Help with an Argument on "knock down" power

[briandg]

I noticed that some posts here compared the foot pound measurements of bullets to actual feet/pound measurements. This isn't a proper use of those measurements. The kinetic energy of a bullet is not comparable to the low velocity heavy weight. The bullet expends large amounts of energy just blowing through the tissues. Hitting a steel plate and expending almost all of that energy moving the plate is one thing, hitting a squishy pile of gunk and spreading that out in damaging the squishy stuff is another. Energy is lost in the splatter.

this is a super duper .44 load. it did a good job on the block, maybe a 30 pound block?

This round will not 'knock down' a man, but being hit that brutally will almost certainly make him fall over. A guy standing on two feet has a pretty tall center of gravity and he's standing on only a narrow platform with weak ankles. Would you expect a guy's legs to go pretty limp when he takes a hit like that?

It all depends on what "knock down" means, and what all of the other language means. Something to think about, were you ever hit by a baseball? 1/3 pound, 60 fps. All I ever did was swear very loudly.

https://www.youtube.com/watch?v=NU6ZKQrfr9M

This second video uses my personal carry load. That certainly failed to knock down the gel, but it really scared it.

https://www.youtube.com/watch?v=PjxSr-TYFVA

[Chainsaw.]

Never argue with idiots, they'll pull you down to their level and beat you with experience......

[RedHoundTargets]

This could kinda be fun to think about but it becomes almost a catch 22 situation.

Newton's 2nd law: basically F=ma (Force = mass * acceleration)
3rd law: all actions have an equal and opposite reaction

With a constant acceleration while in the barrel to propel a bullet from rest to a certain velocity, there will be a steady, not-too-unpleasant force applied to the bullet, and a (equal and opposite) force applied to the firearm/shooter.

If we assume point blank range, and that the bullet does not pass all the way through the target, that same velocity that was reached must be slowed down from its peak back to zero fps by the target.

If the target is soft tissue, the bullet could take even longer to decelerate (negative acceleration) than it took to leave the gun barrel since it is passing through tissue over time. That means it would have lower acceleration, and therefore would apply lower force to the target than it applied to the gun/shooter system.

However, theoretically if the bullet impacted a target that did not give at all, such as some armor steel anchored such that it doesn't move at all from the impact, the negative acceleration of the bullet would be nearly instant. That means a huge number for acceleration which means a huge number for the force applied to the target, which could theoretically knock someone down. Of course the large force was only possible because the bullet impacted something immovable.

TLDR: A bullet could theoretically apply enough force to knock someone over, but only if they cannot physically be knocked over. Catch 22!

[JohnKSa]

How the force is applied, and the properties of the target medium are critical to determining how much and whether the force will actually cause motion.

Here is a quick thought experiment.

Go out to your driveway, take the parking brake off, put your car in neutral and apply 100lbs of force to the car by pushing on the trunk with your hands. The car will move, and if you continue to apply force it will gradually pick up speed.

Now, put the car back where it was, brake off and in neutral and go get a sledgehammer and swing it at the back of the car so that it applies 100lbs of force. Same amount of force applied to the same target but now the force will be used up putting a large dent in the trunk and won't result in any noticeable movement.

[Model12Win]

Larry Potterfield of Midway USA has an excellent series on Personal Defense demonstrating the "knock down factor" of various guns:

https://www.youtube.com/watch?v=6xJD...EB07A4A4DF162D

He is an industry expert and knows what he is talking about. If he uses the term, then it is valid:

"Knock-down factor is the ability of the cartridge to knock down an assailant with one well placed shot." -Larry Potterfield, Midway USA.

[JohnKSa]

He is an industry expert and knows what he is talking about. If he uses the term, then it is valid:

https://www.logicallyfallacious.com/...alse-Authority

This is a classic appeal to false authority fallacy.

The fact that Mr. Potterfield is obviously very good at and clearly very knowledgeable when it comes to making money by selling firearms products does not imply that he is an expert when it comes to terminal ballistics, that he has any special insight into the topic, nor that his use of a term in that field provides any proof that it is valid.

Here's the link that explains what those numbers mean. Apparently, they are someone's idea at Midway USA of how various cartridges should be ranked. In other words, even if one chooses to accept them as valid, they aren't a measure of effectiveness, they are merely a ranking.

https://www.midwayusa.com/content/Ho...ting-Chart.htm

For some arbitrary reason, they topped out their ranking at 400 which means that nothing can rank higher on the list than a .45ACP 185gr JHP +P load. Not even a 12ga shotgun or a .50BMG rifle.

[briandg]

Here are two points.

Red, you applied newton's law, that is correct, but misapplied. Newton's law applies to pool much better. The cue imparts motion to cue ball, to next ball, then all balls are impacted during the break. There is very little energy lost in the process. A pool cue is very heavy, and imparts high velocity movement to the ball, and a enormous amount of other impacts give all of those other balls a share of that motion, the motion is expended on friction and deformation of the bumpers.

