quote:

Originally posted by ASS_CLOWN:
Yes Norbert, please straighten Henry out. "sectional density" aint cross sectional area. It ain't density either since the "mass" term is actually a weight.

grains divided by 7000 = weight NOT mass...

The distinction between weight and mass is irrelevant to this problem.

Since gravitational acceleration is constant anywhere these bullets actually get used, the conversion 2.2 lb = 1 kg applies. We are again arguing about a unit conversion. It confuses us some, because we were taught that pounds is weight and kilograms is mass and there's a factor of 9.8 in there somewhere. Since that factor of 9.8 is a constant, everywhere, all we've done is measured mass in a different unit.

Have you ever weighed a bullet on a digital powder scale? Was it one of those ones that let you use grains or grams? The exact same physical measurement is being made, and units are being converted by the scale by simple multiplication. Your powder scale reads 19.48 grams when a 300 grain bullet is sitting on the pan. That or it needs calibrating.

Did your digital powder scale cost you less than $1000 (US)? Guess what? Even if the readout is in grams, you were measuring weight, not mass. Those cheap digital powder scales use a strain guage to measure an elastic deformation. They are a spring scale, in effect, and they measure weight in "grams". Does it matter? Nope. Not at all.

Take the same bullet to your drug dealer and have him weigh it on a triple beam balance. His triple beam will read 19.48 grams, just like your digital powder scale did. Why did the two measurements agree, even though your drug dealer has the proper instrument and you don't? Gravitational acceleration is the same at his house as it is at yours. It's the same where you hunt too.

Now, imagine you and your drug dealer could go for a ride to the moon. You can smoke lots of pot on the way there and eat a whole box of Cheezits too. Okay, I hope you remembered to bring that 300 grain bullet with you. Weigh it on your drug dealer's triple beam. Yep, 19.48 grams, just like on good old Earth. Now try your digital scale, set to grams. Aha! You thought you were measuring mass, but now why does your bullet "weigh" only 3.32 grams? Did it get smaller? Did you eat some of it when you ran out of Cheezits? No! Gravity got smaller. Your drug dealer is measuring mass with his triple beam balance (regarless if he's selling you ounces or dime bags), and your wonderful digital scale, calibrated in grams, is measuring weight.

QED

H. C.

Please forgive me, all of you techno-wonks out there, both those who elucidate, and those who obfuscate, but . . . given the title of this thread, I have been wanting to say for some time:

"Yes, it do."

quote:

Originally posted by mrlexma:
Please forgive me, all of you techno-wonks out there, both those who elucidate, and those who obfuscate, but . . . given the title of this thread, I have been wanting to say for some time:

"Yes, it do."

Damn, you are good!

mrlexma,

That sums it up well!

Ron,

Definition of "momentum density". Well I suggest a search for "shear stress" . I am confident you will find lots of references to "shear stress". The difference between "momentum density" and "shear stress" if you integrate "shear stress" with respect to time you will get "momentum density".

When can we start discussing something with some "meat on it's bones"? Lets talk penetration characteristics of jacketed soft point bullets!!!! Come on gentlemen, I am very confident it will be great fun!

Good night,
ASS_CLOWN

AC,
That subject is intractable to my small mind. I yield to your superior intellect. I know my limitations.

I like the bit where Norbert said something along the lines of-

If the slower bullet penterates better, will not the faster bullet then start 'penetrating better' once it has reached that lower velocity too?

You would assume at the very least it would at least have the 'small headstart of penetrating a bit' before reaching that lower velocity as well.

I notice the other camp neglected to address this point and slipped into general shitslinging instead.

Karl

to all.

RIP,
I do not know why Alf will not admit to the fact that, if the same bullet is run faster and penetrates deeper it is as a result of additional momentum not Sd. I do not think that acceptance of Sd in ballistics is an option for me. The correct bullet for a given twist and calibre is the correct length of bullet if terminal performance is the primary concern. If the terminal performance with the correct length of bullet will not do the job at hand, one is better served by another calibre that will. The coup de grace for Sd is the discovery that it results in square bullets. Now I must apologise to Chris as this is clearly the source of the square cylinders he will be reporting on in his next article. I am humbled, I did not know. (It does lend credence to an article I wrote titled "Sd - A practical Joke?")

