Taylor Knock Out Factor

You can call it whatever you want of course - the originator of the term is long dead - but TKO is one of the most misused firearms "formulas" extant. Most will think: John Taylor shot a lot of elephants - he's GOT to know what he's talking about! Well, he does. Unfortunately, what he talks about regarding TKO has little to do with handgun (or rifle) hunting game with expanding bullets:

"I do not pretend that they [TKOs] represent "killing power"; but they do give an excellent basis from which any two rifles may be compared from the point of view of the actual knock-down blow, or punch, inflicted by the bullet on massive, heavy-boned animals such as elephant, rhino and buffalo". (African Rifles and Cartridges, pg. xii)

Not quite what most shooters THINK he said, is it? For those who bother to actually read what Taylor had to say, it is clear that his TKO formula only applies to the knockdown ability of headshots into large African game with non-expanding bullets. IMO trying to make such a formula fit handgun body shots into medium game (or people) with expanding bullets is a futile exercise, and that seems to be an attempt to add credibility to the pet opinions of wananabe hunters who desire to "piggyback" onto the reputation of a famous hunter/author.

Most shooters will be very surprised to learn that for medium game hunting with expanding bullets Taylor believed that kinetic energy was as good an indicator of killing power as any other. And this from the pen of a hunter (more accurately poacher) with far more experience than most of us will ever have. Do we believe him when he says kinetic energy is the best indicator of killing power? Do we accept that his TKO formula only applies to head-shots on very large animals with non-expanding bullets, or do we continue to miss-quote him and insist that the TKO quantifies killing/knockdown power on deer and elk (and people)? Thoughts?



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I just compare energy (m x v^2) and momentum (m x v). Lots of energy but little momentum means bullet selection matters more to balance penetration vs energy delivery (327 mag, 30 super carry). Lots of momentum, little energy means it’s probably just about as good in ball as anything else (45 auto).

Playing with calculations is fun, bit there really aren’t huge differences until you get to rifle velocities.

If you want energy and momentum, the 3” 12 ga slug is king.

https://www.luckygunner.com/labs/pocket-pistol-caliber-gel-test-results/
22lr CCI Stinger 32 gr. @ 970 fps = .98
25 acp Fiocchi XTP 35 gr. @ 946 fps = 1.1
32 acp Hornady Critical Defense 60 gr. @ 865 fps = 2.4
None of those bullets penetrate at least 12'' and consistently expand.

https://www.luckygunner.com/labs/self-defense-ammo-ballistic-tests/
380 Hornady Critical Defense 90 gr. @ 910 fps = 4.1
9mm Federal HST 147 gr. @ 973 fps = 7.2
Those bullets meets the desired criteria of at least 12'' penetration and consistent expansion.

How do I choose ammo to carry, bet my life on, what criteria?
-Wouldn't want to get shot with it? Might be true, but nope, that criteria is not gonna cut it.
-Nobody volunteer to get shot with it? Might be true but, still a nope, that doesn't cut it either.
-Better than nothing? Might be true, but I'm not going to settle for that as my selection criteria.
-Taylor Knockout Formula? At least it is based on data, momentum, but its missing something(s).
-At least 12'' penetration and consistent expansion? Bingo. That criteria is what I use to select carry ammo.

Criteria #2 is based on how many of those bullets that meet criteria #1 can I have available before a reload.
How about 5 rounds available? Heck no.
How about 6 rounds available? Nope.
How about 10 rounds or more? Now we are talking.

I read about it on the Buffalo Bore website and thought the TKF factor made a lot of sense when talking about bullets penetrating large critters.

i like what Mr Sundles wrote about it, and as a quality ammo maker and hunter, I think he has good points. It is a short read if interested:

https://www.buffalobore.com/index.php?l=product_list&c=173

That does a good job of predicting how well a load will knock down a steel plate. Has nothing to do with predicting how well it will fare when stopping a living threat.

Does anyone else calculate the Taylor Knock Out Factor when looking at loads and different cartridges

Click to expand...

