quote:

The formula for the distance it takes a spinning Projectile to become unstable can be found in Munks formula

quote:

Originally posted by boom stick:
So faster twist at same velocity penetrated farther and straighter

Hmmmmm...

Faster velocity same 1:12 twist farther and straighter

Hmmmm...

quote:

Originally posted by Gerard:

quote:

The formula for the distance it takes a spinning Projectile to become unstable can be found in Munks formula

Or you can use an FN fired from the correct twist rate and not bother with Munk at all.

quote:

Originally posted by boom stick:
So faster twist at same velocity penetrated farther and straighter

Hmmmmm...

Faster velocity same 1:12 twist farther and straighter

Hmmmm...

Jim
"Life's hard; it's harder if you're stupid"
John Wayne

quote:

Or you can use an FN fired from the correct twist rate and not bother with Munk at all.

quote:

Originally posted by ALF:
Micheal:

Munk may not know you, you may not know of Munk, that's ok however if there is any pontification or logic discusiion to be had about rate of twist or best rate of twist and bullet stability in a target or if bullet rate of twist has any bearing penetration then then perhaps you should be introduced to Munk.

quote:

Originally posted by someoldguy:
[QUOTE]Or you can use an FN fired from the correct twist rate and not bother with Munk at all.

quote:

Originally posted by ALF:
So here is a question to all based on that statement "just use a FN"n bullet and all is solved.

1. Is a FN stable in flght on the way to the target and if those who claim it is is why then do we to spin them?

And to follow on if we spin them faster do we actually make them more stable? yes we improve the stability number ( static stablity) but what about the two other parameters of stability namely dynamic stability and tractability?

2. From this, are they ( ffN's) more or less stable than pointed bullets fired from the same gun in air?

If the same bullet weight and caliber one pointd ond a FN fired from same twist gun in air..... which is more or less stable in air?

What confers that increase or decrease in stability based on the nose shape?

3. Once the impact the target based on our knowledge of impact mechanics by all accounts all that has changed now is the value p = target density, and Coefficient of drag of for the target.

Is the FN stable or unstable ? ( ie is there a overturning moment present when the bullets transitions from air to target? who says yeah and who says neh?

If your answer is yeah, there is a overturning moment present, how then is our bullet going to counter it?..... Because if it's there is doing to be huge based on the huge defferential between Cd from air to target.

quote:

Originally posted by ALF:
So here is a question to all based on that statement "just use a FN"n bullet and all is solved.

1. Is a FN stable in flght on the way to the target and if those who claim it is is why then do we to spin them?

And to follow on if we spin them faster do we actually make them more stable? yes we improve the stability number ( static stablity) but what about the two other parameters of stability namely dynamic stability and tractability?

2. From this, are they ( ffN's) more or less stable than pointed bullets fired from the same gun in air?

If the same bullet weight and caliber one pointd ond a FN fired from same twist gun in air..... which is more or less stable in air?

What confers that increase or decrease in stability based on the nose shape?

3. Once the impact the target based on our knowledge of impact mechanics by all accounts all that has changed now is the value p = target density, and Coefficient of drag of for the target.

Is the FN stable or unstable ? ( ie is there a overturning moment present when the bullets transitions from air to target? who says yeah and who says neh?

If your answer is yeah, there is a overturning moment present, how then is our bullet going to counter it?..... Because if it's there is doing to be huge based on the huge defferential between Cd from air to target.

quote:

Originally posted by ALF:
Actually we cant meet the good Dr. Max Munk for he is no longer here, he passed away in 1986.

However if you have ever wondered about how they got to send rockets into the sky or how wings work or anything that flies ( like bullets) thank him. Studied once with Prof Prandtl ( now some here may have seen that name before )

As to the terminal behaviour of a bullet in a dense medium his slender body theory of penetration is at play.

Whith that said we leave it be for what it is..... the rest can ponder the why and wherefore of what bullets do will do between the comedy and sports pages of your local newspaper.