The energy in a bullet is conserved, following the other law, conservation of energy. It is simply converted to lots of different forms. Some of that energy is converted to friction that releases energy as heat. Then we have the energy lost when the bullet deforms, as much energy as it would take to hammer in a nail. (Look at blank powered nail setters). The next thing that absorbs energy is deforming anything that it touches, but if you are talking about a lead bullet on steel, obviously, the only deformation of the steel that occurs is on essentially microscopic and extremely low levels.

Blah blah blah, more still, the last I have to point out is that motion is imparted two ways, but only a part is usually transferred as movement. What energy isn't used up in all of those other processes is expended by pushing against the target. In meat, most of that energy seems to be not used in pushing, shoot a gallon of water, it will barely move. Steel applies a lot of energy as movement, but still, a lot of that movement is nothing but vibration, transferred to sound through the air.

So, most energy is expended in other ways while the rest is transferred as push.

You can't 'knock a man over' by hitting him with a bullet, the vast majority of that 'push' is converted into other forms. We like that. We want that energy converted into destruction.

Model twelve, as was said,lets not start up with an argument with one 'expert' against another.

Factor isn't a science term, really. They used some formula to calculate how much energy is available for push, that is obvious and simple, and it would work just fine if nobody used anything but fmj ball.

But once you change a variable like adding a hollow point, The force that would be used as 'push' or 'knock down' is being converted into heat and destruction. No 'knockdown' factors exists that can be applied to real world shootings on anything anything that deforms, or by any item that deforms.

You can transfer motion, per Newton, or convert it. The best science is still inadequate to create a genuinely effective calculator for the effects of a gun on a person. There are too many possible variations in the target or projectile to factually declare a scientific law based on only factors of velocity, diameter, and weight.

[kozak6]

Energy is not conserved. Momentum is ALWAYS conserved.

Even in a perfectly inelastic collision, momentum is always conserved.

Barring overpenetration, it doesn't actually make any difference whether a FMJ or JHP is fired into a ballistic pendulum. Deformation of the bullet and target, noise, heat, etc, is all irrelevant as that corresponds to wasted energy instead.

Midway's "powerfactor" is an ordinal unitless madeup number that doesn't correspond to any physical value.

There isn't enough momentum in a bullet to knock down a person.

And that's fine, as "knockdown power" is a physiological phenomena instead. Consider the "knockdown power" of a groin tap, for example.

[briandg]

Kozak, have you ever heard of the law of conservation of energy?

https://en.m.wikipedia.org/wiki/Conservation_of_energy

There you have it.

You can convert, divert, whatever sort of energy you want into another, maybe undesirable form of energy or work but it is still there, you can't 'waste' energy unless you mean that you aren't getting a desired result.

Your assessment of whatever you are referring to as 'wasted energy' is wrong. Momentum cannot ever possibly be entirely transferred from one physical thing to another, elastic or inelastic, because in EVERY collision there is energy converted from momentum into some other form suck as heat.

But, whatever. Believe whatever you have to believe.

[GeauxTide]

Yeah, lotsa foolishness out there. My two buddies came home from Paris Island Boot Camp in 1968, advising that the reason the 5.56 was so effective was that it starting tumbling out the barrel.......... As far as knockdown, the Taylor Knock Out formula comes the closest to field performance for me.

[briandg]

My two buddies came home from Paris Island Boot Camp in 1968, advising that the reason the 5.56 was so effective was that it starting tumbling out the barrel.

I got really tired of hearing that one too. You would think that an ordinarily intelligent person could look at thousands of bullet holes on paper during boot camp and other training and still believe that the bullets were flying Willy nilly, tumbling through space like every football pass I ever made.

[briandg]

Ed matunis created a scale called the martinis power level that wasn't even an attempt to be scientific, but it was logical and probably pretty accurate. His equation included

Bore diameter
Weight
Velocity
Bullet construction

You wound up with a ke (momentum) number, factors sectional density, then increased it according to bullet shape and function, and the resulting number gave an approximation of how well a round would hurt someone

In this order, he used bigger, heavier, faster, and round, that, or expanding. His numbers said that a Lrn .38 wouldn't work as well as a flat point .45 at the same velocity. I believe that he was right on that count.

His idea that bullet selection should be part of any assessments took thirty years, but right now, it is close to the single most important factor in choosing hunting or defense ammo. The fbi thinks so, as do nearly all other educated people. If you ask them to give up their hollow points, unless some unusual problem exists, they will decline.

[zipspyder]

Smaller 30 caliber bullets need to use the hollow point trick or soft point expansion to be more effective. 45+ big bore calibers don't need that, just a nice wide meplat to get the job done. Pretty basic but a good rule of thumb.

[briandg]

The high velocity rifle used to be available in hunting hollow points, they were exactly like a standard modern soft point, but they bab no exposed lead, a small empty space behind the gameplay, and a tightly closed tip on the jacket. These were pretty much identical to varmint hollow points, but built heavier for big game. Exposed lead contributed to quicker start to expansion and more reliable expansion, so most big game bullets, cup and core, non tipped, etc, are made with some exposed lead.

