.

Different approaches;.... Controlling the variables..Vs..allowing real world variables to exist.

http://www.tradgang.com/ashby/...ow%20Penetration.htm ...


"Penetration data collected from real shots, into real tissues, is not a static measurement. Outcomes differ from shot to shot, as the uniformity of tissues encountered change. In the real world it is impossible to control all the variables, and one does not wish to do so. Those variables do exist. They will be encountered.

The scholar of abstract science will cite that this testing methodology includes too many variables, but it is precisely because of the multitude of variables that it is necessary. When dealing with infinitely complex variables, only ‘outcome driven’ information analysis, from a multiplicity of data, provides usable results. This is why the medical community commonly uses ‘outcome driven’ studies.

A commonplace example of these differing test approaches occurred with the development of automobile air bags. Engineers did enormous static testing with crash dummies, controlling all variables, before air bags were introduced.


After the introduction of air bags into production automobiles, outcome driven analysis showed that significant numbers of adult humans were being injured, and sometimes killed, by air bags during their deployment. An even larger number of children were being injured or killed. Static testing had indicated the deployment force would be safe. The ‘reality’ outcome was not as the static testing had predicted...."



Artificial test media-[crash test dummies] did not indicate the real world lethality of airbags to humans.


"An absolute ‘predictor’ of arrow penetration, on every shot, is impossible. Outcome driven analysis from real shots, into real tissues, does, however, give a definitive picture of any given arrow’s incidence, tendency, and frequency of occurrence of events during tissue penetration. Testing in a uniform medium does not. Having tried both approaches, I feel certain that it is only through the use of outcome driven results that reliable indicators of an arrow’s likelihood of performance under real hunting conditions can be developed."....


...The SECTIONAL DENSITY of an object of round (cross sectional) profile is defined as the mass of the object divided by the square of its diameter. The heavier the object is in relation to its cross sectional area, the higher its sectional density. The higher the sectional density, the less the amount of frontal surface area (per unit of its mass) that is presented to the target, and the less of the target’s ‘matter’ (relative to the penetrating object’s mass) that will be displaced by the passage of the object through the target. This translates into a lower level of resistance on the frontal area of the projectile.

If the mass of an arrow is increased without changing its external dimensions, it will weigh more per unit of cross sectional area. Its sectional density will be increased, and it will penetrate farther with any given applied force.

Note that the sectional density refers only to the resistance on the penetrating object’s frontal area and the amount of ‘matter’ displaced in relation to its mass. In tissues, an arrow’s “shaft drag” is also an important feature influencing penetration. Shaft drag results from the frictional forces between the arrow shaft’s surface and the substance being penetrated.

Shaft drag is one major reason that arrow penetration test into artificial test media often differs from actual results derived from testing on real animal tissues. Most ‘target materials’ rely heavily on shaft drag to stop the arrow. They are made from materials specifically chosen and designed to ‘close down’ around the shaft, exerting the maximum possible shaft drag. Muscle fibers, on the other hand, tend to retract, actually spreading apart, when cut by a sharp broadhead.

When cut, muscle tissues also release blood, which lubricates the shaft, reducing the coefficient of friction between the arrow shaft and the tissues. This reduces the drag on the shaft. These biologic reactions are a major reason why accurate and reliable measurements of hunting arrow penetration can only be achieved through testing conducted on live (as when actually hunted) animals, or VERY freshly killed animals.

Even when testing on freshly killed animals, physiological tissue changes occur rapidly, and testing must be done within minutes of death. If the time lag is longer, results become erroneous, due to changes in tissue resistance forces encountered.

quote:

Originally posted by 303Guy:
It might be argued that it's proof of the effectiveness of a high SD.

Actually, the effectiveness of that arrow is rather impressive! ...

or proof of the effectiveness of high efficiency [low velocity & low drag]...How much momentum & velocity does a broadhead have compared to a HV centrefire?



You could have two arrows[projectiles] with the same velocity,weight & Sd,fired into the same media, but achieve different penetration.

...giving one a more gradually sloped blade angle together with sharper cutting edges, would offer more efficiency/less drag/increased mechanical advantage,..thus greater penetration.

