Managed to get the pictures in correct order. Thanks, Johan!

Ulfhere....

"A belief that will not survive a collision with reality is not worth many regrets".

It is entirely appropriate to beat into powder screwy theories that won't bear scrutiny. That's the scientific method.

Of course, the journalistic method is that controversy sells newspapers. It doesn't matter whether it is real or fabricated. Conflict sells. The popular press isn't selling information, it is selling entertainment. It's the nature of the beast.

At one point in our history, a news reporter was sent out to cover a war, and reported back that there was no war going on. His editor cabled back, "You supply the pictures. I'll supply the war."

Chris, I think this test series you describe is an excellent idea. You have posed a hypothesis and devised an experiment to test that question. The photos already provided and the analysis you offer may provide a basis for discussion and debate here. I will stay out of that and let others speak, save to say that I don't think anyone is denying that bullets impacting at high velocities are more prone to failure and mass loss. Your contention, if I understand, is that angular velocity is a significant contributor to this result, perhaps as significant as the force of the impact itself?

I think there were some few points in your last posting that were indicative of a misunderstanding of my statements. Not to be argumentative, allow me to clarify.

Sciuchetti's experiment was designed to test the question of what effect angular velocity had on bullet expansion for impacts having the same axial (linear) velocity. You are interested in that same question, admittedly over a wider range of situations because he was looking at the sensitivity of that effect on his testing method only.

I said that the thermal load was the key element in the failure of the varmint bullets (in air) in a similar fashion to the jet particles. I have seen no evidence that it plays any role in fragmentation of hunting bullets on impact with game animals. That was not my contention. No big deal, you just missed my direction of thought.

The thermal load in jet particles that I described is induced by the process of the jet formation, not the penetration event itself. You can't easily see down into the hole in massive slabs of steel. What I described is disintegration in air, caught on film. So, the penetration of living tissue by bullets is not a significant source of heat due to friction, as you have observed. But as I clarified, I do not see any evidence of a thermal contribution to bullet failure in hunting bullets on impact.

The only reason that I keep referring to the varmint bullets is my conviction (which I am willing to see changed by evidence to the contrary) that stresses due to angular velocity do not significantly contribute to hunting bullet failure at typical velocities. Heat plays no role in this observation. This is not a point of dogma with me, I simply see no evidence. A careful experimental study could make the case.

One thing about copper is that it work hardens. Take soft copper and bend it. Afterward you will have to work much harder to bend it back. Many premium bullets are made with soft copper, but often their jackets or petals after impact are quite hard from the work done on them.

Since you have genuine interest in this question of internal bullet stresses induced by angular velocity and by impact/penetration, allow me to make an offer. I could build a spreadsheet in MS Excel that would allow inputs such as velocity, twist rate and bullet dimensions (including jacket thickness) to be input and that would allow you to examine the resulting stresses at different radii in the bullet. This could then be compared with a failure criterion based on the yield strength of the materials. If you don't have Excel, I could provide the basic equations and let you work out your own means of filling in the numbers. Would that be of interest? This is not a Trojan horse. I encourage scientific pursuits.

quote:

---

Originally posted by mehulkamdar:
http://www.hunt101.com/img/240803.jpg

---

Hmmmmmmmmmmmmmm.

Soil Sacker's shotgun slugs, right Me-hump?

quote:

---

No small arms bullet has 90,000 ft-lbs of energy.

---

The 90,000+ ft-lbs of energy is energy that is placed ON the bullet not of the bullet. It is external forces from forward force and rotational force etc. and I'm no scientist...

quote:

---

Originally posted by wazza:

quote:

---

No small arms bullet has 90,000 ft-lbs of energy.

---

The 90,000+ ft-lbs of energy is energy that is placed _ON_ the bullet not of the bullet. It is external forces from forward force and rotational force etc. and I'm no scientist...

---

Wazza has a point as the bullet is subjected to G forces and the magnitude of these are calculated to be 120,000 to 200,000 G's

I'm no scientist either but here are some figures ( Chris will be aware of them, no doubt )

The mass of the bullet at peak accelleration is between 1100 to 4000 kg ! that is 4 metric ton's....... but then off course we have to understand by definition what units of measurement are and how they relate to the current topic not so ? I'm wondering just how heat factors into the equation apart form the fact that it gets generated by friction?

Now something that has also had me thinking ?

NASA have been experimenting for some years on the effects of ultra fast projectiles....... has to do with impact of ultra fast moving projectiles on the outside skin and protection of space craft and they have ultra fast "guns" (10,000 fps)

Now at these velocities some projectiles evaporate in flight ( turn to vapour) WHY ? Friction???????? well not so cause they attain these velocities only when firing the guns in hyperbaric chambers and when all the air has been sucked out ( ie in vacuums, to negate friction ) Also they shoot the projectiles from smoothbore barrels to negate spin. When spin is added to their projectiles as they did in the initial phases they disintegrate at lower velocities !