Perhaps if the result is given to enough "spin" no pun intended off course, it to may find its way into some copy of a popular AR supported hunting rag ang get reproduced as fact

Jim
"Life's hard; it's harder if you're stupid"
John Wayne

quote:

Originally posted by ALF:

quote:

So as a favor to the mathematically challenged but ardently interested AR participant…as you have the knowledge of the studies and mathematical computations of the late 20th century to current day experts as well as field experience…can you utilize this knowledge to compute the optimum bullet shape, bullet density and bullet velocity as well as required rifle barrel twist rate to assure optimum performance against the most dense heavy boned DG animals at the 15yd-25yd range and then again for the say 40yd-50yd range as these two ranges are obviously the most hazardous to the hunter.

The answer is in short, No I cannot nor can anyone else for that matter, not within the limitations of our ballistics system in use. Hence our propensity to go about business usually totally "overgunned" for the job at hand (based on the increasing size of bore and guns taken to Africa to do hunting with) 458 Lotts and 700 "whatsemboomers" are hardly needed for more than 96 % of game one is going to encounter.

Our "problem" if you wish lies in the choice of a weapon and bullet that has the least amount of recoil, has the greatest degree of accuracy and delivers a bullet that will do what is required of it. Just enough to do the job.... it is here where we have to know what our bullets do.

Anyone can shoot through a elephant with a kinetic energy penetrator shot from a Rheinmetal 120 mm Smoothbore gun, We have the math, we have the designs, we have at this time the most awesome firepower in terms of armor penetration known to mankind !
However it is not in the realm of most modern big game hunting guns to to the same on the same elephant.

Nor for that matter to come up with a small personal shoulder fired arm that is perfectly effective on man

The math is not the problem, we can use the simple Alekseevski- Tait equations to calculate how our super bullet must look like, problem is no one has actually sat down and figured out what the compounded differential density of Elephant skull, skin, muscle etc is to apply the math.

We can build guns and bullets that will go though a hundred men standing in line, but whether the platform would be practical from a personsal weapon sense ... unlikely.

I already know what my bullet will look like.

It will be a sabotted fin stabilized or tail dragged stablized slim bodied small meplat FN Flechette. ( no nead for Rifling, smoothbore all the way ! ) The thing will be made of tungsten and it will take out a dynosaur seated in a armoured car complete with body armour. And to any of its kin behind take care cause that bullet will do a couple of others too.

quote:

It will be a sabotted fin stabilized or tail dragged stablized slim bodied small meplat FN Flechette. (no nead for Rifling, smoothbore all the way !) The thing will be made of tungsten and it will take out a dynosaur seated in a armoured car complete with body armour.

quote:

The answer is in short, No I cannot nor can anyone else for that matter, not within the limitations of our ballistics system in use. Hence our propensity to go about business usually totally "overgunned" for the job at hand ... are hardly needed for more than 96 % of game one is going to encounter.

Our "problem" if you wish lies in the choice of a weapon and bullet that has the least amount of recoil, has the greatest degree of accuracy and delivers a bullet that will do what is required of it. Just enough to do the job.... it is here where we have to know what our bullets do.

Jim
"Life's hard; it's harder if you're stupid"
John Wayne

quote:

Originally posted by ALF:
Someoldguy:

A tip perhaps

The formula for the distance it takes a spinning Projectile to become unstable can be found in Munks formula

To anwser your riddle of the distance it takes for the bullet to tumble. You need to figure out the following.

1. what effect the resistance this target has on the impact velocity of your bullet ie the coefficient of drag for this paper target..... I have to warn you though that the most common source of error in testing is because the target ia often inconsistant.

Tests done by various defence contracted authors all confirm, the biggest cause of inconstatant data lies with the consistancy of the target.

2. you need to know more about your bullets. Length, transverse moment of inertia and where the CG is

3. You need to know what impact angle of attack is ? so unless you have a high speed camera that can capture moment of impact and its set up so you ccan do the measurement . good luck

One you have all the data, some serious math follows and you come up with something that looks like this.

The constants are "target medium" dependent.


and graphs that look like this



or one can all skip it and simply go to the various journals of trauma nand forensics and find the various articles and reports done on the very subject

quote:

Originally posted by someoldguy:
Okay, I've had a couple of Flintstone vitamins, so now I'm good to go with more geek stuff.