One of the same reasons for making FN solids with a tapered-conical nose,rather than a totally straight walled wadcutter profile,...correct?

However the FN rifle bullet still remains relatively blunt compared to a broad head[which has a cut on entry tip]...the FN is design more to intentionally push/displace/smash/pulverize, or breakup a larger volume of matter[relative to its X sectional area], rather than more efficiently "slice" its way throught with minimal drag/less resistance.

I would describe a FN solids conical design-geometry more like the bluntness of an "Icebreaker hull" Its designed to pulverise resisting matter, or create a particular volume of passage["wound channel"] through the ice.

Interestingly, IceBreakers can have a bubbler system that shoots air around the hull to make its passage through ice more efficient,by reducing friction[air is a lubricant]..is that not similar to the benefits/effects of cavitation around a bullet?

Of course an identical arrow, with the same sd as the one that penetrated well, will give no penetration at all if just one condition changes: Speed becomes 0fps.

Capo

We are on the same page about the 'event'.
we might use different words and slightly different contexts , but its the same page.
The unfortunate part is that not everyone is necessarily viewing the event from muzzle to rest in the target thru the same eyes or the same understanding of the physics of the 'event' and have different perceptions of what causes different portions of the event.

IMO the thread has been very useful in providing frank discussion of the event from muzzle to rest in the target & what really does influence performance in the penetration of the target. Choice of projectile construction manipulates the nature of the tradeoff between penetration & severity of damage adjacent to the penetration path and whether that is a single penetration path or multiple paths with the dynamic change in SD of the projectile &/or its parts having the most influence on the nature of the penetration event & the damage caused , where it is caused, in the penetration event as a transfer of energy from the projectile at impact into the target.
Hopefully, along the way , it explains why penetration performance is highly variable and which projectile 'styles' are more predictable over a wider range of circumstances.

The discussion got a bit "wobbly" at times , but a great thread discussion none the less.

Methinks the OP got a lot of value from his excellent question.

sorry for the late reply, I have been out of town for a couple of days.

quote:

Originally posted by Gerard:
Of course an identical arrow, with the same sd as the one that penetrated well, will give no penetration at all if just one condition changes: Speed becomes 0fps.

Yes, without any propulsion force being applied there would be no momentum to give a projectile the potential to penetrate....No momentum = no penetration.

When one places a high Sd centre fire bullet say on a hard plastic or wooden table surface, there is no penetration taking place, despite there being a force applied to the projectile,..that being gravity.

Two reasons the bullet does not penetrate the table;
1. the lack of sufficient force/momentum in the bullet, and
2. sufficient resistance present in the tables matter.

Place an arrow on the same table and it will also not penetrate, just by force of gravity.

Sufficiently increase the force on the rifle bullet and it will penetrate.
Sufficiently decrease the strength/resistance of the matter that the bullet or arrow rests on and it will penetrate.
Change[increase] the Sd of the projectile[even just the initial entry tip section] and you will require less projectile momentum and/or less reduction in table material strength to achieve penetration.

Now change the material that supports the static projectile;

If one gets a frame or tube with some clear plastic lunch wrap stretched across it,then gently places a high Sd rifle bullet on that taught plastic sheet [nose or base first], it will cause the sheet to deflect somewhat, but highly unlikely the bullet will penetrate.

Now get an arrow with pointed & sharpened broadhead [same weight as rifle bullet],and hold it vertically in static position with its tip down, just touching surface of the plastic food wrap material. Don't propel the arrow, but just release it to the force of gravity...and the sharp tip of the arrow is most likely to penetrate the plastic wrap material.

The projectile movement-momentum created due to force of gravity,together with the low resistance of target material,contribute to material deflection/followed by penetration of material.
A contributing factor is also the much smaller X sectional area/much higher Sd, of the arrow at time of tip contact/entry.

In other words, someone standing on your hand wearing a large flat surface area soled sneaker- is not going to hurt you as much as someone of the same weight standing on your hand wearing a thin pointy heeled stiletto....

It seems that to boil it down to a nut shell we are dealing with the difference in opinion versus proven fact.

465H&H

I should have been more clear in this statement. I was refering to the conclusions of testing of terminal affect,not SD.