Norbert,
I apologise if you are offended by my comments. Your statement that stagnation pressure has nothing to do with penetration regarding solids is of course correct. It was not clear to me, as well as to Will, that expanding bullets were excluded from your comment. My comment was in the context of expanding bullets where stagnation pressure does play a significant role in expansion and hence penetration.

Regarding Sd, it is my position that Sd is no indicator of likely penetration. It has to be linked to movement and at that instant the correct term is no longer Sd. Whatever it is called, seems debatable, but it is not Sd. Velocity can substitute for bullet weight and is in many cases the preferred way towards good penetration. Think supercavitation and the reduced area exposed to the direction of movement of a cylinder as opposed to a cone or half sphere. We routinely match the momentum values of heavier bullets with light ones within the same cartridge and it is even more easily done within similar calibers. Think 7x57, 7x64, 7mm RM and so on.

My reference to selling bullets was a dig at Will which is why I added the little winking face to it. I did find your bullets for sale on the Reichenberger site, have you stopped that then?

HenryC470,
When bullets become too short, practical limitations such as case and freebore dimensions and BC exclude them from consideration and the question becomes so hypothetical that it warrants no inclusion in a discussion. You are absolutely right about the goat.

Alf
The question of momentum density is a dilemma. Norbert used it and, if I recall correctly, Chris as well. In haste I repeated it in a reply to Norbert, when what I was thinking was Mo/XSA. Momentum Density is is the amount of momentum per unit volume and is expressed as kilograms per second per meter squared. It is most commonly used in the field of electromagnetics and is of use to automotive engineers in the area of suspension design. Mass times velocity divided by cross sectional area is of course Mo/XSA which is what we work with to find approximate comparisons between bullets.

mrlexma,
No, it does not with expanding bullets. Only with non-deforming solids sufficiently stabilised for linear penetration.

Chris, you exaggerate and blow small things up way out of context. It is quite entertaining when you get bent out of shape like that, even to the extent that you throw in a fear factor and psychological analysis for dramatic effect. Calm down, this is a technical discussion. You keep repeating yourself and thereby force the rest of us to do the same. Here is a new perspective.

In your test, momentum and momentum/XSA indeed correlated well with the penetration. Much better than Sd. In fact, Mo/XSA correlates so closely to penetration in your test (by a factor of exactly 11.8 for all three bullets), that one could probably do very accurate extrapolations from it. So, substituting your cut down Barnes bullets with solid cylinders to remove the variable of differing expansion, we can make the following prediction.

You take your fave 175gr cylinder and shoot it from an old 7x57 96 Mauser with a 20" barrel at 2200 fps. I am told that this is your preferred hunting velocity. We ask RIP to use his 7-08 and he shoots the 142gr cylinder at 2712fps. Alf kindly uses his 7mm STW and shoots the 108gr cylinder at 3565fps. In your article the penetration correlated with the Mo/XSA values of the three bullets in perfectly linear manner by a factor of 11.8. Using this factor, we predict a penetration depth of 57.76cm for all three bullets. This proves by your own method that Sd does not indicate the likely performance of a bullet.

Bullet / Speed / Momentum / Mo/XSA / Penetration / Sd
175 ---- 2200 ----- 55.00 ------682 ------ 57.76 ---- 0.310
142 ---- 2712 ----- 55.00 ------682 ------ 57.76 ---- 0.252
108 ---- 3565 ----- 55.00 ----- 682 ------ 57.76 ---- 0.191

Gerard,
Thanks. I'll bet Henry will listen to you. Sectional density is calculated using square bullets. It is proportional to reality, but it ain't real.

