In a SA hunting magazine, "Game & Hunt" September 2005 edition, Dr Mauritz Coetzee wrote an article in Afrikaans under the title "Solid bullet dynamics", if translated directly.

One of the points discussed is the stability of the bullet inside the animal.
He goes on to say: "With the initial contact on large bone, a large amount of stress is put on the bullet's tip. This stress originates from the centrifugal force that is placed on the bullet's tip." (Direct translation.)

My question is now how large is this "large amount of stress" if thermal energy and energy due to rotational velocity together account for only ± 5% of the total energy or forces at work when a bullet is penetrating an animal?

Certainly kinetic energy, the other ± 95% part of the the total force at work, must be responsible for far more in determining the bullet's stability in the animal.
This part of the forces at work is not mentioned by the author.

Lastly, is it really centrifugal force that Dr Coetzee is referring to in this instance?

These are questions coming up in my mind when reading his article.
Can members of the forum clarify these questions perhaps?

The author, would be the best person to ask what his thoughts are/were, in the article.

Hog Killer

I can't wait to read this one..

quote:

Originally posted by Jagter:
=Lastly, is it really centrifugal force that Dr Coetzee is referring to in this instance?

These are questions coming up in my mind when reading his article.
Can members of the forum clarify these questions perhaps?

I can answer the last "question"...

No. Why? because "centrifugal force" doesn't exist. All forces act in a vector, not an arc or radius, vectors CAN be, on a macro scale, interpolated by humans into an arc. This is a misnomer,like "a bubblebee can't fly" or using the word "irregardless"

jeffe

There are several pages on this website http://www.grosswildjagd.de/english1.htm which explain the physics of how a bullet penetrates through flesh and bone.

Also, there was an article on http://www.gscustom.co.za about the same subject, but I cannot find it right now.

.

Try this article:

http://www.gsgroup.co.za/articlepvdw.html

.

With the initial contact on large bone, a large amount of stress is put on the bullet's tip - Logically this must be from the bullt travelling forwards I do not understand how centrifugal force comes into this.

.

quote:

Originally posted by ALF:
Jeffeosso:
...And just to put the record straight the force in the projectile is not centrifugal it is centripital...

Alf,
EXACTLY.. jagter asked if it was centrifugal force... that "force" doesn't exist, so the answer to his last question is "no"

jeffe

Now that we know it is not a "centrifugal" force as was stated by the author, but rather a 'centripetal' force at work, which still forms part of the smaller 5% of the total force, we can move on to the next part.

quote:

Certainly kinetic energy, the other ± 95% part of the the total force at work, must be responsible for far more in determining the bullet's stability in the animal.
This part of the forces at work is not mentioned by the author.

Has this larger part (95%) of the forces at work, obviously in collaboration with the smaller portion, any major influence on the solid bullet's stabilization while travelling in the animal?

Jagter,
Glad I could help clear that part up for you and answer your question.

jeffe

Thank you Alf, I have heard of small and fast bullets falling apart in flight and your explanation is logical for that but with solids is that possible? Comparing it to a subject like flywheels. If a flywheel is modifeid for higher revs it is lightened around the circumference. This makes it less likely to fail under high revs than removing materialfrom the middle somewhere. But a flywheel is a big round flat rotating object. A solid bullet is more like a shaft and a shaf fails because it is out of balance or gets smashed agains something like on a rally car on rough roads. I do not understand how a solid bullet fails because of rotation forces when it smashes a bone. Maybe the rotation force can ad to the break up a little but is the smash not mostly responsible for the bullet breaking? I thought solid bullets are made from stronger material for the purpose that they must be much tougher than bullets used to shoot smaller animals. Another idea is that the rotation of the bullet must also be easily reduced by the contact on the animal. It is easy to stop a shaft or brake disc from spinning by applying pressure to the circumference like when you work with it on a lathe. But if it falls off the workbench it is another matter especially if your foot is under it.

.

With the energy due to rotational velocity ('centripetal' force) now reduced to a minor factor as pointed out below by
Alf:

quote:

This is why the effect of spin is not that important because any numeric derivation based on the revolutions within the target boils down to this very low value of only two,

it certainly looks if Rat Motor summed it all up in his following question:

quote:

....... but is the smash not mostly responsible for the bullet breaking?