465H&H

It is not required to write pages of explanations and opinion plays no role.

The weight of a bullet is not the sectional density of that bullet.
The caliber of a bullet is not the sectional density of that bullet.
The weight and caliber of a bullet determines the sectional density of the bullet.
The sectional density of a bullet is not the momentum of that bullet.
The speed of a bullet is not the momentum of that bullet.
The weight of a bullet is not the momentum of that bullet.
The weight and speed of a bullet determines the momentum of that bullet.
The momentum of a bullet does not determine the penetration of that bullet.
The caliber of a bullet does not determine the penetration of that bullet.
The construction of a bullet does not determine the penetration of that bullet.
The shape of a bullet does not determine the penetration of that bullet.
The momentum, caliber, shape and construction of a bullet determines the penetration of that bullet.

You can ignore gravity but that does not make gravity go away.

quote:

The momentum, caliber, shape and construction of a bullet determines the penetration of that bullet.

Roger that. And of all those variables, only the area and mass of a bullet determines the Sectional Density. ERGO, as a practical thing rather than navel gazing, SD means nothing.

Roger has only been putting petrol in his car & ignores the oil & water, that explains why the wheels don't go round any more..........minor details in how far the car traveled before it stopped.
............He He.

Damn details, they always keep getting in the way

Roger is right in one way tho you can kid yourself that you can ignore SD by choosing
a bullet with a known construction and demonstrated mushroom behaviour . The reality tho is that choice of construction & demonstrated mushroom behaviour is inextricably an expression of the SD dynamic of the bullet in the penetration event.
As a practical decision it works to a point.

Where the point is follows........


G
velocity relative to the target resistance ????

we can ignore target resistance , but then we can't argue about gelatine & wetpack vs live tissue any more , what a waste of a good argument........and why where we hit the target determines performance.

How susceptible the bullet construction is to a variation in the resistance of the target and hence change in dynamic SD determines how consistent the penetration performance is a variety of circumstances.

The statement:
" I have used bullet XYZ all my life & it has never failed to do the job"
is a valid statement , but its only valid in its particular context of useage by the person making the statement.
Changing just one of the actual parameters that affects penetration performance will change that performance. The bullet ignores nothing, it reacts to every aspect of its physical dynamic in its environment, whether the shooter ignores them or not.

Sooooo........we have talked about SD influence between muzzle & target & in the penetration event.

There's one part of the total event we haven't discussed :-
What's the effect of SD between chamber & muzzle ????.

quote:

What's the effect of SD between chamber & muzzle ????.

You may have found the only practical consideration SD may have.

.

quote:

Originally posted by ALF:
Trax:

yes !

The "mistakes" made in the interpretation of the tests are numerous but most probably the greatest error derives from the fact that behaviours are reported that are not tested for.

As I have tried to show over and over it is a two way street.

Only the bullet behaviour is tested for in the simulation, not the target behaviour and even then only certain behaviours not all.

So if there is comment bullet expanding or fragmenting etc etc then that part is ok, the minute there is reference to the amount of trauma done to the paper stack or gelatine or reference to this likely being a better killer than that, as observed by the amount of damage to the target then the test is invalid, no matter how many times over you repeat the test !

It is a systematic error in the methodology employed.

Yes I agree that the amount of damage to the target material would constitute a measure of lethality in living tissue but sadly simulation testing does not test for this..... this is the problem and people do not seem to get this.

The hole you see in gelatine and the hole in paper after shooting is not representative of the amount of damage done in various tissues. This is why basic science in ballistics is so important.

Just to illustrate here is a picture posted from the terminal thread



This is the "trauma" done to the paper.

Simple questions:

1. What caused this damage ? By that I mean by what mode of action did this occur? by the bullet striking the target------

2. Do you see this behaviour in living muscle , or bone or organ tissues? In other words if you shoot your animal do you see this destruction and mass of devitalized tissue ejected from the target ? that doesn't matter--as you have been informed many times it IS possible to correlate data given enough datum points-contrary to your innuendo Michael has never asserted that his medium reacts the same as an animal--just that you can correlate some aspects of the event.

