Home Forums Hunting & Shooting General Big Game Knock Out Value

Taylor came up with a formula that he used to compare cartridges for elephant hunting. I'm sure many of you are familiar with the formula:

(W/7000) x V x D
W= weight in grains
V=velocity in FPS
D= diameter in inches

I think that there's a minor flaw in this formula. Many of us know that when you double diameter of a bullet you get 4x the frontal area. Therefore I propose this formula. (Variables are the same)

(1/2 D)squared x V x W

I believe this would give a better (as in more accurate) figure.

What do you gents think?

At some point in the impact of bigger bullets penetration becomes limited. Taylor killed many thousands of animals with countless cartridges. I think with his back ground and experience I would stick with his original idea where dangerous game is concerned. As soon as you use softponts on big game predictable bullet performance with math is meaningless. The shape, weight and direction of penetraion with curving projectiles changes anything you may have calculated anyway.

It's the same with folks raving about sectional density and how important it is in penetration. That only works on paper. Take a Nolser partition for example. It's SD number is meaningless 5" into the game because the front of the bullet will be missing. Not that it's a bad thing but the SD only counts before impact and that is the "magic number" so many people quote. SD only counts with solids it's a more or less worthless measure with anything that can expand or changes its length to weight ratio aftet impact.

JJHack
I disagree with your thing about sectional density. If a bullet expands to double diameter, which will pennitrate farther, a 150 grain from a 270 or a 150 grain from a 30-06? The 270 of course, because it didn't expand as wide.

I think my method more precise, but maybe I just am missing something. Please tell me what I'm missing.

Taylor makes it very clear in his first book (though not his second, which is far more popular) that the KO formula only applies to SOLID bullets and very large game, particularly elephants. Supposedly it reflects how long a certain bulet will render an elephant inconscious, with a head shot that misses the brain.

Despite this very narrow purpose of the formula, hunters have persisted in applying to any cartridge and bullet in the known universe.

I have also known long-time African PH's (such as Finn Aagaard) who said that in their experience, Taylor's KO formula didn't even work with solids on elephants.

MD

The calculations involved with sectional density are a function of the length to weight ratio of the bullet.

Since most folks are using this to apply it to internal performance on game animals, that shape must be maintained to make the calculated comparison work, or have any value whatever.

Soft point bullets lose their shape almost instantly upon impact so the calculated sectional density of the bullet is no longer what was calculated unless it's a solid or monolithic bullet. Unfortunately even those will bend and deform so the entire calculation of SD is only a measure of bullets prior to being shot.

How does a mathmatical measure of performance help to judge a projectile when it cannot be confirmed after the impact? It's only a measure of function before work is done!

Your analogy between the 270 and the 30/06 is also in error. Nobody can know what the expansion will be between two bullets of identical weight unless hiting the same tissue in an identical state. That ain't gonna happen!

Consider the rest of the issues. The 30/06 will be about 100fps faster at the muzzle then the 270 with a 150 grain bullet. This is typical,.... handloads will vary but factory ammo from similiar guns will prove this out. Even loading manuals will show that the 150 grain bullet will be faster from a 30/06 then a 270 where max loads are listed. Each gun will vary a bit as will temps and seating depth etc. The baseline is that the 30/06 bullet will leave the barrel faster for your example. At point blank to 100 yards or so will the additional speed push the 30/06 bullet further through the soft tissue, even with it's greater diameter?

Even though it leaves that barrel faster it will lose speed faster with a lower BC then the longer 270 bullet. So impact speeds will be similiar down range. Do you think that the dimater difference at the start will make a measureable difference upon impact with the mushroom size? They will each enter with a bore diameter hole, and then continue on with expansion. At some point the animals fitness, angle, weight, age, muscle tissue, adrenelin, sex, hair thickness, fat layer, water retention, etc. etc will play a roll in the way those bullets expand. All those issues play a far greater roll in which one ends up bigger then the minimal difference in starting diameter!

I noticed you have posted quite a lot recently and have had a lot of questions about these kinds of topics. I guess your a bit new to the details of bigger game hunting(maybe not?) however you have come to the right place for guidance and experience with most of the things your wondering about. This site is loaded with experienced big game hunters from across the USA and in My case outside the USA.

If I can offer one piece of advice to you. There are a lot of people who are after instant gratification in big game hunting. Trying to do to much to fast is a sure sign of this. If you have not failed at the hunt a few times the success has far less meaning. Heck most of my education has come from failure. ( of course going to the PH academy in RSA was a big help too!)

I remember the post about using the 243 for elk. I just cannot help but see that as trying to work the margins rather then doing the work. You gotta remember that big game hunting is not like fishing where we try to see how big a fish we can land with the lightest equipment. Big game hunting is serious and involves the life of a precious animal. That animal if not handled absolutely perfectly with your choice of gun and shot etc. will die a miserable and sickening death. There is no catch and release( well I do have this with Rihino dart hunts but thats another story) When you squeeze the trigger you gotta know the results before you do.