My searches have also turned up only a momentum density related to electromagnetics and particle physics, more akin to physical chemistry and quantum physics, where I do not want to go. I did ace physical chemistry 30 years ago, but they graded on the curve, 65% was an A.

Norbert did say that MV/XSA was the basis for penetration in all the military equations of the past.

It seems "momentum density" is a corruption of terminology by association with sectional density. But MV/XSA does not utilize square bullets! MV/XSA is real.

I propose to call MV/XSA by a new name. I surrender BAM (formerly my Bullet Area Momentum) for use in this regard.

BAM = MV/[(pi)x(d/2)^2] = MV/(pie are squared)

BAM is a useful term now.

Also, thanks for pointing out the need to own 60 differnt rifles to make use of equal momentum loads within the various calibers you offer, at safe pressures.

I hope no one is offended by this but it is the truth.

Momentum Density: is Momentum per unit volume. This has exactly the same units as the third derative of displacement. Better know as Jerk

.

RIP:
I don´t understand all this dicussions on SD or M/XSA. It is obvious that you and others (and me too) are right, that SD is somewhat arbritrary and not a correct physical figure.
But: Every loading manual produced by every modern powder / bullet company over the last 30 to 40 years all refer to this "non entity". So I sometimes was simplifying comments and I should write: Sectional density has to do a lot with penetration. Multiplying with velocity it gives a figure proportional to momentum density, the basic number for all penetration research. It is still a good guidance for selecting bullets for wanted purposes. To use D^2 instead of
(pi)x(d/2)^2 makes only a difference of 30% in the denominator, but we are looking for the trendlines and not number crunching.

The force, which is needed to penetrate, is F=d(m*v)/dt.
That means, the force equals the change in momentum with time. It is needed to overcome shear stress in solid material or the flow resistance in aqueous media, friction and so on.
Now it is very important how large the area of the target is, on which this force is acting. So we get the momentum density,
Mass times velocity divided by cross sectional area and is of course M*V/XSA. In german it is called Impulsdichte. I have simplified this thoughts too for better understanding and a guideline for us hobby ballisticians. It can also simplified for bullets (a steady mass is acting), the military use it more complex for e.g. research on shaped charges, where a streaming volume has to be taken into account. Momentum and Impuls in higher grade physics are very complicated and used for many different phenomenons.

Because all this is so simple, why introducing a new term and confusing hunters more? Or should we use square bullets? an interesting idea.

Gerard:
That you say: "Regarding Sd, it is my position that Sd is no indicator of likely penetration." I can absolutely not understand
Velocity can not substitute for bullet weight in all instances, I gave an example above

Reichenberg has the SuperPenetrator bulltes on sale, but I have no commercial interest in this business.

I was reading this thread hoping it would help me decide if i should take out the 505 gibbs or the 338 Lapua today but now it is raining, so i guess it does not matter.

Sectional density is what we call in engineering a FOM (Figure Of Merit) and are made up all the time as a convient way to compare "value" with the same contributing scale variables and is usually a relative comparsion and not an absolute.

For example:

Sectional Density = breast size * hip size/waist size

so rather than saying 38-24-36, i say her SD=57 and when i hear a SD of 64, i fall out of my chair. In an absolute sense, i do not know what 64 means, but it must be good.

rgrds,

steve

quote:

BTW off topic: Why do the military try to enhance velocity for maximum penetration? Reportedly speed up to 3000 m/s may go through an Abram M1 like butter.

As was discovered during WWII, if the impact of the bullet is at a higher speed than the speed of sound (a) inside the bullet and (b) inside the target, then the physics of the impact are the same as liquid hitting liquid, allowing very deep penetration. The speed of sound inside steel is above 5000 fps. Some weapons (bazooka) use a "shaped charge" that accelerates the nose of the projectile after it hits. Liquid hitting liquid at 5000 fps makes an impressive hole. Unfortunately, such is not practical in a hunting rifle. If it were, it would not matter if the bullet were solid, soft nose, or whatever.

Norbert,
Thanks. I left the "hard" sciences behind for medical school, 27 years ago.