This whole thing to me is amazing because this thread on terminals is so important it has been made a permanent fixture on AR. Not surprised that you are confounded-it isn't that hard to do

So anyone wishing to find out about ballistics who googles Terminal behaviour is going to get this popping up on their screen. They may actually believe that what they see there is how things happen ? Yep because it is exactly as represented and is repeatable

I cannot wait to see some kid at school presenting this for fact when asked to write a term paper on ballistics ! He would get a A-

Still don't get it do you--


SSR

quote:

The statement:
" I have used bullet XYZ all my life & it has never failed to do the job"
is a valid statement , but its only valid in its particular context of useage by the person making the statement.
Changing just one of the actual parameters that affects penetration performance will change that performance. The bullet ignores nothing, it reacts to every aspect of its physical dynamic in its environment, whether the shooter ignores them or not.

The same logic is used by those that shoot big game with .223s.

.

quote:

Originally posted by Jim C. <><:

quote:

What's the effect of SD between chamber & muzzle ????.

You may have found the only practical consideration SD may have.

IF thats the case, why then if you consider SD has a practical consideration in an acceleration event , do you consider SD has no practical consideration in a deceleration event.

Can you describe its consideration in the ballistic acceleration event .
Lets pick a single case & a single powder load as constants.

Lets say with a 30.06 case that way we have a bunch of calibres & SDs commonly available as variables with that case size & the same load .

30-06 example 1. Same load and bullet throughout with only the COL varying. With the maximum COL the rifle can have, loading single shots into the chamber, the pressure will be 'x'. As the COL is shortened, pressure and speed will decrease progressively until a point is reached where pressure and speed will start increasing again. So, a range of pressures and speeds are achieved while the sd of the bullet remains exactly the same.

30-06 example 2. SMK and old Barnes X without the coating, both are 180 grains and both have identical sd numbers. To get the same speed from both, pressure, powder weight and barrel time will differ. To get the same pressure from both, speed, powder weight and barrel time will differ. When loaded with the same powder charge, speed, pressure and barrel time will differ.

Why is sd important with internal ballistics?

quote:

Originally posted by Gerard:
30-06 example 1. Same load and bullet throughout with only the COL varying. With the maximum COL the rifle can have, loading single shots into the chamber, the pressure will be 'x'. As the COL is shortened, pressure and speed will decrease progressively until a point is reached where pressure and speed will start increasing again. So, a range of pressures and speeds are achieved while the sd of the bullet remains exactly the same.
You are trying to say that bullet mass per unit area does not matter . A deliberately stupid example.

30-06 example 2. SMK and old Barnes X without the coating, both are 180 grains and both have identical sd numbers. To get the same speed from both, pressure, powder weight and barrel time will differ. To get the same pressure from both, speed, powder weight and barrel time will differ. When loaded with the same powder charge, speed, pressure and barrel time will differ.
Here you are trying to say that you can change everything else and ONLY SD is fixed and it should yield the same result. Another dumb example

Why is sd important with internal ballistics?

You can't pick on just THE parameter you want to ignore and ignore ALL OF THE OTHERS AT THE SAME TIME.

quote:

You are trying to say that bullet mass per unit area does not matter . A deliberately stupid example.

I am not trying to say, I am saying that, despite bullet mass per unit area remaining the same, many other factors play a bigger role with internal ballistics.

quote:

Here you are trying to say that you can change everything else and ONLY SD is fixed and it should yield the same result. Another dumb example

Again I am not trying to say, I am saying that despite bullet mass per unit area remaining the same, many other factors play a bigger role with internal ballistics.

BTW, you still owe me an answer. Remember this?

"SR4759,
I would still like to know: What do you call this bullet?"

.

quote:

Originally posted by ALF:


Because Newton says it is

Is is a principle ! F = m x a

The ratio of that mass to surface area is the determinant of how big the force has to be to attain a certain end velocity !

That is the principle !

Exactly.

And
why with a constant force - changing calibre with projectiles of the same SD ( projectile weight changes)............the higher calibre projectile achieves a higher velocity per unit mass than the lower calibre projectile.....in practice.

similarly
why with a constant force & constant calibre ,changing SD changes velocity inversely proportionate to both SD & mass.

these are all variables we can measure in the acceleration event in practice to identify the efficiency of energy transfer of force relative to SD..........AND per unit barrel length.