Also of interest and spin off of this testing: Questions as to what causes throat and barrel wear? the initial rifled barrel in these tests wore out very quickly but when substituted with the smoothbore there was no erosion ? So is it the powder burn off that causes erosion or is it bullet friction?

More than you've managed to post, Bruce.

Care to post your real name here? The spectacle of bracelets probably worries you.

Wazza, the bullet in flight is subjected to drag and acceleration due to gravity. Neither of these forces results in motion even approaching the muzzle velocity of the bullet, which is what determines its initial kinetic energy state in flight - they serve only to reduce its kinetic energy (drag) and to impart a slow downward motion (gravity). If it were of a magnitude to result in 90,000 ft-lbs of kinetic energy the bullet would be stopped altogether in flight and thrown backward or slammed straight downward into the Earth with great violence. Neither of these forces imparts any appreciable stress to a conventional hunting bullet. Having kinetic energy in free flight (in a vacuum) causes no stress at all. The air drag retards forward motion, so it presses on the bullet and causes some stress, but not enough to deform it.

Posting for Chris Bekker:

Harold,

The question of angular velocity does intrigue me. I observe things, and then theorize the cause in the absence of a manual that I could look up. I do see angular velocity as a contributing factor, but it rests on forward velocity and the twist rate that produce the resulting rpm. Assigning values will probably remain a mystery to me, but obviously the forward force is greater. That bullets fail with thin jackets, I have seen hundreds of times. Thicken them up, and improvement becomes a reality, as shown with my pictures. Gilding metal behaves slightly differently than copper jackets, as they are harder but more brittle, but I have seen both of them fail. Go too thick on the walls, and expansion is either minimal or not at all. Make the lead exposure too small at the tip, and it may not open up. Make it too big and expansion is violent. The bullet's tip take the brunt on impact an if the copper and lead do not flow together (see bond core bullets) with the motion (being pliable) they get ripped off by shear forces (forward & rotational).

My experiments can never be scientific, as I do not have a lab and cannot cover the spectrum of all variables, and secondly, I do not know the all the science behind the scenes, as I am not schooled in that. I can do simple tests that can be indicative. Despite my shortcomings, I have helped people (as an accountant) to improve their bullets with astute observation because hunting is my passion. Being a non-scientist, I consider excessive spin as one of the culprits, but know there can be other factors that involves elastic, plastic and creep strains, also micro-cracking and fatigue (and perhaps another 10 things I know nothing about). I know design engineers are using stress analysis on CAD computer systems - I am not sure if that can be used on bullets to model a bump into a certain resistance, etc. I have seen it when they design gears and aluminum rims for cars.

Do the Excel spreadsheet, but bear in mind the limitations of not having a lab and a huge budget if a lot of shooting is involved with components I may not have. Don't kill it with complexity that is best left for engineers - make it a simple predictive model with a few key variables, and I will give it my best shot. Also explain your formulae and its purported goal so I can follow the logic. Send it to abc@telgonline.co.za . It would be great to model breaking point limits for gilding metal (90/10) and pure copper - but if the lead is not bonded to the walls they will just wash away and if the lead core contains 3% to 5% antimony (like in conventional bullets) it will be brittle and brake when there threshold strength is exceeded. That is why bullet makers prefer to use pure lead for bond core bullets.

If soldiers emerge from the Trojan Horse, I will be standing ready with my 9.3 and 286 gr Rhino Solid Shank bullets, as they are probably one of the most devastating bullets that one can use ... hahah. (check the sterling performance of the Rhino bullet on the far right)

Cheers and have a nice day

Posting for Chris Bekker:

Harold,

Consider another thing when you develop your spreadsheet. I see a multiplier effect with the forward and the rotational force - they don't work independently from each other (not mutually exclusive). They work in conjunction with each other - e.g., as the bullet moves 1 mm forward the 90 degree spin does its work by flaring the bullet a tiny bit open, then the forward motion acts on that and it flares further open and then the cycle starts again until the bullet comes to a stop or exits the animal. So it is not a question of just blaming either the one or the other, these two forces work together like accomplices. That makes it more complicated than one thinks. How does one figure that into a formula? I am buggered if I know. Simple problems with complex answers.

Cheers
Chris

Mehul, You might send this to Bekker.

I'm sorry but your assumptions are based on complete falsehoods. The amount of energy contained in the spin of bullets varies from between 0.4% to 1.0% of a bullets energy. If I figure out how to display scientific notation on this forum I may be able to post you some of the formula's. Most of them are available in a Decent Engineering Physics book just be careful of your unit.
The rotational energy of a bullet can be comparatively easily determined. at 4/10ths of a Percent it's not a signifigant contributer to the terminal performance of a bullet. You need to check out the actual physics before you make any more incorrect assumptions..........DJ

Can one of our administrators assist Chris Bekker in getting his account created on AR?