Of course I am not proposing use of square bullets to make the sectional density a reality, nor am I seriously proposing the use of BAM as nomenclature for momentum density.
Just a joke, in fun.

I have come across the term "jerk" before, but that is not the same as we are interested in here. And I certainly don't mean to come across as a "jerk" myself.

I agree that Gerard should not be so phobic about use of sectional density, as it is directly proportinal to reality, and a useful simplification that we are stuck with from ancient history.

Alf,
Did you use a flat nosed solid in that 7mmSTW that failed to penetrate one critter that the 7x57 perforated three of?

No you did not, and the frangible bullet blew up in the gemsbok or wildebeest or whatever.

I think Gerard is just yanking our chains with this sectional density thing because Chris Bekker leans on it so hard as a crutch. Gerard is just trying to pull the prop out from under Chris Bekker.

Wrestle with pigs and you get dirty. Let him go Gerard, he is not in your league.

All that matters is momentum and pi are squared.
BAM!

quote:

Originally posted by steve505:

For example:

Sectional Density = breast size * hip size/waist size

so rather than saying 38-24-36, i say her SD=57 and when i hear a SD of 64, i fall out of my chair. In an absolute sense, i do not know what 64 means, but it must be good.

rgrds,

steve

Unless of course SD=64 was reached by the measurements 24-24-64

Now interesting to note that, if you were to use cm's as your unit of measure the number would be entirely different. Likewise every SD number I have ever seen was calculated using (Lbs/in^2) yet these units are not listed as a suffix to SD. Hence the erroneous assumption by many that SD is a unitless figure. But just because we now know what units the figure is derived from does not mean that it's values may be plugged willy nilly into any equation of the day. SD was never intended to be used that way.

In my book the Term FOM is absolutely correct.

quote:

Originally posted by TheBigGuy:

quote:

Originally posted by steve505:

For example:

Sectional Density = breast size * hip size/waist size

so rather than saying 38-24-36, i say her SD=57 and when i hear a SD of 64, i fall out of my chair. In an absolute sense, i do not know what 64 means, but it must be good.

rgrds,

steve

Unless of course SD=64 was reached by the measurements 24-24-64

Now interesting to note that, if you were to use cm's as your unit of measure the number would be entirely different. Likewise every SD number I have ever seen was calculated using (Lbs/in^2) yet these units are not listed as a suffix to SD. Hence the erroneous assumption by many that SD is a unitless figure. But just because we now know what units the figure is derived from does not mean that it's values may be plugged willy nilly into any equation of the day. SD was never intended to be used that way.

In my book the Term FOM is absolutely correct.

Some still don't get it.
Units of sectional density are pounds divided by imaginary square inches of fantasy square bullets. So sectional density has no real units.

Sectional density is just a ratio. And it is a ratio of apples to oranges. But it is indeed an FOM.

.

Alf, I have been living with a 7x57 Mauser for a long time and have owned many others. I truly regret selling a couple of them and at the moment I have two. In the last 25 years, I have accumulated the bits to build myself a 7mm RM three times. Nice choice bits. And three times I sold off the parts. I do not feel the need for anything more powerful in the mid range.

After all the backwards and forwards on this thread, I cannot remember who said what but from my side some clarification is in order.

When comparing/predicting terminal performance:
Sd is of no use.
Speed alone is of no use.
Momentum is only of use for comparison of same caliber bullets. (XSA becomes a constant and can be discarded)
Mo/XSA is used for comparison of dissimilar caliber bullets.
Very little is of use for comparing dissimilar calibre bullets that also differ in construction, other than .

Momentum or Mo/XSA indicates likely penetration.
Ke indicates the probable wound channel volume.

The important bits are:
Terminal bullet condition (shape).
Retained speed.
Uniformity.
Sufficient force to shoot through.

My first choice in a bullet for any caliber for normal hunting will be the bullet that is correctly stabilised with a gyroscopic stability factor between 1.4 and 1.6. It must expand reliably from 2000 fps and must not break up, ever. Go outside this envelope and you are shooting second best.