That again takes me back to one of Alf's other posts where it is confirmed that the larger 95% part of the energy actually does the work and I therefore derive that it will also cause damage to a poorly designed bullet when it hits large bone.

Alf:

quote:

c) Kinetic energy tranfer to the target, if the target is non elastic it will move with impact ( this fact is seen with the shooting of falling plates) In elastic materials the kinetic energy is absorbed by the elasticity and no movement actually takes place there is however internal movement in the form of:
d) mechanical energy transfer. (Important )

Mechanical energy = force needed to overcome resistance to penetration through volume change of the target medium in front of the projectile. ie there is a force ( energy ) used to push the target medium away in front of the penetrating projectile.
This is directly related to Drag so the magnitude of Drag or alternately: this mechanical energy determines the size of the tempory cavity.
This drag force is further directly velocity dependent as shown by it's numerical derivation.

Am I right if I then conclude that stabilization of the solid bullet in the animal depends on at least two factors, namely:
(i) Kinetic energy in the form of mechanical energy transfer, as well as
(ii) good design of the bullet?

Comments please.

I do realise that this design part can fill volumes, but let's leave that for those who know for now.

.

Alf, I don't think anyone is advocating a true cylinder for a hunting bullet. Both the BRidger and GS designs are truncated cone designs, which your reference indicates is the deepest penetrating. This, of course, differs from the Barnes and Rhino designs which are hemispherical round noses with a little spot ground flat.

.

Hi,

Where are the engineers or scientists? This is their terrain ...

This discussion supplements the discsusion that I am having with Gerard on stability of bullets with a value in excess of 2.5 (he now claims only the .375 caliber)to provide straigh-line penetration. He claims that as the stagnation force drops then this value of 2.5 can be lowered, like for a 9,3 x 62 mm.

I am surprised that Gerard has not jumped in to educate you chaps. Gerard claims that he has the calculations, but he is not going to share them. (State secret, my ass)

Where are the boffins with at least a masters degree in engineering and have applied experience in this field. I think at this level we ordinary guys need the expertise of these oaks.

Chris Bekker

Alf, you are 100% correct if you say:

quote:

You are mixing concepts. Stabilization vs factors is tissue damage.

It is simply not because of ignorance for the ballistic science theory, but purely because the mixed concepts are the end products (including all the ballistic theories and whatever else) I as a hunter have to use and deal with in the form of ammunition to achieve my goals, namely to successfully kill the game I set as my target.

The fact you have stated that there are still theoretically, unjustified ballistic principles that need to be studied and written after thorough research, I leave with all due respect for yourself and all the other experts to investigate and come up with a valid solution to all that is to it.

However, what is disturbing to me is the fact that self-appointed ballistic experts publish articles based on completely wrong concepts in hunting magazines, as we have seen in this thread, and then expect readers to accept it unconditionally. Hence the reason I started this thread.

Thanks to all the members who participated and helped to answer my founded questions in respect of this specific article.

quote:

stagnation force

quote:

we ordinary guys need the expertise of these oaks.

How do the words of that old classic song go? " I talk to the trees, but they don't listen to me...."

.

Thanks again Alf. I wonder why the author of that article attaches such importance to the force generated by the spin on the bullets? I got hold of the magazine and some of the other things in that article also looks strange. I suppose the question is really whther one should worry about this or just ignore it and shootfor the shoulder anyway.

Can the Guru explain to us how stagnation pressure works and how it destroys (work against) the stability of the bullet (SF values), if we pitch the velocity at 3 different levels ... say 2300 ..... 2600 ..... and 2900fps with a 300 grain solid bullet in .375 caliber.

Is this stagnation pressure more or less or the same for an expanding solid, like a Barnes-X or a GS-HP? Does it also work negatively when a bullet expands or is it in the bullets favour to assist with the set-up of the bullet. Huh?

Please do not keep it a secret in the interest of mankind.

Chris Bekker

What is a Truvello and is of any use after it has ben shot?

Truvelo is a company that builds hunting, target and sniping rifles. They build a fancy custom rifle for me on a 1909 Argentine Mauser action. I like this rifle quite a lot - its a in 7 x 57 mm.

So I shoot a Truvelo product.