DJPaintles, personal experience is the best teacher. Let's allow the question to be investigated by a combination of analysis and experiment. Chris is willing (eager indeed) to do some tests, and I will help out with some analytical support as desired. Let's keep an open mind. I know most of us have a predisposition to what the answer is (as people generally do about most things), but let's just proceed as discussed and see how it turns out. We may all learn something new.

Chris, if I were going to construct the experiment I would try to find a specific caliber in which I could get at least three twist rates and a wide range of velocities. That may dictate several rifles, including multiple cartridges for each twist rate in order to cover the full spectrum of velocity of interest (you define what you think is of interest). I know you love the 9.3 mm, but I recommend using a small bore just so that you have the option of higher velocities. Mixing calibers in mid-stream might leave questions.

My suggestion, for what its worth: Pick a particular bullet of conventional construction for which there is a corresponding bonded core design (easy enough). Find a way to test at several velocities (say 2100 fps, 2500 fps, 2900 fps, 3300 fps) with at least three twist rates, or failing that at least two that are quite different (say, 1-in-8 and 1-in-12 or 1-in-10 and 1-in-14). If there is too much difference in the results between velocities you could go with intermediate numbers, but really you are comparing the twist rates. I just think you want to cover the spectrum of impact velocities. These newfangled ultra-magnums do have impact velocities in the 2900 to 3300 fps when used at spitting distance. Bad idea, but its done. Obviously, you would shoot the same load with the conventional bullet and the bonded bullet. I think we all know what is going to happen there, but it will be good data anyway.

Once you have done the basic series, you might want to try a second bullet/caliber combo.

You don't need a lab to be a scientist, so don't worry about that. Einstein did his best work with no formal education beyond the high school level and while working as a patent clerk who liked to read science magazines.

I plan a very simple tool that will just give basic stresses in the material using twist rate, velocity and dimensions. You can vary those values to your liking for diffrent cases and look at the interactions. I don't know a way off the top of my head to make a tool that will readily account for bonded versus not bonded, but you will see stress in each material.

Incidentally, my penetration model is largely done, but I am relying on test results to build functions for expansion and mass loss. Its too hard to predict that analytically and the model would freeze a PC. I'll post it before too long.

During penetration the forces on the bullet will be tension, compression and shear in various combinations depending on the part of the bullet in question and the stage of penetration. What I can do is isolate the stress induced by rotational force and compare that to the stress induced by hydrodynamic pressure. In the worst case they would be additive (as scalar quantities), though forces add as vectors and that may be a lesser amount most of the time. Still you usually see worst case stresses when looking at failure criteria.

quote:

---

Originally posted by mehulkamdar:
More than you've managed to post, Bruce.

Care to post your real name here? The spectacle of bracelets probably worries you.

---

No thanks soil sacker. We're on a septic field. I'll think of you if we go to chamber pots.

(I wonder if this is Cowkiller? Gets angry like Cowkiller. About as bright. How 'bout it, Don? )

quote:

---

Originally posted by Nsiro:
Here´s a link to an interesting article I found today.

http://www.deerstalker.com/bullet_spin.htm

It did got me thinking.

Your opinions ??

Cheers,


Nsiro

---

Just a couple of thoughts from a nonscientific shooter!

By the time you get enough rotational effect to become a serious factor, you are into the realm of unstable bullet performance. I have had small caliber bullets vanish on me several times, and could see the cloud at the point of bullet failure. As the caliber gets larger, it is harder to make this happen (good thing?), and going to other bullet types may stop the failure also.

JMHO, but Nosler hit a pretty good median with the Partition. I have rarely recovered a Partition, yet anytime I have, the nose is gone. Drop the velocity down, and things change. I always used to load them on the high side, never had a problem with them.

One other note,and again JMHO, when the rebuttal starts with a personal attack, well, that is what the roller button on the mouse is for, isn't it?

quote:

---

Originally posted by BBBruce:
[QUOTE]
(I wonder if this is Cowkiller? Gets angry like Cowkiller. About as bright. How 'bout it, Don? )

---

Don and several other members here know who I am, have spoken to me, and I have had beers with more than a few.

If you think I get angry because of your silly posts, you're a bigger idiot than I knew you already were. I do not hdie behind a false identity as I do not have to fear the laws of any country. I do not hate the USA because I am not a criminal under this country's laws like you definitely are.

And, keep your shit to yourself. This is my last response to you - fart as much as you can, Petomane - that is all you could ever produce.

Posting for Chris Bekker:

Sharing some of my experience with you:

I mentioned in a previous post that bullet design can play havoc with a bullet's performance.
The Claw round nose bullet is an example of when a particular design does not work as intended -
i.e. to provide straight-line penetration, retain most of its weight, does not loose petals and open up
without over-expanding as that would impair penetration. 3 animals were shot with a 375 H&H, using the
Claw 300 gr RN (round nose) bullet. Muzzle velocity was down loaded to 2,250 fps and the distance was
about 60 paces for the Gemsbok and 25 paces for the warthog.