Finally, we are making progress here. Some quotes that gladden my heart:

"Sectional density is calculated using square bullets. It is proportional to reality, but it ain't real. I fully concur SD is not mathematically true and correct. I cannot now simply rely on that admittedly mathematically challeneged SD value alone. SD is somewhat arbritrary and not a correct physical figure. Sectional Density = breast size * hip size/waist size. I think Gerard is just yanking our chains with this sectional density thing because Chris Bekker leans on it so hard as a crutch."


When a popular but incorrect concept is challenged, there is always great resistance to it initially. Tedious as these discussion may have been to some, I confess to having learned a great deal. Some concepts have been sharpened up and some fun was had.

Maybe if the the big manufacturers see we are all a bit sharper, they will stop talking about Sd and start concentrating on more useful information. The only reason why they supply Sd numbers is because the customer demands it and it is easy to supply.

How about a label that says. "This bullet can be applied at a Mo/XSA value of A to B and be expected to retain a minimum of x% weight."

quote:

Originally posted by ASS_CLOWN:
Therefore, I recommend a new more interesting discussion. The penetration characteristics of the jacketed soft pointed expanding bullet. How is everyone at solving higher order differential equations? I guarantee you all a discussion on expanding soft point's penetration will separate the "men from the boys"!
ASS_CLOWN

Granted sectional density is a comparison value at best......... BUT

Given a constant frontal area and coefficient of form and all else equal; more weight/mass behind this frontal area will give more penetration in an EQUAL medium. More velocity will do the same thing! These things don't happen in the real world unfortuately.

BUT WE DON'T LIVE IN THIS WORLD OF PERFECT BRASS CYLINDERS!!

And most of us could care less about their ballistic or terminal performance.

The question was about more velocity giving more penetration with game bullets Yea or ney?

IF you fellows are going to prove or even get more than an estimate of what happens don't argue about the definition of S.D. Get EVERYTHING INTO THE EQUATION! We need the frontal area and something for its coefficient of form value as well. Even a fast flying cylinder can have this change due to "rounding off" of the square edges.....THEN WE NEED TIME FACTORED IN! A mushroom just doesn't instantly happen at a certain depth(as certain writings have used for calculations) it happens over time....... Milliseconds yes, and a CONSTANTLY CHANGING VARIABLE as well. The form (frontal area/coefficient of form) also is a CONSTANTLY CHANGING VARIABLE OVER TIME.

When everything is in the equation then MAYBE mathmatically one can show why a faster bullet may penetrate less than the same bullet going slower even while keeping 100% of its integrity and sometimes ending up the very same diameter!.

The reason is it has more frontal area SOONER in milliseconds as well as depth. AND IT WON'T SLOW DOWN AND THEN BE COMPARIBLE TO A SLOWER VELOCITY STARTING AT A GIVEN DEPTH OF PENETRATION EITHER (as was mentioned) Sorry, doesn't work that way!

So I'm with ASS_CLOWN'S quote above! Let's see the equation with TIME and the rest of the millisecond changing variables factored in!

Then know it won't relate accurately to game with another ever changing variable of density changes inside our animal as well.

One can learn just as much with old phonebooks and plan H2O I'm afraid...........

BigRx

quote:

Originally posted by RIP:
Gerard,
Thanks. I'll bet Henry will listen to you. Sectional density is calculated using square bullets...

I will gladly listen to Gerard, but if he tells me that sectional density is calculated using square bullets...

Let me acknowledge that I am quibbling about grammar, semantics, and algebra here. Saying that this calculation is performed using square bullets is a lot like saying that sheep are counted by sticking one finger up, then another, then another,... one, two, three, ... until you run out of sheep. I am sure some sheep are counted that way. If it helps get to the right answer, that's fine. Other sheep are counted by putting little tick marks on a sheet, with every fifth mark crossing the preceding four.