Chris Bekker

Bas Alf,

Die anner bas hy se djy moet hom die bandjja SF he, because why daai stagnation pressure hyy es ok bandjja, annners daai koeel hy loop nie reguit nie mar hy loop sos die dronk man en hy val om. Eish!

My nam hyy es Jonas

The whole question of how stagnation pressure works against the stability of the bullet has still not been explained (decpite repeated requests to Gerard) and nor the various factors at work to provide stable straight-line penetration in flesh.

The answer does not solely lie in SF values ... or does it? (Alf, you have actually already given your answer on this one)

Chris Bekker

Chris,
Using a language that is not understood by the vast majority of members, is disrespectful and a breach of forum manners. But then, manners is not one of your strong points so it is taken whence it comes.

Give us the definition of stagnation pressure. No helping out here Alf, let Chris do it on his own.

Gerard,

You are a real prick, I have read all Luz Moller stuff on it, as well as all Alf's postings on the subject on AR.

You need to explain how SF as a numeric value influence stability in a target .... in an animal .... in flesh .... not air for which WinGyro was designed !!!


I am giving it to you in English - not Kantonese. Your answers have dropped to a pathetic level, but you still have an opportunity to answer and rectify your silence on the matter.

I am waiting ....

Chris Bekker

Quote:

"So how does SF as a numeric entity exactly play in the penetration equation? is it of any consequence at all and if so what is the relative contribution." .... Alf

Reply:

Gerard you should not worry about Alf helping me. You should actually answer Alf's question, which begs the question you are avoiding like a sly fox that has stolen some meat of the farmer's table. I am just wondering how we can prevent that Alf is actually helping himself?

I am waiting ... and I guess Alf is also waiting ...



Chris Bekker

quote:

Your answers have dropped to a pathetic level ......

There is a direct correlation between the level of an answer's intelligence and that of the question being asked!


According to all authoritative sources, "Stagnation pressure is the pressure a fluid exerts when it is motionless."

Even if one assumes air as a fluid (partially correct), one cannot find any application to bullet ballistics because the "fluid" is always in motion around the bullet, in a relative sense. The same applies when the bullet is travelling in body "fluid" (partially correct).

There is one area where "stagnation" occurs in bullet flight, however. It is the area at the base of the bullet where the moving air rushes in around the bullet base, creating a tiny pocket of extreme turbulence, the stagnation zone.

But the stagnation zone has no effect on stability that is of any significance whatsoever.

Thus 'stagnation pressure' is a non-existing 'force' in ballistic science.

.

quote:

"So how does SF as a numeric entity exactly play in the penetration equation? is it of any consequence at all and if so what is the relative contribution." .... Alf

Alf,

I am not sure if your question is in vain, but I am trying once more to solicit an answer. Anybody is welcome to answer - even the prins of Arabia.

Chris Bekker

The original question was:

quote:

The whole question of how stagnation pressure works against the stability of the bullet ........ (1 September 2005 13:34 post by CB)

I take it that you agree with the following:

quote:

According to all authoritative sources, "Stagnation pressure is the pressure a fluid exerts when it is motionless."

Even if one assumes air as a fluid (partially correct), one cannot find any application to bullet ballistics because the "fluid" is always in motion around the bullet, in a relative sense. The same applies when the bullet is travelling in body "fluid" (partially correct).

quote:

According to the Bernoulli equation stagnation pressure is the pressure measured at the point where the fluid comes to rest (motionless). It is the sum of the static pressure and the dynamic pressure.
The dynamic pressure is not really a pressure at all: it is simply a convenient name for the quantity (half the density times the velocity squared), which represents the decrease in the pressure due to the velocity of the fluid.

At this 'standstill' (stagnation/motionless) point stagnation pressure has no effect on the stability of the bullet.

CORRECTION on previous post: "Stagnation pressure" does play a role in terminal ballistics.

'Nuther pi$$in contest.......

Chris,
Where did Alf ask: ""So how does SF as a numeric entity exactly play in the penetration equation? is it of any consequence at all and if so what is the relative contribution."

Gerard,

Alf posed the question on page 9 of "ongoing discussion - 380 gr Rhino and it was posted 24 August 2005 19:26 when he wrote to me and subsequently I have repeated the same question to you a few times as you are the one who needs to answer this question, as it relates to your theory that you hold up for us ... to either accept with proper motivation or to reject if not motivated properly.

Chris Bekker

.