In a deceleration event ..........the efficiency of energy transfer is also proportionate to SD.In that case the energy transfer is into the target......AND per unit penetration length.

The fundamental energy transfer dynamic doesn't change going up or going down in energy transfer........AND its proportionate to SD.

In the acceleration phase the SD is constant .
In the deceleration phase the SD is undergoing dynamic change.....and the rate of energy transfer is undergoing dynamic change in proportion to SD.

nobody has found a way to have your cake & eat it too...........without creating energy.

SD has PRACTICAL implications in both the ballistic acceleration event & the ballistic deceleration event.

That Newton was a smart fella.

quote:

That is the principle !

It is one of the principles and, by far, not the most important one.

quote:

Originally posted by Cross L:

quote:

Originally posted by ALF:
Trax:

yes !

The "mistakes" made in the interpretation of the tests are numerous but most probably the greatest error derives from the fact that behaviours are reported that are not tested for.

As I have tried to show over and over it is a two way street.

Only the bullet behaviour is tested for in the simulation, not the target behaviour and even then only certain behaviours not all.

So if there is comment bullet expanding or fragmenting etc etc then that part is ok, the minute there is reference to the amount of trauma done to the paper stack or gelatine or reference to this likely being a better killer than that, as observed by the amount of damage to the target then the test is invalid, no matter how many times over you repeat the test !

It is a systematic error in the methodology employed.

Yes I agree that the amount of damage to the target material would constitute a measure of lethality in living tissue but sadly simulation testing does not test for this..... this is the problem and people do not seem to get this.

The hole you see in gelatine and the hole in paper after shooting is not representative of the amount of damage done in various tissues. This is why basic science in ballistics is so important.

Just to illustrate here is a picture posted from the terminal thread



This is the "trauma" done to the paper.

Simple questions:

1. What caused this damage ? By that I mean by what mode of action did this occur? by the bullet striking the target------

2. Do you see this behaviour in living muscle , or bone or organ tissues? In other words if you shoot your animal do you see this destruction and mass of devitalized tissue ejected from the target ? that doesn't matter--as you have been informed many times it IS possible to correlate data given enough datum points-contrary to your innuendo Michael has never asserted that his medium reacts the same as an animal--just that you can correlate some aspects of the event.

This whole thing to me is amazing because this thread on terminals is so important it has been made a permanent fixture on AR. Not surprised that you are confounded-it isn't that hard to do

So anyone wishing to find out about ballistics who googles Terminal behaviour is going to get this popping up on their screen. They may actually believe that what they see there is how things happen ? Yep because it is exactly as represented and is repeatable

I cannot wait to see some kid at school presenting this for fact when asked to write a term paper on ballistics ! He would get a A-

Still don't get it do you--


SSR

Quote CL
" that doesn't matter--as you have been informed many times it IS possible to correlate data given enough datum points - .......................... - just that you can correlate some aspects of the event. "

Correlations are assumptions in the absence of identification and explanation of a dynamic.

Correlations cannot be relied upon to consistently achieve output relative to input.

Correlations ASSUME an approximate relationship
Correlations PROVE nothing .
Correlations with an R-factor of .95 or better indicate a high likelihood of a real relationship.
Correlations with an R-factor of .7 or better are mathematically regarded as good correlations.( but have a high variance of predicted outcome to actual).

an example I use of the danger with correlations follows

not all that long ago scientists correlated weight gain with potato consumption because there was a correlation between carbohydrate consumption & weight gain .
Dieticians concluded that potato consumption was not good for you & recommended reduced potato consumption to control weight gain.

A little while further down the track scientists discovered there were different energy transfer implications for simple carbohydrates & complex carbohydrates & that weight gain was associated with complex carbohydrates.

The reality was that potato is a simple carbohydrate & is good for you as an excellent source of nutrition & energy, the problem with weight gain was not the consumption of potato , but what you put on it to consume it.

Dieticians had to change their view very smartly.

This is the danger with using correlations in practical life and why a high proportion of humans make mistakes in assuming that because something works in one situation it can be translated directly into another situation.

I commend the body of work done on terminal performance as a body of investigatory experimentation.
Its onerous work & requires effort & dedication.