Nope - never did and never probably will.
The only real calculation I pay any attention to at all is - sectional density.
(which I refer to as the great deliar)

I have my own formula that I use:
1- a reliable handgun 9mm or better that I shoot well
2- HP ammunition from a reputable brand that functions reliably in the chosen handgun
3- Hits to center mass (refer to the FBI qual sillouette target, of 5 zone on an IPSC target.
4- Don't be shy about firing more than once. There's a reason the thing holds more than 1 round. Hopefully you don't have a pirate gun.

Hal said:

Nope - never did and never probably will.
The only real calculation I pay any attention to at all is - sectional density.
(which I refer to as the great deliar)

Click to expand...

But a good expanding bullet has a dramatic reduction is sectional density as soon as it encounters the target. High sectional density indicated good external ballistics but Ballistic Coefficient tells that story better. It has almost no bearing on terminal ballistics since most good hunting or self-defenses bullets have a dramatic reduction in sectional density at the target.

There is no one number that can tell you anything useful, and I would argue very few of us only look at just one number.

The numbers that matter are mass, velocity, kinetic energy, momentum (if we know any two of those we know all of those) and then bullet construction (geometry and material properties). All of these are easy to get. The ones that are hard, in a setting with a living target, is the target itself. The material properties of a living creature are messy and difficult, the target geometry at the time of impact is also very difficult to describe accurately, and finally the most unknown is the will to survive. You can shoot two deer in nearly identical ways with the same gun and one ultimately dies from the wound and the other one survives.

If we make the target an inanimate target especially if its rigid materials then the solution become easy and just requires lots of computer time. Go to YouTube and look up armor penetration simulations. Modern computers with dynamic finite element models can model a bullet impact with a huge variety of targets and accurately predict the resulting damage and penetration. But they still have not figure out how to put the will to live in an FEA model.

Taylor Knock Out is interesting but again it falls into the trap of trying to generate one number to describe a really messy and unpredictable terminal ballistic event.

Some numbers can be guides and the more you have and the more you understand their meaning the better. But you're still better off just going out and shooting stuff. Shoot water jugs, shoot wet magazines, shoot scrap wood, shoot clay, go shoot animals. Then come back to the numbers and they will tell you even more.

-rambling


Compare to the real world

Jump to 7:30 for FMJ against hard armor similar to the FEM simulation.

WisBorn said:

@jmr40 so a 9mm at 8.1 compared to the 10mm at 15.1 has nothing to do with stopping a living threat?

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I like 10mm and have 10mm pistols. That said...
I'll stick with the 9mm I posted before.
9mm Federal HST 147 gr. @ 973 fps = 7.2 - this bullet penetrated 15.2'' / .61
https://www.luckygunner.com/labs/10mm-auto-self-defense-ammo-ballistic-gel-tests/
10mm Federal Trophy Bonded 180 gr. @ 1,227 fps = 12.6 - this bullet penetrated 32''+ and didn't expand .40

As I said, I like 10mm; but, IMO the 147 9mm HST making a .61 hole has better ASAP potential against a human than a .40 hole.
I apply the same thought to a 230 gr. 45 acp FMJ despite it having a higher Taylor factor, IMO a 9mm expanding to .61 has better ASAP potential.
Same shot placement is a given and we are talking human attackers.

mcb said:

But a good expanding bullet has a dramatic reduction is sectional density as soon as it encounters the target. High sectional density indicated good external ballistics but Ballistic Coefficient tells that story better. It has almost no bearing on terminal ballistics since most good hunting or self-defenses bullets have a dramatic reduction in sectional density at the target.

Click to expand...

True enough.about the expansion.
I have to disagree about the terminal ballistics though.
You said it yourself - about the expanding bullet having a dramatic reduction in S/D once it hit the target.

Bullets with a poor S/D initially, are going to only get worse if/when they begin to expand.

Some ammunition manufacturers tout very high velocity & along with that, high energy figures. They get that by using light weight ammunition - ammunition that has a low initial S/D.

I'm very skeptical when the S/D calculator shows a number that Is in the range of nearly unacceptable penetration. Why I like to call S/D the deliar.