Yes, strictly speaking, sometimes, by some people, sectional density is calculated by imaginig square bullets. Heck, it gives the right answer. Why not? Other people write down the numbers on a sheet of paper, do the sqaring and long division, and they never use, invoke, dream about, or rely upon a square bullet.

In any case, a real number (in every sense) is generated, and if everyone calculates sectional density that way, everyone has a useful numerical parameter to compare bullets with. With attention to details like speed, bullet construction, and target composition, that numerical paramet we call sectional density does give a basis on which to predict penetration.

I will not accuse you, RIP, of using square bullets as a red herring. There are those who would steer people away from the intuitively reasonable and experimentally verified result that longer, heavier bullets penetrate further (other things being equal) for whatever reasons they have. I don't think you're one of them.

Again, I'm arguing grammar, semantics, and algebra. There are a lot of topics about which I am truly ignorant, but these are not among them.

H. C.

quote:

Originally posted by ALF:

Then I entered the word "Momentum density" and funny nothing, not a single reference other that this tread.

Can someone please point me to a reference work or physics citation where I can learn about this?

Alf

Out off topic, but some comments on stupid Google:
Google refers only to articles published in the web. But military small arms research is not published there and of minor interest.
When I introduced the concept of supercavitation to terminal ballistic in 1998, there was no reference in Google. Not before 2001 was an article in the "Scientific American". But in the 19th century german military researchers were already close to this phenomenon. You may find references under the synonym "Kopfringgeschoss". And now Americans developed high speed torpedos using supercavitation.
Shaped charges for maximun momentum density were conceptual described in 1888 by an french physicist Munroe, but came first to application 1940 by the germans, destroying Fort Eben-Emael in a rush.
It is difficult to find citations, but one I can give here: Rheinmetall, Waffentechnisches Taschenbuch, Ratingen 1995, page 55 ff.

But let´s stop this thread and go to more african hunting topics, not extension in higher physics.

.

Another interesting thing about the thread.

I notice some in the debate are pulling their intellectual punches so as not to upset certain parties.

I thought it was the providers age old lot to pull their punches publicly, so as not to upset potential customers.

Karl.

Karl,
Henry isn't punching at all. He is digging and won't put down the shovel. He is digging a nice square hole for himself.

TheBigGuy gave us the definition of momentum density = momentum per volume = jerk. Either the SI units or lbs.ft. per cubic inch, are still units of jerk. I beleive AC has mentioned that fact here long ago but it is not applicable here.

The kind of momentum density that Norbert is talking about is lbs.ft. per square inch or whatever SI units. This does seem arbitrary to define as "momentum density" when "moment pressure" makes more sense.

Lbs.ft. per square inch would seem to be units of "pierce" or units of "penetration."

Mo/XSA is a penetration index all by itself?

And, I suggest that BigRX and AC have there own thread dealing with jacketed bullet penetration under miscellaneous topics. Warning: Intractable.

I would rather stick with copper cylinders to keep things simple, and I will accept supercavitation as a fact too.

.

Regardless of whether supercavitation is fact or not, isn't it irrelevant for elephant skulls? Only the brain would be subject to creation of a vapor bubble around the bullet; the bone would not.

In that event, would there be any difference in the performance of round nose compared to flat nosed solids, if the medium is BONE ONLY?

quote:

Sectional density is what we call in engineering a FOM (Figure Of Merit) and are made up all the time as a convient way to compare "value" with the same contributing scale variables and is usually a relative comparsion and not an absolute.

Steve,

I was beginning to wonder when someone would put it in accurate perspective. SD is no different than the handy little comparative number called "relative brightness" the optics industry came up with a while back for rifle scopes.

Below from my book when discussing this in regards to scopes. -TONY

"It’s nothing more than the square of the exit pupil size. In other words, a scope with a 5mm exit pupil will have a relative brightness of 25 (5x5). A 4mm exit pupil would be 16 (4x4). For the non-technical folks, it offers a comparison aspect, but the exit pupil size already tells you which one is brighter."