The conclusions drawn from the body of work establish a very good correlation between product design & effect.
The conclusions drawn between cause & effect however are quite risky.
Physical science actually explains the relationship between construction and effect and the nature of energy transfer that the construction manipulates.

The construction of the product is applied science ( VERY good applied science BTW)...........the construction does not create new science.
The construction will still respond to the resistance it encounters in penetration and react according to the relevant physics.

Some assumptions made, based on the correlation from the body of work, by readers, are risky.

Readers are typically neither scientists nor mathematicians to be able to understand the risks involved in correlations or how to interrogate the assumptions contained in correlations..........to translate results from one situation to another, in assigning cause to effect.

Quote:
" This whole thing to me is amazing because this thread on terminals is so important it has been made a permanent fixture on AR "

A "sticky" in AR , a high hit number in Google, nor a quotation in Wikipedia, make a statement necessarily a scientific fact. The statements made need to be mitigated with respect to their context.

Again,
A great body of experimental work in the Terminal Penetration thread & others of similar nature with other bullet types that can be found in other sources.
The risk for the reader is interpreting cause & effect in translating the results to another situation.
That's actually another correlation.......not the 'as read' correlation.

Damn details keep getting in the way .

quote:

Originally posted by ALF:
Cross L

No my friend the bullet did not do that, it is the energy transfer due to drag experienced by the bullet that did that damage !

The key lies in drag, everything ballistics when looking at intermediate and terminal ballistics come down to this little overlooked inconvenience of surface area A and it's variability.

Big difference, perhaps it is you who do not get it

Round nose bullets would penetrate the same a FN bullets and low and behold there would be no need for your magic bullet at all, you could simply shoot round balls of same caliber and they would do exactly the same.!

So one can have a lower Sd bullet with a lower drag co-efficient,.. that would penetrate better than a higher Sd bullet with higher drag co-efficient .

.

Alf,

If two bullets of the same mass and diamter impact am animal in the same location, at the same velocity but one stops in the animal and the other exits the far side, which will destroy more tissue?

465H&H

.

quote:

Originally posted by ALF:
The bullet that loses the most energy to the target will have the potential of doing the most damage.

I specifically say potential because not all tissue reacts the same to energy , it depends on the mechanical properties of the tissue. ( not all energy transferred translates to damage)

it depends where the energy was shed in the target.

This scenario illustrates then the issue of the dynamic nature of SD.

If both bullets impacted at the same velocity and had the same SD at point of impact, had the same path in the target and one shoots trough and the other stops in target then there has to be a difference between the two bullets and their behaviour. Either one tumbled or deformed or fragmented and this could be by design ie intentional or unintentional.

The classic study showing this was done by Charters and Charters published in the Journal of Trauma in 1976, later then also shown in testing done using "Computer man" which is a computerized simulation model.

Alf,

I was more thinking in the line of a RN solid versus a FN solid. In my experience on elephant heart/lung shots from a caliber such as the 470 Nitro, the RN is more likely to not exit while the FN is more likely to do so. Which then would cause the most trauma?

465H&H

.

quote:

Originally posted by ALF:
...
In the case of paper which classifies as a woven composite and slug of compressed paper forms in front of the penetrating projectile and that in itself is driven as a projectile , the margins of the failure typically way in excess of the diameter of the penetrating projectile. this is exactly how Kevalr works to "catch" a bullet.

So the observation of "massive trauma" is not wrong it is why it happens is at fault.

Muscle and organ tissues does not do this! ....

quote:

Originally posted by ALF:
Do you see this behaviour in living muscle , or bone or organ tissues? In other words if you shoot your animal do you see this destruction and mass of devitalized tissue ejected from the target ?.....

..The hole you see in gelatine and the hole in paper after shooting is not representative of the amount of damage done in various tissues..

What promotional impact would there be without the exaggerated & dramatized effect of artificial simulations?

Wetpack tests remind me of the Colgate simulations .


if one can " pretend this chalk is your tooth" ...... one can also " pretend this stack of wet paper is live game"

quote:

one can also " pretend this stack of wet paper is live game"

You have to test on something otherwise all you do is talk.

In theory, theory and practice are the same.