I found something interesting from my personal long-version penetration estimator that I'd like to share. It's like anything else that's mathematical/scientific/somewhat simple. It's not always perfect at predicting real-world results, but it gets reasonably close IMO. And I think I've found the two missing variables that make the thing work: The density and the compressive strength of Michael's test medium. (Which, despite the obsessive nitpicking of the some of the "3P crowd," appears to be reasonably well consistent.)

For the .500 B&M Super Short with a 400 grain bullet and an impact velocity of 1851 fps and a twist rate of 1:18. My model says that the penetration depth "should" be about 45 inches. However, the bullet becomes unstable at about 31" penetration and goes out of the box at 35". Going back into the formula and using Newton's law, I find that the velocity at 31", where the instability occurs, would be in the neighborhood of 1025 fps. With a twist of 1:18, this means that the revolutions per minute would be 1025 x 720 / 18 or 41,000 rpms. Okay, remember that.

The next was the same bullet with an impact velocity of 1847 fps and a faster twist of 1:12. The penetration depth "should" still have been about 45 inches, but it veered off at 37-39 inches. The estimated velocities where the bullets went unstable was much lower at 764 fps and 657 fps respectively. In rpms, this would be between 39420 and 45840 rpms. (An average of just over 42000 rpms.)

Now, the last test with an impact velocity of 2170 fps. The penetration depth "should" have been just over 49", but it stopped at 45". At this depth in my model still showed a velocity of 667 fps or just over 40000 rpms.

What I'm trying to point out with all this is that there appears to be an rpm range where a bullet becomes unstable and doesn't perform in the way it should. (In this case, in the neighborhood of 41000-42000 rpms.)

I don't know how much more evidence one needs to show how twist rate bears at least an indirect relationship to penetration!

Jim
"Life's hard; it's harder if you're stupid"
John Wayne

quote:

Originally posted by ALF:
RIP

None of the above regarding being a bully, not at all, just cannot sit still and have someone tell the world the earth is flat when we all know it's round !

Micheal posts the results, the results do not quite gel, some are sort of what can be called, "ball park" and what is to be expected but then some are clearly not? ( and it does not take a rocket scientist to see why not)

Now based on this statments and assumptions are made trying to explain away the results; for instance spin rate is responsible for the "better performmance" ?????

How could it be when the test is not even set up to test for the effects of spin rate?

Or increase in velocity gives the increase in penetration, Yes really did you actually test for it or think you were, Oh and those Barnes Buster bullet's they are worthless, no good based on what ????? these tests? Or Sectional density plays no role in ballistics, really, if it dont how in sams hell does your gun shoot?

Oh yes my favourtite AR'sm.... that infamous Supercavity the root of all cause of many wonderous things when walk about on the Ivory trail.

To misquote the good Mr Mel Gibson in Braveheart. These bullets and their "cavities " would "consume the English ( elephant) with fireballs from their eyes, and bolts of lightning from their arses"

You can use paper, you can use sand, you can use wood, but before you do perhaps take a look at what the big boys with the dark glasses say about their tests.

It's for free, google it Go check it out, even that boyoh ! Rathcoombe says it's so !

Oh as we love misquoting from Mr MacPherson ( hope I got the Spelling right this time and it's the "Second Printing" ) bottom of page 64, just before 65 the stuff on mystics we see the Kinetic energy of rotation is always less than 2% of the translational kinetic energy...... it is not included in conventional ballistics and properly so" hell coudnt have said it more plainly could we now?

But they the guys with the dark glasses and white coats who work behind high fences have already done the math..... so somwhere in there it calls for bullets with a certain density, says velocity is important, says bullet length is important, says target density is important..... hmmmm lets see now if we are going to test for velocity, then by jove all else must be equal..... then the test will be valid.... well sort of as long as our bullets dont stray, dont erode or deform. what about angular velocity, nope sorry they dont say anything about it.... they say in the fine print yes it's part of the scene but the contribution so samll dont need to even mention it. but off couse we can test for it by keeping everything exaclty the same just shoot the bullets from different twist barrels....... but dont forget everything must remain constant, just the twist may change !