OW,
When we agree that sectional density is directly proportional to reality, we agree that it is an FOM, which puts a name to the agreement, just like your relative brightness example, which also compares square holes to round holes. (Get it yet, Henry?)

Alf and 500groans,
True and true. If supercavitation can be created in any of the fluid portions of the bullet track, it will. In any of the bony/solid portions, the flat nose will punch a better hole and the bullet will be less subject to deflection from the desired straight line.

I shot one of Gerards .416/380gr FN bullets at 2509 fps MV dead center through the trunk of an umbrella thorn acacia at 100 yards paced distance, checking zero off the hood of the bakkie. It was 16" thick.

25 yards beyond the first tree, the FN struck a second umbrella thorn tree of 12" trunk slightly off center. It continued to follow the same laser straight line and went out the backside of that tree too and on into the caroo.

That is over 2 feet of dense live wood and sap. I do not think there was any super cavitation there, but copper cylinders with truncated cone large flat noses seem to penetrate well, and straight.

Just another anecdote.

Alf quote:
>>I would like to know how firing a FN bullet causes supercavitation through a compacted bale of wet hay, cause that is what happens when your bullet passes from "stem to stern" in a grass, twig and leaf eating animal !<<

There is no "scientific" reference, but you can easily see the effect of stabilisation and of straight line penetration, when shooting through water containers. Every 15 cm the cavitation bubble is stripped off and newly generated up to several meters in total. Shooting in animals of course is very complicated, but this stabilisation effect can be observed with body shots and aqueous tissue. In bone is no supercavitation, but after passing bone and other low water containing tissue the cavitation is again build up.
You can only carry out modelling experiments. No one would pay for X-ray shadowgraphs a bullet passing from stem to stern.

quote:

Originally posted by 500grains:
Regardless of whether supercavitation is fact or not, isn't it irrelevant for elephant skulls? Only the brain would be subject to creation of a vapor bubble around the bullet; the bone would not.

In that event, would there be any difference in the performance of round nose compared to flat nosed solids, if the medium is BONE ONLY?

There is a difference. In pure bone my SuperPenetrator design would show about 10 % less penetration, but in reality the ele skull has so much water content, that the SP bullet penetrates deeper than a RN. I examined many, many bullet paths in ele skuls. It is said, that esp. in ele cows the honeycomb structure is filled with liquid.

I believe! Where supercavitation can happen it will!

TheBigGuy, BigRx, and AC ... hmmm?

.

Alf,
Penetration in tissue (including bone) is very much dependent on the shape that is presented to the direction of movement. The larger the surface area, the higher the resistence to penetration. In the metalworking industry this is easily demonstrated by using a coining die with a flat face to effortlessly punch a coin shaped form from a sheet of material or alternatively a rounded die which will simply deform the metal, forming a pocket.

When it comes to supercavitation, I have relied on Norbert's opinion to explain what is going on. I have only the practical observation of shooting animals with different shapes to guide my opinion without being able to explain why or if supercavitation occurs.

Two examples that come to mind that defy "normal" bullet behaviour are:

Shooting a blesbuck (200lbs) in the chest and finding a caliber size exit hole in the last vertebra of the spine. The bullet was a 40gr HV at MV 4400fps and the distance just over 200m. That amounts to 40" of meat, bone, assorted organs, stomach contents and so on.

The other is a frontal brain shot on a lone bull elephant taken in self defense with the bullet entering centrally on the head at an upward angle. The shot was taken at a very late stage of the charge. The angle was steep enough to only clip the top edge of the brain. The bullet exited the rear of the skull and when it encountered the skin of the neck, turned downwards and was found a small distance down the neck. The man used his 300WM with a 160gr HV at 3300fps.

We know that in both cases the bullet would have shed the petals resulting in a cylinder shape, although only the 160gr bullet was recovered to prove it.

We have many such reports from hunters who will attest to the abnormally deep penetration from cylinder shaped bullets, be it FN or HV with shed petals.