In practice they are not.

I see no problem with entertaining and educating oneself and others, by test firing projectiles into various forms of artificial test media,
...however there are flaws in some of the interpretations made and conclusions drawn, from the results achieved.

I find this kind of testing more valuable: http://www.youtube.com/watch?v...QU0U&feature=related

quote:

This scenario illustrates then the issue of the dynamic nature of SD.

Which is called something else. Sd cannot be dynamic because it is a static number. It could change to another static number but the starting value is no indication of what the changed value may be. This renders the starting value as useless information that serves only to misinform the uninformed.

quote:

A high SD bullet reaches deeper into the target than a low SD bullet.

There lies the origin of what the uninformed will use. He will now go out and buy the heavier version of two bullets in this belief. The twist of the rifle is fixed and the heavier bullet must be more prone to instability when it transitions from flight to tissue. This will reduce its terminal performance compared to the shorter and faster bullet. Not every time, but enough times to make the shorter bullet the better choice.

When the uninformed seeks to be better informed it is commendable. When the uninformed is misled with useless information, that is despicable.

Printing tables of sd values for bullets or giving the value on the box, is a waste of time and serves no purpose.

quote:

The twist of the rifle is fixed and the heavier bullet must be more prone to instability when it transitions from flight to tissue.

This has not been my observation. It was my belief at one time but not anymore. The very long 175gr 7mm FMJ RN Mauser bullet was known to exit an elephant's skull with a frontal brain shot. That's a lot of solid bone! I've seen how deep a 55gr SP 224 bullet stabilized with a 1-in-16 twist hornet barrel can penetrate nose first into soft and uneven flesh. Also in test medium. They just don't tumble.

60gr on the left, 55gr on the right. 1-in-16 in a hornet.



I've fired up 262.5gr cast from a 303 Brit and those too travelled nose first in test medium. They did sometimes bend and turn in the medium so this would give some support to the heavier for calibre bullets being less stable in flesh assertion.

Here are two 230gr bullets fired at different velocity.

No tipping.

Here's one that bent. It was quite slow and its penetration rather deep. Way deeper than a faster bullet.


This one came to rest sideways.

This is what they look like when fired faster.

quote:

This has not been my observation. It was my belief at one time but not anymore.

Your photos and writing contradicts that statement.

quote:

They did sometimes bend and turn in the medium so this would give some support to the heavier for calibre bullets being less stable in flesh assertion.

The photographs you posted raises the questions: In the first photo it is clear that the bullet was travelling sideways at some stage to cause the damage indicated by the arrows. Also, how does a bullet bend if it does not have substantial force applied at an oblique angle? In the second photo, the damage to which the arrow points could only have happened if the bullet was travelling backwards. If a bullet is travelling backwards, is it not tumbling?




In any case, I did not equate instability during penetration with long bullets. Stability in the target is governed by other factors. I said that stability in the transition from flight to tissue is compromised. They are two different things, although transitional ballistics will affect terminal ballistics.

quote:

Originally posted by Gerard:

quote:

This scenario illustrates then the issue of the dynamic nature of SD.

Which is called something else. Sd cannot be dynamic because it is a static number. It could change to another static number but the starting value is no indication of what the changed value may be. This renders the starting value as useless information that serves only to misinform the uninformed.

quote:

A high SD bullet reaches deeper into the target than a low SD bullet.

There lies the origin of what the uninformed will use. He will now go out and buy the heavier version of two bullets in this belief. The twist of the rifle is fixed and the heavier bullet must be more prone to instability when it transitions from flight to tissue. This will reduce its terminal performance compared to the shorter and faster bullet. Not every time, but enough times to make the shorter bullet the better choice.

quote:

Printing tables of sd values for bullets or giving the value on the box, is a waste of time and serves no purpose.

It appears by this definition of a static nature that velocity, mass, momentum, bullet length etc. are also static in nature. Does this then also render the starting values of these parameters useless information because they change as bullet flight and penetration occurs? Do they also misinform the public? Why id SD held to a different standard then the others?

465H&H

.

quote:

Originally posted by Gerard:

quote:

This has not been my observation. It was my belief at one time but not anymore.