The ballistic coefficient - as far as this goes, I don't see where that is a factor at all for 95% of all handgun use.
Maybe hunting at a distance?

The current thinking, as far as personal defense against humans is concerned, appears to be that shot placement overwhelms other factors. I agree, insofar as that a little hole in the CNS is going to work a lot better than a bigger hole in say, a tricep. Having said that, it seems to me that at least from a handgun hunter's perspective, nearly all handguns - especially the typical CCW pieces - are badly underpowered for use against enraged and aggressive 200+ pound animals, be they human or not.

Obviously, the issue is complicated by such ideas as overpenetration, size and weight of the handgun, shot-to-shot recovery times etc., but on the whole, I lean toward the most powerful round I can carry.

Hal said:

True enough.about the expansion.
I have to disagree about the terminal ballistics though.
You said it yourself - about the expanding bullet having a dramatic reduction in S/D once it hit the target.

Bullets with a poor S/D initially, are going to only get worse if/when they begin to expand.

Some ammunition manufacturers tout very high velocity & along with that, high energy figures. They get that by using light weight ammunition - ammunition that has a low initial S/D.

I'm very skeptical when the S/D calculator shows a number that Is in the range of nearly unacceptable penetration. Why I like to call S/D the deliar.

The ballistic coefficient - as far as this goes, I don't see where that is a factor at all for 95% of all handgun use.
Maybe hunting at a distance?

Click to expand...

The classic 38 Special with a 158gr bullet has a better sectional density than a standard 45 ACP 230gr. .179 vs .161 and yet very few people would argue 38 special is better than 45 ACP. 44 Mag with a 180gr bullet has a dismal SD in comparison to either of those examples .139 and setting capacity aside 44 Mag even with a light 180gr bullet is substantially more handgun than 38 Special or 45 ACP. The old Webley Mark IV chamber is 38/200 has in comparison to the previous three cartridges a spectacular sectional density of .219 and yet almost no one recommend carrying 38/200 any more.

My point here and in my earlier post was no one number tells the whole story and if we are honest we ourselves we don't look at just one number.

Real world testing trumps numbers and the numbers only have meaning when they match real world testing. <- This is true for more than ballistics and it is the bread and butter of a good engineer...

Great info, and I understand mostly the counter arguments. But, can we all agree that the most often stated simple ft pounds of kinetic energy is very limited? It seems not to capture the true efficacy of the round.

mcb said:

The classic 38 Special with a 158gr bullet has a better sectional density than a standard 45 ACP 230gr. .179 vs .161 and yet very few people would argue 38 special is better than 45 ACP. 44 Mag with a 180gr bullet has a dismal SD in comparison to either of those examples .139 and setting capacity aside 44 Mag even with a light 180gr bullet is substantially more handgun than 38 Special or 45 ACP. The old Webley Mark IV chamber is 38/200 has in comparison to the previous three cartridges a spectacular sectional density of .219 and yet almost no one recommend carrying 38/200 any more.

My point here and in my earlier post was no one number tells the whole story and if we are honest we ourselves we don't look at just one number.

Real world testing trumps numbers and the numbers only have meaning when they match real world testing. <- This is true for more than ballistics and it is the bread and butter of a good engineer...

Click to expand...

I do tend to agree - about using just one number - - however - I'm still sticking with using S/D first and foremost when looking at ammunition.

The OP did ask about "when looking at loads and different cartridges."
I did respond that I don't pay attention to Taylor - that the only figure I pay any attention to is S/D.

Knowing the caliber - which gives you half of the S/D equation right there - allows just glancing at the bullet weight.
If I'm buying ammunition for my S&W M19, I know I'm buying .357" dia. The package will usually tell me the weight.
That's all the information I need to form some sort of buy/no buy decision.
Having a solid 40 plus years of piddling around with this stuff gives me a good idea of what are decent weights (for my use) in the calibers I shoot.

Let me toss the TKO in here also.
Using the Hornady Critical Duty 124 grain 9mm load the TKO is 7.3
The sectional density is - (I don't want to say dismal - but - it isn't up there where I feel good about it) .141
Now - given those two - the TKO is meaningless to me. OTOH, the .141 S/D tells me the load is a little on the light side and I'd be concerned if it expanded too early that it wouldn't have enough left in it to get to the vitals.