Wood is valid, paper is valid, sand is valid , you can even make clay dolls if you want !

But ! and that is a very very big but, you had better make sure that the density, the degree of hydration and the quality of that mass of paper or whatever you are using for your tests is exactly the same between each and every shot, before going about uttering words about comparison, this bullet or that, this twist rate or that? because if it's not the tests are worth not the smell of the powder you got when they were done!

You guys are the ones blathering on about twist rate, you are the ones singing the praises of the 1:10 barrel or the, 1:12 . Do you really know what you are singing about and proclaiming? When someone points it out to you you get all pissy ! You sing the words but refuse to accept the meaning of the words or even acknowledge the writer of the song!

Why exactly do we spin our bullets?

Have you really given it some serious thought ? Well if you do you will come head to head with Dr. Max Munk, His formula for for the Overturning moment is why we spin bullets, why we should or should not use certain spin rates for certain applications, it determines the abosolute length limit of a spin stabilized bullet. It also tells us why when the target is impacted bullets go South.

I am practical ! very very practical, I do not believe in chance luck or fate or voodoo for that matter...... so if you are going to sing spinrate and RPM to me , or these bullets are good or no good based on whims you have be ready to sing the whole song, not just the chorus, the same goes for just about every other song that's sung here on AR

quote:

Well if you do you will come head to head with Dr. Max Munk, His formula for for the Overturning moment is why we spin bullets, why we should or should not use certain spin rates for certain applications, it determines the abosolute length limit of a spin stabilized bullet. It also tells us why when the target is impacted bullets go South.

quote:

Originally posted by ALF:

quote:

So as a favor to the mathematically challenged but ardently interested AR participant…as you have the knowledge of the studies and mathematical computations of the late 20th century to current day experts as well as field experience…can you utilize this knowledge to compute the optimum bullet shape, bullet density and bullet velocity as well as required rifle barrel twist rate to assure optimum performance against the most dense heavy boned DG animals at the 15yd-25yd range and then again for the say 40yd-50yd range as these two ranges are obviously the most hazardous to the hunter.

The answer is in short, No I cannot nor can anyone else for that matter, not within the limitations of our basllsitics ssytem in use.

Jim
"Life's hard; it's harder if you're stupid"
John Wayne

quote:

I, as well as I believe other participants, would like you to continue your bullet depth computations utilizing any beneficial information that you might derive from Alf’s contribution.

Thanks in advance.

quote:

Originally posted by ALF:

To misquote the good Mr Mel Gibson in Braveheart. These bullets and their "cavities " would "consume the English ( elephant) with fireballs from their eyes, and bolts of lightning from their arses"

the big boys with the dark glasses say about their tests.


But they the guys with the dark glasses and white coats who work behind high fences

quote:

Sitting upon the throne, the lord our God turns to his "right" in which there sits michael458 at the lord's right hand. He says to michael458, son, you must change your handle to michael500, for I am giving to you rifles of various 500 caliber in which to smite the beasts of the earth.

quote:

Alf,
You seem to be quite the intellectual bully.
You know what is said about intellectual bullies?
They are usually overcompensating for one of three things:
1. They were nerdy teacher's pets in junior highschool and got physically bullied on the playground or school bus.
2. They are tortured by the memory of flunking highschool calculus, before they got religion and started paying attention in class.
3. They have tiny penises.

quote:

Originally posted by ALF:

The problem if we wish is the issue of projectile stability, how to control it and at this point given our current ballistics sysetm the FN bullet is what does the job.

quote:

Originally posted by someoldguy:

quote:

Sitting upon the throne, the lord our God turns to his "right" in which there sits michael458 at the lord's right hand. He says to michael458, son, you must change your handle to michael500, for I am giving to you rifles of various 500 caliber in which to smite the beasts of the earth.

Ordinarily a person would have to pay for such entertainment as we provide. But we get it all for free, here in Michael's thread!