Animal Mass retained Expansion
Gemsbok 1 151 (50%) 2.6 x

Gemsbok 2 227 (76%) 3.2 x

Warthog 141 (47%) 2.0 x

It is clear that opening at the tip of the bullet is too small and the curvature is such that the bullet
flattens instead of opening up and this is aided by the inbuilt weakness of the cannelure as it folds
there, squeezes some lead out there and the folding takes place. The same bullet in semi-spider
form does not do this. Also the momentum is too high for 1-mm walls, but that we do not see it here
because of the bullet not opening up, but it is evident with the spitzer. Thicken the walls up to 2-mm
in the spitzer has provided the right performance, just like I illustrated previously with the 270-gr 9.3
bullet.

Penetration was shallow ( because of over expansion) and the 2 gemsbok had to take multiple shots
each, except for the warthog. The picture shows the following:

Retrieved bullets, from left to right :-

1) 375 Claw - Gemsbok 1 - 50% weight retention

2) 375 Claw - Gemsbok 2 - 76% weight retention

3) 375 Claw - Warthog - 41% weight retention

4) 458 Claw - 500 gr - sectioned view to show 1-mm wall thickness
By comparison Rhino features a 2.8 mm thick wall

5) 458 Rhino - 360 gr - 97.5% weight retention - 1.9 x diameter expansion, shot into
a sand wall at 11 paces with a 45-70 Government @ 1,750 Fps

6) .375 Barnes-X - 300 gr - 90.3% weight retention - 2.0 x diameter expansion shot
into a sand wall at 100 paces - MV = 2, 330 fps, impacting at 2,048 fps.

The lesson here is that expansion must be arrested at some point as overexpansion inhibits
deep penetration (3.2 x ) and a good weight retention alone (76%) is not sufficient to be effective.
Construction is important to ensure that the bullet opens up in a controlled way, progressively it must
become stiffer (to cater for higher impact velocities) and it must retain its petals to cut a long and wide
wound track. Hope you enjoyed this.

Regards
Chris Bekker

Posting for Chris Bekker:

This is an array of 7-mm bullets that I fired in my 7 x 57 mm into a wetpack at 25 yards. The attached picture tells the story of the 4 bullets that I tested.

1) Far left - As always you can expect sterling performance from the Barnes-X bullet - no weight loss and a perfect mushroom. You can clearly notice how its petals, that are thinning towards the front, are spiraled by the induced twist, showing the twist-force present on impact. In fact, one can see the twisting better on the Barnes-X than on conventional bullets or the thick-jacketed Rhino bullet. How 'insignificant the "4/10 ths of a percent" of the forward energy the twist is I am not sure, but it bends those petals that you cannot bend them back by hand and remember these petals are stronger and thicker than the those of thin-jacketed bullets.

For those damning critics that say the 7 x 57 mm has no virtue - let me enlighten you; a 175-gr Barnes-X bullet out-penetrates a 286-gr 9.3 mm bond-core bullet (bigger mushroom). Any antelope, up to a 2,000 lb eland will fall to it, and that has been proven a couple of times proving the deadly combination (and with low recoil). People are just amazed when they actually see themselves that such big game are being killed so effortlessly.

2) Second from left - The Nosler Partition will almost always lose its front core, disintegrating in the target. The rear core is protected and provides retained weight ( approx. 65%) to ensure acceptable penetration in most cases. A compromise hunting bullet in my humble opinion. The new Partition Gold bullet now provides a bonded front core to enhance weight retention and to provide a more sturdy mushroom. Currently the thin petals fold back close to the shank and invariable pieces of the jacket is torn off.

3) Third from left - The Claw bond-core bullet, made from 1-mm copper tubing. At 7 x 57 mm velocities, its weight retention is good (99.4%) and it forms a nice big mushroom - a nice hunting bullet at a very economical price. I have not checked this bullet out at 7 mm Rem velocities, but expect some deterioration.

4) Far right - The Sierra Game King bullet - a misnomer in my opinion as it is everything but a bullet intended for game and definitely not to a kings taste. The lead-core disappeared and disintegrated completely - all I could find was the this peace of jacket - 28.5% retained weight. Penetration was shallow (3.5 inches), as it lost most of its weight and thus its momentum on impact. Then the factory has the cheek to call it a "Game King". Again the thin petals just fold back close to the shank. What would happen at 7 mm Rem Mag velocities, not to mention what the 7 mm STW would do to it? Petals are also torn in an uneven fashion. Penetration was totally inadequate. Most other thin-jacketed conventional bullets behave similarly - outdated and just not good enough. Remember, the bullet is essentially doing the killing!