Your photos and writing contradicts that statement.

quote:

They did sometimes bend and turn in the medium so this would give some support to the heavier for calibre bullets being less stable in flesh assertion.

The photographs you posted raises the questions: In the first photo it is clear that the bullet was travelling sideways at some stage to cause the damage indicated by the arrows. Also, how does a bullet bend if it does not have substantial force applied at an oblique angle? In the second photo, the damage to which the arrow points could only have happened if the bullet was travelling backwards. If a bullet is travelling backwards, is it not tumbling?




In any case, I did not equate instability during penetration with long bullets. Stability in the target is governed by other factors. I said that stability in the transition from flight to tissue is compromised. They are two different things, although transitional ballistics will affect terminal ballistics.

Fair comments. I was expecting your challenge - very astute! OK to answer you, the first bullet - the bent one - suffered those trailing edge damages on throat entry and they are on the full circumference of the trailing edge. It's a problem I'm having to solve which is in the form of the next photo with the rebate. That ding you arrowed was actually caused by the nose pealing around. I prized it off the base to have a look. There is another one just next to it. Those bullets really do not tumble in the media I use. This one illustrates that point better, I think.



The patch has not been disturbed and is actually covered in one spot by the folding over nose. It has been washed in water. Sometimes they carry bits of cloth that get sucked in behind the bullet as well as bits of the rubber grindings of the catch medium.

I'm sure we are not in disagreement, it's just that there are so many variables and scenarios and the difficulty of expressing stuff in writing so others can fully understand. I admit to not always getting what you are saying - my own fault of course. Anyway, soft lead bullets do not predict how a monolithic copper bullet will behave. Their SD's and velocities are different. By SD I mean that for similar lengths the copper bullet would be lighter, being less dense and a more streamlined shape. Saying that I realise the SD is actually a poor reference because it ignores the physical shape of the bullet.

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Why id SD held to a different standard then the others?

Mass and bullet length are static, velocity and momentum are not. So there are no differing standards. It boils down to what is usable and what is misinformation. I used sd yesterday in a calculation of a parameter of a new bullet that I am working on but what is the use of sd to the guy that does not even know how to properly set up a sizer die? The use of sd as a measure of penetration depth is nonsense because uninformed reloaders say 'I am using this (non bonded core, hollow point, match) bullet with the higher sd because it penetrates better than that (bonded core, thick jacketed, partitioned) bullet'.

In the context of equating penetration depth to sd, as a single parameter, it is wrong. That is all I have said all along and writing reams of paper about where sd is used in calculation does not change that. Everything said about the role of sd may be right, but more sd does not translate into deeper penetration. There are always more important factors and no single factor works in isolation.

It has long been time for the myth to die.

Alf,

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The concept of more vs less stable?

That is why we work with the concept of stability factor. An object is stable or not but, the stability factor for a stable/unstable object can vary.

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I honestly do not understand why this issue of SD being dynamic and not static is such an issue ?

Because sd is not dynamic. How can sd be dynamic? It is the ratio of the weight to the square area exposed to the direction of motion. One object can have different sd values depending on the point of view. It can change but it cannot be dynamic.

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Once unity is attained between the overturning moment and the gyroscopic moment a state of static stability is reached.

Thank you! If an argument could be made (and it cannot) these values could be construed as 'dynamic'.

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there is no twist fast enough that can stabilize a projectile in a target with the density of muscle !

See the quote below. This is another misconception that is doing the rounds: That twist can determine stability within the target.

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Stability in the target is governed by other factors. I said that stability in the transition from flight to tissue is compromised. They are two different things, although transitional ballistics will affect terminal ballistics.

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In the context of equating penetration depth to sd, as a single parameter, it is wrong. That is all I have said all along and writing reams of paper about where sd is used in calculation does not change that. Everything said about the role of sd may be right, but more sd does not translate into deeper penetration. There are always more important factors and no single factor works in isolation.

We are indeed in agreement. But we do have totally different perspectives, perhaps from the opposite ends of the spectrum. In isolation our perspectives don't mean much to each other but brought together in the bigger picture perhaps they expand our understanding. I'm afraid I have no way of exploring your area and you have need to explore mine. But your area is interesting to me just the same.