I'm glad you have come here and have posted so many questions. Much of this is well hashed out over the last 10 years on the net. It's always nice to see and hear these things to refresh what is right and wrong for other new visitors. It's also important for the younger less experience folks who may visit but never post.

Remember there should be some effort and failure to appreiciate the acheivments you will have down the road. Don't worry about working your A$$ off and coming home empty handed. It's that part of the sport, and skill that will develope your character and give you the pride of accomplishment when it comes together.

On ave the 150gr 270 will out penetrate a 150gr 30-06/308 using similarly designed bullets (i.e. partions). They have similar velocities, usually, heavy for cal bullets (150gr 270) are of sturdier construction than standard bullets (150gr 30-06). That alone gives them an advatange. The SD advantage is just an extra.

IMO, to compare anything it needs to be apple to apples. The best starting point for that again IMO is similar SD's. Amazingly enough, for the common deer calibers the "best" bullets have amazingly similar SD's and those that "explode" on contact or "pencil through" share similar SD's (BT's excepted and maybe TSX's).




Most?? You, sir, are a master of the undestatement.

Let me restate my thing with the 270 and 30-06. Lets try a 35 caliber 200 grain bullet. This bullet has a rather low SD and therefore is only marginal for elk sized game. Yet a 25 caliber with a 200 grain bullet! That'd be pennitrating much farther than 35!

Also about SD. If you have a 35 with a bullet weighing 200 grains (Softnosed) it will not pennitrate as far as a 310 grain softnosed of similar construction.
SD also helps with maintaining velocity.

JJHack,
Would you tell us more about this dart Rhino hunting? Seems like one of the stupidest thing anyone could do.

264win,
When comparing .270 and 30-06 SD's it is the 180 grain 30 caliber that is comparable in SD's with the 150 .270 bullet.

JJ,
I have to agree with you on SD. To me it has always seemed the most worthless of all statistics. I could not care less about SD when the bullet sitting in a box or flying through the air. The only place SD matters is after it impacts the animal. After impact, the SD of the bullet has no relation to the bullet before it impacted since it's a different shape.

Even two identical bullets will have different SD's after impact since they will react differently depending on exactly where they hit.

SD doesn't take bullet contruction into account. I'll bet a week's wages that a 120gr 7mm X will out-dig a 150gr 7mm GameKing more often than not, regardless of impact velocity. That even though the SD numbers say the GameKing should have the advantage.

264win, I think I'm going to bow out of this. I've tried to explain it apples to apples but you keep changing the playing field. You cannot bring into the formula bullets of different diamters and different construction and expect comparable results. Your comments about 200 grain soft bullets and 300 grain hard cast cannot be compared because they are not the same construction. No more then comparing a Nosler BT to a Swift A frame. There may be bigger issues here then you can learn in a few posts and what I'm willing to sit here and type out. Plus it does not seem to me that you're really willing to learn about,...... as much as you ask about. It's one thing to want to learn and understand something, and another to debate it without the knowledge or experience needed to communicate on the subject. The best I can offer is to re-read the text with an open mind and try to comprehend it fully. Don't think of ways to argue it, just read it and learn from it.

I'll just let it go and you can sort this out for yourself. As far as the Rhino darting I'm not sure I want to go into a business that you already have preconcieved notions about. It would be one thing for you to ask a polite question about it. It's entirely different when you respond that is it the stupidest thing you have ever heard and yet you know absolutely nothing about it.

Have a good day and I wish you well with your hunting endeavors.

JJ- I agree with your statements but I'll nitpick the above one. SD is calculated by dividing the bullet weight by the diameter squared. So it's more of a weight to diameter ratio. A 150 gr. .308 bullet has the same SD regardless of shape or length.

264- SD doesn't directly reflect a bullet's ability to retain velocity. You're thinking of Ballistic Coefficient. A 165 gr. round nose .308 bullet will lose velocity at a faster rate than a 150 gr. spitzer of the same caliber. Even though it has a higher SD.

In theory a bullet with a higher SD should penetrate deeper than a lower one because it SHOULD have more momentum. But as JJ pointed out there are a lot of ifs in that theory. Impact velocity, jacket opening size, bullet construction etc. conspire against using SD as a predictor of penetration.

264, I'm confused on a couple of things in your post starting this thread. Hopefully you can clear them up. Would the diameter in your formula be the caliber diameter or the expanded frontal diameter? Also, you offer your formula as a "better (as in more accurate) figure." In regards to what? Penetration, ability to kill, or ?????????? Thanks for clarifying.

dale

Dale, agreed with the diameter to weight ratio. I guess in my mind weight is proportional to length where indentical bullet design/construction of the same bore diameter are concerned. The physics remain the same regardless of the terms chosen to discuss this. Even though you have accuratley pointed out the "exactly correct" terminology. Thanks for pitching in on this.