Well, there you have it in a nutshell, and this is exactly what you can expect in game and in some cases even worse when you encounter bone. Pick your bullets wisely and start to reload, if you don't do it already.
Enjoy!
Chris

Posting for Chris Bekker:

Bullet construction of various 7 mm bullets:

Don't look at bullets from the outside - you won't learn much. Sectioned views will give you very good clues as to what you can expect in the field. The attached photograph shows from left to right the following bullets - Impala, Lutz Moller, Rhino, Sierra Game King, PMP ProAmm & Hornady Inter-Lock. In my previous post I showed some recovered bullets from the wetpack. Please note the thin jacket of the Sierra bullet in comparison with the other bullets. The Lutz Moller bullet is an expanding solid, whilst the Impala is a non-expanding solid with a sharp diameter-size cutting edge providing an effective wad-cutter type wounding effect. The Rhino features 1.9 mm walls tapering somewhat to the front to aid expansion. The Sierra has .45 mm walls right through like most other conventional types. The ProAmm thickens towards the mid-point to arrest expansion. The Hornady features slightly thicker walls than the Sierra. In my previous post I mentioned the general poor performance that one can expect from conventional bullets such as the Sierra. Let me summarize the features of these frangible thin-jacketed bullets:

1) Dismal weight retention ratio's
2) Ineffective mushrooms
3)Fragmentation causes meat mincing and bruising
4)Shallow penetration
5) Likelihood of wounding game on angled shots
6) Possibility of long follow-ups and losing of game in brush country

As ethical hunters I believe we have a duty to use effective bullets to ensure one-shot kills. We as hunters need to holler at the factories and tell them that we do not want their outdated bullets - we need to publish the pictures in all gun magazines - the paid journalists dare not do this. Nothing stays the same over a 100 year period - not even shaving blades ( from a single blades to 3 blades, with pivoting heads and a stripes of lubrication). Why should bullets stay the same? After all, the bullet still remains the cheapest item of the hunt. Enough said.
Enjoy.
Chris.

I think Mr. Bekker may be right to some degree; bullet spin may contribute to some extent to disintegration of the bullet.

But I also think his calculations cannot be correct:

To reach "total force" or "energy on "bullet", it is incorrect to MULTIPLY muzzle energy and bullet rotation energy. What do you get by multiplication? Certainly not a significant value expressed in "Ft-lbs", but some number expressed in Ft-lbs X Ft-lbs or "Ft-lbs Square".

To my (very limited) understanding of physics any formula to calculate total energy should be an addition, not a multiplication.

I think that by multiplication any impact of bullet spin is vastly over-represented.

Extreme example: shooting bullets through a barrel with no rifling will result in Zero spin and Zero "bullet rotation energy". Multiply this with the muzzle energy, and then you will get a "total force" or "energy on bullet" of ZERO!

fuhrmann

Here is the link to the spreadsheet tool for calculating angular kinetic energy and the stresses induced by the rotational acceleration.

Bullet Angular Equations

I have made several screen captures of the tool, which follow with the text.

You only need to input the bullet mass, velocity, barrel twist rate and bullet dimensions (all in the highlighted blue boxes). All of the calculations are automatic. The bullet figure will show the shape for your dimensional inputs as a check and the tool will calculate the mass so you can make sure it matches what it is intended to be. I have included several material properties for typical bullet materials.





You can make practically any bullet shape or design, however the equations will not work properly unless you keep the ogive and boattail inputs as being for truncated conic shapes and the cylindrical inputs as cylindrical. In other words, if you decide not to have a boattail then make the boatail section length to zero and have the cylindrical section be the base of the bullet. For monolithic bullets the core is set to zero radius for the cylindrical body and to zero density for the nose cavity.

The main result of the first page is the calculation of the mass moment of inertia, which is necessary to derive the angular KE and forces. You'll note that the kinetic energy associated with the angular velocity of this bullet is only 9.6 ft-lb, or less than 0.5% of the total kinetic energy of the bullet.



This quantity is used on the second page to make a plot of the core stress at its maximum radius and of the jacket tangential (hoop) stress at its interface with the core.



The core pseudo-pressure or core stress is the radial stress in the core resulting from the acceleration imparted by the angular rate. If this value exceeds the yield strength of the core then it can deform (pull apart) due to the angular rate. Since the core is solid and has strength it resists deformation.

The tangential stress is that resulting in the jacket material from the retention of the core mass. Unless the core material is in the yield state, the jacket really feels next to nothing from the core. The calculation assumes that the core is fluid. Actually, it would be closer to correct to subtract the core strength from the pseudo-pressure before calculating the tangential stress. There are different stress directions in the jacket, but the tangential is the highest. This is the worst case condition.



