 so I rounded), the backward force (recoil) is 8 ft-lbs. (Which is less that dropping a 1 lb weight from 3.5 m)

Science is only science if it is applied. “Science” doesn’t tell us anything. Newton does not support the argument, when actually applied."

[zincwarrior]

Originally Posted by Tennessee Gentleman

Brothers and Sisters,
An old Army buddy and I are arguing about the phenomenon called knock down power and I have stated that it is a myth.

Further, I have stated that Newton's Third Law renders the idea impossible in that a round fired with enough "power" to knock down a person (standing normally and not drunk or drugged) would also knock down the shooter.

He says "Ahh, Newton’s third law…it doesn’t apply as you imply. If the bullet stopped at the muzzle with no means of continuing forward or projecting that force forward, the reciprocal force might cause the shooter to be knocked down. But, since the forward force is continuous and dissipated along the trajectory of flight (and the backward force is mitigated by recoil controlling design) said knocking down of the shooter only happens occasionally."

He is a .45 ACP guy.

So, what am I missing?

Well I have Great Great Great...Grandpa's Colt Revolver from the Civil War. The thing is a metal baseball bat, and definitely has knockdown power if he smacked you with it...

Now as a this is a discussion of the .45 ACP, we all know this is of course true. Everyone knows a .45 ACP will blow the engine right out of a car. In fact, I have it on good authority that the dive bombers that sank four Japanese carriers at Midway, didn't have bombs. The crews just threw single magazines from their 1911s out the window and... the rest is history.

"I can run rampant in the Pacific for six months, but then the Americans will start dropping .45 ACPs at us, and we are doomed."
-Yamamoto.

"The Germans have just launched two million men at us at Kursk. Its ok, I've dispatched two men in an American Jeep with an American Tommy gun. The Germans don't stand a chance."
-Marshal Sergei Zhukov.

[TunnelRat]

It seems to me he’s familiar with the equations but not the proper application of them. As much as I would love to type a response in Mathematica, I’m not motivated enough to do so (frankly if someone wants to believe something incorrect, especially a person I have no relationship with, I’m not overly concerned). His very argument can and has been refuted any number of times with video evidence as well as any number of after action reports of individuals receiving hits from pistol calibers and larger and not being “knocked down”, though I imagine he’s the type of person that will come up with his own explanation how in those particular cases the physics didn’t apply or he’d add some part of the system that somehow absorbs all of the force.

It seems now his argument is that the pistol as a system absorbs an overwhelming amount of the force so that while the shooter only feels minimal effect the target will feel dramatically more. I don’t see this as being true in that I don’t believe a recoil operated pistol is absorbing nearly as much as he is intimating and my own experience in shooting steel and wood bears this out. I used to know some physics professors that would probably write something up for him but most have moved to different schools.


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[Bill DeShivs]

Here is my experience dealing with people who have their mind made up and won't be confused by facts-
Both of you agree on a simulation demonstration. Make sure that the demo will prove your point without a doubt.
Then, bet the sucker $100 bucks (or $500 if he REALLY deserves it.)
Take his money when you win.
Remind him of it often.....

[TailGator]

If he wants to completely misinterpret the physics, point out to him that the bullet still will not knock someone down or spin anyone around because it does not deliver a blunt blow - it penetrates. In penetrating, it dissipates its momentum gradually through the resistance of tissues during the course of travel through the body. Or break off the discussion, as several suggested.

[MandolinMan]

Have you clarified what exactly he means by the term knock down power? Even though we agree that its a myth, people uses the phrase in different ways.

For example I frequently hear fellow hunter say things like, " .308 has better knock down power than .223", etc. What they mean is that .308 incapacitates the deer quicker than .223, not that it literally knocks the deer off its feet.

I would be inclined to think that your friend is trying to say that 45acp is more effective at incapacitating bad guys than 9mm, 380, etc. If this is the case, challenge him to appeal to any credible statistics that prove his case. That said, I have met people naive enough to think that shotguns can send people crashing backwards through walls like in the movies...

[Tennessee Gentleman]

He means that a bullet can knock over by it's energy an assailant and that it would not knock over the shooter as Newton's Third law implies. This is because the mass of the handgun would absorb the recoil (to about 99%).

[manta49]

He means that a bullet can knock over by it's energy an assailant and that it would not knock over the shooter as Newton's Third law implies. This is because the mass of the handgun would absorb the recoil (to about 99%).

There is no convincing some people even when its obvious they are talking absolute rubbish. If they are that stupid you have to ask yourself is it worth trying.

[Ricklin]

Your friend has his mind made up. don't confuse him with facts!

My good friend Joe is of the same opinion as your friend. Uh Joe when I shoot that chunk of firewood over there, will I knock it over. Joe: Well of course it will knock it down. Uh no it will not. Unless it is a very light piece of firewood it will barely move, if at all. Joe there is no such thing as knock down power.

Could not shoot there to demonstrate. I'll have to take Joe out to the woods sometime and demonstrate. He has only shot holes in paper.
Ohh and seen too many movies.

The folks that hold these beliefs can be in very deep Kim-Chee if they ever have to defend themselves. They are expecting one shot from a PPK (Joe's gun) to knock over the bad guy.

[mehavey]

If a picture is worth a thousand words...

...then a video is a Britannica volume https://www.youtube.com/watch?v=BgZPusyLeMA