It's all too easy to get caught up in engineering-level documentation.
Then, suddenly, we are all fretting over millimeters, and mere tens of Joules, and random amounts of mass.

Per the medical types, the only difference they can see in dealing with GSW are rifle versus pistol--and that latter is all handguns. That, 5 of 6 GSW who arrive at the ER alive walk out afterwards. Now, in fairness, the medical types lump all GSW together. They have enough work as is without having to detail "peripheral" hits versus COM (which has to do with some peripheral hits being arterial, and more serious than some COM hits; it also has to do with how would you categorize multiple hits, which are common).

Really, as spiffy as a .357 is in a pistol, it's not really a .30-30 or a 7.62x39 or the like. Those latter not being very handy to put in a holster on one's belt being the only real issue.

WisBorn said:

Does anyone else calculate the Taylor Knock Out Factor when looking at loads and different cartridges.

Click to expand...

No one who has an understanding of terminal ballistics. To understand my statement, use the Taylor formula to calculate the "Knock Out Factor" of a 16lb bowling ball rolling down an alley at 24.5 fps vs a .45 ACP.
Bowling ball:
Mass (in grains) - 112,000
Velocity - 24.5 FPS
Diameter - 8.5"

Bowling Ball - 332.2 Taylor Knock Out Factor ((112,000*24.5*8.5)÷7000)
.45 ACP - 15.2 Taylor Knock Out Factor

According to Col. Taylor's theory a bowling ball rolling toward the pins has more than 20 times the knock out capability of a .45 ACP.

I'd prefer to lay down on an alley and let someone roll a bowling ball at me than let someone shoot me with a .45.

I use Gold Dots for .45acp, 9mm and Hornaday critical defense if I am carrying my LCP. After carrying for about 30 years now that is all there is to it for me. I don't feel ANY need to overthink my ammo choices.

MikeInOr said:

I use Gold Dots for .45acp, 9mm and Hornaday critical defense if I am carrying my LCP. After carrying for about 30 years now that is all there is to it for me. I don't feel ANY need to overthink my ammo choices.

Click to expand...

Basically what I carry in 9mm versus .380. Sometimes HSTs too in 9mm.

Sectional density and even TKO get misused often and even more so out of context or in an apples to oranges comparison.

Often, sectional density will be used to judge superiority of one cartridge over another, even cartridges of different calibers and power levels, so that someone can try to hype up their favorite cartridge and try to say that even though it is smaller, it has bullets with higher sectional density so it must be better.

Back when 6.5 CM was gaining traction, some folks would actually use sectional density to say that 6.5 CM was not much different than 45-70 and possibly better than 45-70 for any and all game species. I heard that argument more than once.

TKO, really starts making more sense as a measurement when relatively wide caliber, somewhat shorter for caliber bullets (low sectional density), and of non-expanding design are the subject.

Sectional density and TKO have a place but they are still just numbers.

An anecdote. I have have seen more whitetail deer DRTs with foster slugs than any other bullet type. I lived for a long time in a shotgun zone so I saw a lot of shotgun kills so this makes sense for me. Foster slugs have some of the worst sectional density of all projectiles but they work great on deer. If you get enough projectile weight and enough velocity sectional density does not matter anymore no matter what the game animal is.

Granted now, this is the handguns section so the intended targets of which TKO or sectional density may apply are going to be of pretty known construction and general size. My opinion on this matter is that if you use a heavier for caliber (or cartridge) bullet you will be putting yourself at an advantage, however slight that advantage may be.

Common sense meaning selecting a cartridge suitable for the game hunted and proper placement mean more than any formula. I have read several books on African hunting, particularly Elephants. Several professional hunters killed Elephants with properly place FMJ rounds from military style rifles with military rounds. Of course many also used double rifles in a variety of very high power rounds as well. Some used both. I have killed several dozen deer with a wide variety of weapons. Proper bullets and placement is what works.