The third page compares the pressure exerted on the outer edge of an expanded bullet (assumed 2X expanded diameter) due to its spin rate during penetration. I will frankly confess that this calculation is wrong - actually the spin rate used here is the nominal rate at the muzzle. The spin rate during penetration has decayed for two reasons: 1) very slightly due to air resistance, and 2) dramatically due to the conservation of angular momentum as the bullet expands. However, since that reduction in spin rate depends on the changing mass moment of inertia, which is dependent on the radial mass distribution (which occupied nearly all of the first page to calculate and which varies by design and impact conditions), I decided to just use the nominal case for purposes of comparison. As you can see, the pressure felt at the outer edge of the expanded bullet due to the angular velocity is not enough to deform the bullet in itself, not even soft lead. It is sufficient to bias the flow of material which is deformed by the much higher dynamic pressure due to linear velocity, so you sometimes see curled petals.



The linear velocity and angular velocity are decoupled once the bullet leaves the muzzle. Each can change without changing the other. In penetration the only coupling is caused by the expansion, which forces the spin rate to decrease.

If you look at the graph you will see that the radial stress induced by the spin on the lead core is not enough to cause even a soft pure lead core to be pulled apart until the velocity is roughly 1400 m/s (4600 fps). That bullets disintegrate in flight at velocities less than this is then due to a reduction in the yield strength and to a critical failure of the jacket. While the stress in the jacket resisting this accleration induced pressure-like force is much higher, the strength of a jacket is also very much higher (based on my modeling I would estimate between 160 MPa and 200 MPa for hunting bullets; less than 1/4 hard, but a good deal more than the annealed condition). Varmint bullet jackets that fail in the air are most likely damaged (resulting in stress magnification) or very soft.

In terminal mechanics, the dominant source of stress and strain is the linear velocity of the bullet. Penetration velocity is less than the flight velocity and the front and rear portions of the bullet do not move at the same velocity until the hydrodynamic phase of penetration is completed (bullet deformation has ceased). This is usually within just a short distance, but by then the velocity has dropped considerably, to roughly 550 to 650+ m/s. However, the spin rate has diminished in large measure due to the rule of conservation of angular momentum and will have completed only about one revolution (or less) by the time that the bullet has stopped deforming in most instances.

Time to end of hydrodynamic phase: ~0.2 ms
Rate of rotation: ~20K rad/s
Total rotation: ~4 radians (out of 2*pi radians/rev)

In short the penetration velocity and angular velocity are not coupled, and it is not only possible to isolate the effects of each, it is necessary for understanding.

You can see that even with very high muzzle velocities and relatively low penetration velocities, the pressure felt due to angular velocity as compared to that felt from linear velocity is a small fraction. As such, I do not see any obvious evidence that the spin rate is a significant, or even meaningful, contributor to the deformation or break up of hunting bullets during penetration. The dynamic pressure from the linear velocity is responsible for the damage to the bullet as much as to the target and certainly bonded core and monolithic bullets weather this abuse with more success than thin-jacketed conventional bullets.

I will be interested in seeing what is borne out by any testing of this premise.

ULFhere, I kinda figured that you were just toying with your buddy Bekker. Your post again proves the point that Bekker's Psuedo-Science is a crock of &#!+.

Herr Furhman, Your Neighborhood?



Beautiful area, I hope to get back sometime.....DJ

djpaintles,

I am living quite in the Swiss lowlands, between Zurich and Lucerne.
But tell me where the picture was taken - maybe I was there when I was young and daring?

Regards,

Fuhrmann

The picture is one of the ones I took from on top of ZugSpitze.........DJ

quote:

---

Originally posted by djpaintles:
The picture is one of the ones I took from on top of ZugSpitze.........DJ

---

So you are looking into Austria.
I never was on top of Zugspitze, but did some hiking and skiing in the area, long time ago.

fuhrmann

quote:

---

Originally posted by arkypete:
Learned Gentlemen
A question for those that are far more knowledgable then I. Does the depth of the rifling play a part in the frangiblity of the bullet?

---

I recently discussed with a quite reasonable guy who claimed that some rifle just "kill better" than others. The carving you mention and the consequent reduction of the jacket's strenght or sesistance to deformation migth be a possible explanation.

HTL,
In your last illustration, I take it that linear
pressure can also be called stagnation pressure?

Mehul Kamdar,
Could you reduce the size of the pictures you
post? It makes following the thread very
difficult. Or is there a setting that I am
missing somewhere?
Thanks.

Yes, I was using a simplified calculation of the pressure at the stagnation point based on the Bernoulli equation.

quote:

---

Originally posted by mehulkamdar:
Posting for Chris Bekker:

Let me summarize the features of these frangible thin-jacketed bullets:

1) Dismal weight retention ratio's
2) Ineffective mushrooms
3)Fragmentation causes meat mincing and bruising
4)Shallow penetration
5) Likelihood of wounding game on angled shots
6) Possibility of long follow-ups and losing of game in brush country

As ethical hunters I believe we have a duty to use effective bullets to ensure one-shot kills. We as hunters need to holler at the factories and tell them that we do not want their outdated bullets .