Sorry guys, I havn't been clear with what I mean. When I mentioned the 200 vs 310 grain bullets I was thinking of bullets of the same construction.

Also about the effect of SD on a bullet's ability to maintain velocity, I was assuming that you guys would assume that the bullets had the same weight and same coefficent of form.

In the formula to calculate the frontal area of a bullet is Pi*R squared (R= 1/2 Diameter)
The number my formula gives is a number to do the same thing as Taylor's KO value, but to be more precise. This formula was supposed to be used for a solid's ability to knock out an elephant with a near miss to the brain, just like Taylor's formula.

I wish that the thing of expanding bullets hadn't come up. (I get defencive sometimes, and I have on/off ADD) Sorry everyone about my lack of clarity with everything.

True, as long as you're keeping the diameter the same. A 100 grain 6mm has a higher SD than a 150 .308, but the 30 cal will have more momentum if they're traveling the same speed, and probably out penetrate, if construction is the same.

I think momentum and construction take over for SD when the bullet impacts the target.

zactly, since momentum=mass*velocity. Thanks for keeping me in line <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />

FWIW:

This web page:

www.rathcoombe.net/sci-tech/ballist...be.net/sci-tech/ballistics/wounding.html

has the "real" scoop on wounding and killing game.

The facts laid out are pretty dang impressive (and corroborate most of what JJHack is saying). That is:

"There are some extremely rarely encountered exceptions to the general rule, but for most purposes the hole caused by a bullet is its only measure of terminal effectiveness. "

Good Shooting,

BMT

The only value in the "Knock Out Value" is to give a better feel for the capabilities of a given cartridge. The actual value is of no consequence, so their is not much point in trying to get a mathmatically better formula. This goes double because this formula does not take into account the type of bullet you are shooting.

I generally cannot remember the exact formulat to compute ft/lbs. I just approximate it by using e = M x V^2. I use this only to compare different cartridegs as this is the only valid use for theise formulas.

Good gawd guys-I'm getting a headache here! I just can't keep up with this technical talk! I'm sure you guys know what you're talking about. I learn something new every time I come to the campfire-but jeez, WHATEVER HAPPENED TO JUST TAKING THE RIFLE OUT AND SHOOTING SOMETHING?!
No offense meant here-please don't take it as such. I gotta go find some aspirin!

well said ConradCA

Some bullet's are by design ment to mushroom at a greater rate and carry the mass of the bullet into the game with out coming apart.....Round nose//flat nose //VLD///spitzer//SWC//
the list goes on...

If you shoot a ..Cape Buffalo with a .700 2000 grain VLD
shaped bullet it's going pass right through it on the other hand if you put a meplat of 50 on it then it's going to drop the
Cape like it was hit by a freight train....
In other word a 2000 grain bullet .700 one mile long moving at 2400 FPS .......next to a 2000 grain bullet 1 7/8 inch/long
in .700 ..It's as plain as the . NOSE on your face's <img src="/ubbthreads/images/graemlins/grin.gif" alt="" />

264Win �

While I understand where you are coming from, you fail to understand the points made so well by JJHACK. Sectional Density alone is a very poor indicator of how a bullet will penetrate, even with bullets of the same general construction. Other factors which come into play include impact velocity, original diameter, final diameter, speed of expansion, differences in bullet construction (yes, even �identical� bullets in different weights and calibers may have significant differences in areas such as jacket thickness). If comparing �identical� bullets like the Partition, for example, the differences in the diameter and weight of the front core could be expected to have a significant effect on penetration.

It has always been my contention that Momentum (Mass x Velocity) plays at least as important part in determining penetration as Energy (Mass x Velocity x Velocity). While specific load data varies, take a 150g .270 at 2900fps and a 20g .350 at 2700fps. The .350 has 24% more Momentum and 16% more energy, factors which you ignore completely in your assertions about SD and penetration.
Last year I shot a bull elk at 213 yards with a .45-70 and a 350g North Fork bullet. The initial SD of the bullet was 0.238 and impact velocity was around 1537fps. The bullet went through the front leg, obliterating the bone and exiting out the back before entering the chest cavity where it obliterated a near rib and shattered a far rib before coming to rest under the hide on the off side. That�s 3 layers of hide, and 3 major bones. The final SD was in the neighborhood of 0.10009. Low initial SD, low impact velocity, and very low final SD. My 20+ years experience on elk with a 7mm Mag and 160g bullets, which have a higher SD than the 150g .270 you want to compare to, leaves me with doubts that the 7mm Mag would have performed as well due to the lighter bullets � even though I have had complete penetration with the 7mm Mag on a big bull at 350 yards, fewer bones were encountered.

You need to look at ALL the factors, not just SD. And remember that, counter-intuitively, it is well demonstrated that additional velocity often reduces total penetration.