What the exact mechanism is, is a mystery to me and I listen and learn.

Alf and Gerard,
That is way too much for my small mind to deal with tonight. I had better sleep on it. Thank you, and good night ... Now if only I could control this nervous tic I have developed since page three of this thread started ...

.

Alf:

You are argumentative for its own sake. Your comments are full of errors or misunderstanding what really is said about bullets stabilisation by supercavitation and therefore preserving its twist. Not the supercavitation itself, but the possibility to keep the gyroscopic stabilisation is the reason for the straight line penetration. All your remarks on asymmetrie of cavitation are not applicable here and splitting hairs. If your thoughts about pressure equilibrium would be right, no aircraft would take off. And no one said, that in bone or dense tissue supercavitation would occur. We don´t need pure water, in any tissue, where the water content is forced to build up a flow pattern, Bernoulli´s law comes into application and cavitation must occur.

quote>>Another phenomeon of progression of a supersonic velocity projectile within a supercavitaion bubble is that the path is not linear, but curved<< Rifle bullets in animals are not supersonic "the gun sight calculates where it has to fire under the mine" is to correct it for optical effects.

quote>>My feeling is that monometal solids of reasonable shape and mass have rewritten the rules of penetration and that it is not due to any newfound phenomenon but simply cause they tend not to deform in the target.<<
This statement is totally wrong. The supercavitation is not a new found phenomenon. As I wrote above, end of 19th century resembling phenomena were studied. BTW, before argueing, you should read carefully what you are fighting against. No modern solids deform, but different construction show very different penetration caused by different degrees of stabilisation.

But if you absolutely do not like the supercavitation, you may call the effect of extraordinary stabilisation of the new SuperP or FN design caused by the Holy Ghost of Manitu. It doesn´t matter, essential is to use this bullets.

BTW, I performed experiments, which confirm the concept of stabilisation by keeping the gyroscopic stabilisation in a supercavition bubble:
Same bullets shot into my water containers test array without gyroscopic stabilisation (barrels with no rifling) tumbled immediatly and veered off course.
Bullets design with lesser ability to build up stable supercavitation (hemispherical RN) show lesser penetration and greater tendency for veering off.
Bullets shot into containers with liquid of high vapor pressure: also no stable penetration and severe tumbling because there is no tendency for cavitation.



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Alf,
Glad you have researched and expounded upon this so well.
Your elephant anatomy and minimization of supercavitation sounds spot on there.

Maybe it is just the normal temporary cavitation that any high velocity projectile produces in wounding, that the flat nosed projectiles are better at producing.

Supercavitation in water, and "better-cavitation" in game, with less deflection and less tumbling than with the round nose "solids" is how I see it, and have seen it in my limited experience.

As for the softs and frangible bullets, I don't even want to go there!

Jack Carter knew the flat nosed solid was better when he designed the Trophy Bonded Sledge Hammer.

John Buhmiller new the flat nosed solid was better when he turned his bullets around and shot their flat bases as the leading surface of the bullet, back in the 1950's and 60's.

I don't care to get anymore technical than this. So I am out of here before I get another nervous tic started up.

quote:

Originally posted by ALF:
So in that I cannot see how you would even in theory get a cavitatiiong projectile to work?

Why do you stick on shots on ele skulls only? I never said, that in bone or airfilled cavities supercavitation occurs. But as RIP says, >>Supercavitation in water, and "better-cavitation" in game, with less deflection and less tumbling than with the round nose "solids" is how I see it, and have seen it in my limited experience.<<

But in addition I made the observation, that frontal ele shots results in deeper penetration with the superc. bullets, apparently there is sufficent aqueous tissue on the way. (trunk muscles, brain, tissue in the neck, sometimes reportedly honeycomb is filled with liquid; we don´t need water filled vessels, any normal aqueous tissue will supply enough water vapour for supercavitation.) See images in the other topic from 500grains.

And now I am with RIP and:
I don't care to get anymore technical than this. So I am out of here before I get another nervous tic started up.