---

What's all this WE business?

Personaly I have found over 100's of deer shot that using a well balanced conventional soft point or ballistic tip at conventional velocity out of conventional rifles kills deer dead - end of story!

Why in the hell would I want to ask the factory to sell me at huge extra cost a bullet that is going to retain huge amounts of weight etc merely to bury itself further in the ground.

We don't all hunt kudu in the wilds of Africa, a fallow (in the UK in the US read White tail) will be perfectly killed by a standard 243 87gr hornady which doesn't even have an interlock. Who cares what it looks like at the end providing it nearly allways exits and provides a sufficient volume (note I've read Ulf's excellent treatise) wound channel.

I also really don't hold with this reduced velocity (under 2,600fps) business. Perhaps if you are shooting Eland in the veldt but a roe buck at 250m needs a full velocity bullet for trajectory purposes. I see no difference in damage between a 90gr 6mm ballistic tip starting at 3,250fps and a 7mm 139gr soft point starting at 2,800fps.

I have seen an example of "Total Force"

Example number 16.2a

I hit a deer so hard this year at about 80 yards that the total force;
1) lifted the deer off its feet (hoves) and then
2) rotated the deer 180 degrees before depositing it upside down backwards from where I shot it.

Think this is real good example of total force being a product of kinetic energy times rotational energy. But may come closer to proving that total force is a product of Kinetic energy times the square of the rotational energy. Ya no like e=mxc2 maybe TF=KxRt2

PS: That deer never kicked! What did Jack O. say about 270s?

Chris is a difficult person to engage in debate
or discussion because he switches position and
train of thought so seamlessly. From his writings
in this thread alone we see:

He denounces wet paper testing when others do it:
"I say a real scientist should be more careful to base his opinions just on wet paper"
"I dared to criticize his unscientific and confusing wet paper shooting"

He accepts wet paper testing when he does it:
"bullets that I fired in my 7 x 57 mm into a wetpack at 25 yards."
"In my previous post I showed some recovered bullets from the wetpack."

With his own posts of upwards of 400 words, he acuses others of:
"A long explanation to bolster a weak argument."
and states that:
"I talk straight ... not like you that loose the readers in long and incoherent explanations."

He is a master in the art of the mixed metamorphosis:
"The induced torque of bullet spin works 90 degrees against the forward force"
"the centrifugal force is triggered and the bullet is torn open"
"The same bullet in semi-spider form does not do this."

and has difficulty keeping track of things:
"Penetration was shallow and the 2 gemsbok had to take multiple shots
each,
except for the warthog.

He states:
"You can dance around other people with your double talk, but not me."
But on the subject of science his opinion is divided.

First he denounces science
"despite me telling you that it was a simplistic guide,
you insisted to evaluate it on a scientific way."

"I don't need your "scientific" dribble on bullets and wounds on game."

Then he demands science:
"The methodology must be explained, software
used and mathematical techniques employed"

"it is not scientific to test a bullet outside its performance band"
"If we want to be scientific, we need to do a scientific test"
"I need to see the hard scientific evidence"

He does not want to be a scientist:
"Bekker stated categorically that his theory was not science"
"My formula was merely a method, admittedly non-scientific"
"I am going to spit on you scientists if I am proven right"

Then he claims to be a scientist:
"AS SCIENTISTS we cannot leave any room for opinions and apparent logic."

Finally he explains his position:
"any potential reader is taken around the mulberry bush to a drunken state"
"Fuckit man, I cannot make it clearer than this"

.

Based on oberservation, I am convienced that both twist and velocity has a definate effect on killing power and bullet integrity, and one can observe a twisting on some expanded bullets if the spin is violent...

George Hoffman and I used to spend hours discussing and testing this, we called it the spin game...Never came to anything positive other than it happens...

Alf,
The answer is centripetal.

As far as bullet spin and terminal performance is concerned, this
is a problem associated with bi-metallic bullets and I have not
used one of those on an animal since 1993. After the umpteenth
bullet failure on a kudu in 1992, I figured that technology must be
capable of a better way to make bullets.

One fact our experimentation with monometallic bullets has proven
without any doubt, is that it is better to use a monometal bullet
shorter than required for a particular twist rate than longer. If
jacketed bullets are susceptible to break up from tight twists, and
I do not know if it is so, then it is just one more problem I am
thankful I do not have to deal with when designing a new hunting
bullet. Monos thrive on short for twist rate combinations at hunting
distances.

One valid point Chris makes repeatedly, is that all jacketed lead
bullets have a design window within which they work best. This
window is generally over a fairly narrow speed range and also not
at speeds that go much beyond 2800fps. Take a jacketed lead bullet
beyond what it was designed to do, and it will let you down. Who
cares whether it was because of multiplying the length of the boat
tail by the number of spark plugs in the hunting vehicle? If we have
to discuss such fine lines, the bullet is out of it's depth.