I have a specimen of a Winchester .270 with that hollow point.

[Mike Irwin]

"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."

I talked to Newton (Issaic AND Fig).

They both say "YOU KNOW NOTHING OF ME OR MY WORK, SIR!"

[hdwhit]

"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!

Ah, yes, the college boys have all those fancy sounding words, but I've got my unshakable beliefs in the gnomes, pixies and fairies.

[hdwhit]

Tennessee Gentleman wrote:
An old Army buddy and I are arguing about the phenomenon called "knock down power" [edited to add quotes]

Before we go any further, how do you and your buddy define the term "knock down power" and how do you propose to quantify and measure it? From what follows your original post in the thread, it seems as if you are equating it to momentum (mass times velocity) and that's a poor proxy as it fails to take into account the many masses that are involved, what velocities are being imparted to them, the time over which this is occurring and the higher order derivatives of velocity such as acceleration and jerk that apply.

Can a bullet knock somebody down.
-- Certainly.
----- I've seen it happen.
--------It has actually happened to me.

Can the recoil of a gun knock someone down.
-- Again, certainly.
----- I've seen it happen.

Does it always do that? Of course not. People aren't blown around the firing range like so many autumn leaves by the recoil of their guns. The discovery of the mechanisms at work to explain why some people get knocked down and others don't and how you would quantify and measure what's going on would be the start of any discussion of "knock down power".

Until you and your buddy define the term, further discussion or analysis of an undefined term using an inapplicable metric is pointless.

Within the last year on TheHighRoad.org, one of the members posted the entire publication history of the International Wound Ballistics Association's Wound Ballistics Review. It's still available and makes for fascinating reading and a thorough study of it would be particularly useful for this conversation as it would provide a practical basis for formulating the concept of "knock down power".

[hdwhit]

briandg wrote:
Momentum cannot ever possibly be entirely transferred from one physical thing to another, elastic or inelastic, because in EVERY collision there is energy converted from momentum into some other form suck as heat.

The OP and his buddy are stuck trying to use conservation or momentum from Newtonian physics with a questionable frame of reference without identifying all the masses and velocities involved and you want to bring the 2nd Law of Thermodynamics into consideration?

That's brave.

[briandg]

It's hard for me to understand. One can only try. If a person talks about energy being transferred and converted to movement, in particular the vibration of a going hit by a bullet, with the going vibrating, the energy of the vibrations being transferred to whatever medium is available, such as air, those vibrations that shake the air are perceived as sound.

There is now the question of

"Since you can't hear anything in outer space, where does that energy go?" If someone hits a gong and they are wearing really good ear muffs, did it really make a sound?

I'm going on 30 hours without sleep and this is making my brain hurt.

[Tennessee Gentleman]

Originally Posted by hdwhit

Before we go any further, how do you and your buddy define the term "knock down power" and how do you propose to quantify and measure it?

Here is my definition I proposed to him earlier. An average sized male standing upright, sober and conscious, is knocked off his feet to the ground purely by the force of the handgun bullet strike. This is not to be confused with "falling down" due to psychological or physiological means.

The FBI says such force would also knock down the shooter due to Newton's third law. The FBI further says that "stopping power" is a myth and the effectiveness of a round should be measured by wounding or medical reasons.

[JohnKSa]

Here's a video showing a man shot at point blank range with a .308 rifle.

He stands on one leg to demonstrate how little effective force is applied by the bullet impact.

https://www.youtube.com/watch?v=aaS_2l8nGdg

If a .308 rifle bullet won't do it, neither will any handgun bullet.

Here's another similar video showing rifle testing against a live human wearing a bullet proof vest.

https://www.youtube.com/watch?v=6x59iN4KMz4

[briandg]

You are right, t.v., I also agree with your definition. Knock down means, literally, knocked down like a bowling pin. fall down is completely different. Man stopped is ridiculous, nothing short of electrocution will ensure that he is 'stopped'. The fbi and other sources refer to an 'ouch' factor. How seriously the round will injure a man at several levels of impact. Will the guy swear loudly and keep on fighting, or will he look down, see his liver laying on the ground and faint? I'd like to have ammunition that will probably shred a lot of the things that keep him alive. I'd like to have it for fifty cents a round, and able to fit into a pocket pistol.

A lot of people believe that such around exists, but the government has banned it.

[briandg]

The idea of the shooter being knocked down is made even more ridiculous by the fact that just the mass of the gun is enough to minimise the recoil f lots of rounds.

[44 AMP]

If it isn't the bullet, then, what is it??

Seriously, if it isn't the size, weight, speed, momentum, or any other factor of the bullet (no matter which formulae are used), then what is it that "knocks" them down??

Perhaps the myth is the idea that it is the bullet that knocks down a live target.

[ammo.crafter]

Taylor Knockout scale.