With the early (and some still current) monometal bullets, the window
within which they deliver good terminal performance has moved higher
up the speed scale. With HV bullets we have again lowered the bottom
parameter to that of bimetallic bullets, while keeping the upper parameter
where we have become accustomed that it should be with monometal
bullets. Life becomes simpler, hunts become more successful and
discussions such as this become less serious.

quote:

---

Originally posted by djpaintles:

quote:

---

Originally posted by Ulfhere (HTL):
Reader Beware: Chris Bekker is a poseur and not competent to address technical matters in ballistics. He misuses valid scientific terminology to lend credence to his spurious theories. Force and energy are not the same, but Bekker doesn't know how either applies to the mechanics of bullets in flight or in penetration. He also seems unaware of the principle of conservation of energy. How can a .375 H&H bullet have 90,000 ft-lbs of energy? There isn't that much energy contained in the propellant that launched it. Bekker's calculations are invalid in terms of essential mechanical principle, in formulation and in resulting units. Moreover, his arguments are invariably of two stripes: 1) hypothetical cases drawn from these invalid calculations, or 2) hearsay. I defy anyone to find evidence of hard data in any of Bekker's writings. So, let me provide the oft-quoted disclaimer: "For entertainment purposes only".

Actual experiments show that internal stresses on bullets due to angular velocity (properly expressed as radians/second) only causes problems in terms of disintegration when the bullet is very small and also absorbs a lot of heat from friction in the bore or has an extremely thin jacket (think varmint bullets). In either case material failure can result in spontaneous disintegration in air.

Angular velocity does have a beneficial (but very slight) effect on hunting bullets in terms of promoting expansion and (to a greater degree) in keeping solids point forward. I have never seen any evidence of a detrimental effect on any conventional bullet across the range of typical velocities (less than 3500 fps). Bekker's entire premise is predicated on the unsubstantiated claim that the .375 H&H is unreliable due to a fast twist rate and/or high velocity. Examine that claim and you will doubtless agree that it is immediately suspect.

---

ULFhere is absolutely correct. If you will take the time to read any more of Bekkers Psuedo-Scientific Baloney you can see that he pretty makes up equations to prove whatever pre-conceived notion he has. I find it amazing that he spent enough time to write as much different falacious crap as he did on his website. I've never met him, seen his stuff before and have no previous bones to pick with Bekker other than the stuff he is trying to pass off as scientific analysis is a bunch of made up Excrement.............DJ

---

What he said...

Certainly angular velocity, energy and forces contribute something to bullet deformation. The question is "how much?". I am still waiting to see any evidence that it is significant or even discernible at the velocities of interest and in hunting bullets. It may be, but I have seen some evidence to the contrary and in the context of the original discussion I don't see any basis for concern (a .375 bullet at 2550 to 2700 fps from a 1-in-12 or 1-in-10 inch twist barrel). The Scandinavians shoot lighly constructed 6.5 mm bullets at those speeds in 1-in-8 inch twist rifles with perfect success. I just don't see any basis for concern or suspicion. If it were there a great many very successful loads and rifles wouldn't work.

If we start talking about a light bullet of conventional construction with an impact speed over 3000 fps, maybe so - but I will bet more than a dollar that the impact forces in the axis of penetration will destroy that bullet long before the angular rate causes a problem, so its a moot point. When somebody does a test series at "normal" velocity (2000 to 2800 fps) with conventional bullets in two twist rates that are significantly different (at least 4 inches apart) and the slow one is significantly less impaired on recovery than the fast twist one, then I will sit up and become interested. Likewise, when someone can show a bonded core bullet going to bits at high impact velocities on the same basis while the slow twist bullet holds together, then that will be compelling and interesting. Until then, I remain more persuaded by what I have seen to date, which seems to indicate that its not significant.

I am not dogmatic about this question, I just want to see some evidence. I also don't want to give Bekker a hard time just for meanness sake. He has a different perspective on things and that's fine. I'm not out to change the world, that's too great a task. I made a mistake in taking a shot at him instead of just making the case about his argument. That set this off on the wrong foot and that's my fault. It might have boiled over regardless, but that's neither here nor there.

When someone comes up with some convincing evidence from a careful test we all will have something interesting to discuss. Then someone else can go off and try to repeat those results and if they differ we will see the all the accusations and name calling all over. That my friends is science just as surely as the experimentation, but not my favorite part.

quote:

---

Originally posted by Gerard:
Alf,
The answer is centripetal.

---

Gerard: thanks, you were the only one that bit on this one and you are off course correct

Now for the next question:

What happens to the "mass" and "weight" of the bullet when the bullet is subjected to linear acceleration and / or then rotational acceleration?

Does the "mass" increase and what about "weight"

Does this have an effect on terminal ballsitics?