Gerard,

I am not up to any tricks; we are simply debating SD as a concept. Perhaps we see its roll in a somewhat different role even though you say at the end that we essentially agree with each other and that is a good thing if we can. You stated your view and I stated mine. SD has its place, but cannot be used in a stupid way as a single figure exclusively – I said so many times and illustrated it with many examples as well.

RIP,

Yes I did reregister again with AR as my password did not allow me to get in. I wrote 3 times to AR between Dec 19, 2006 and Jan 31, 2007 to enquire what was wrong with my password. I never got a response. As I was not sure whether Saeed ever received my e-mail regarding this matter I decided to reregister. I was not advised that I have been banned and that comes as a surprise to me.

The â€hate speech†that you refer to is essentially all quoted stuff that is available on the internet. My point was to bring it to the surface rather than to wipe it under the carpet and let the subject of blaming everything on the Palestinians and the Israeli’s appear so spotless. I pointed out with various quotations the history of the Jews leading to the current conflict in Palestine. For that I was castigated and called ugly names. The Political Forum seems to protect some guys that they can say what they like against the Muslims but it is not OK if we turn the spotlight on the Jews. 500 Grains for example made a number of vicious statements against Palestinians, Lebanese and Iranians and I suppose that must go unattested, and he is not the only person in this category. Drg also had a lot of ugly things to say about me as he took an opposing view. Where is the equity or the even hand? I did not attack a particular person that conferred with me, other than defending myself, but rather that there are so many background information (some which is dubious) that some conveniently seems to forget. Open debate is a good thing even if we differ with each other – there is no other way then to learn new things. Just recently we learned on the news how Israel used phosphor bombs and cluster bombs on the Lebanese that killed civilians. I cannot be silent about this and all double standards for that matter.

Regarding the reference to shooting “nigger balls†that puzzles you, we do sell sweets in SA that we call nigger balls – it is a sweetish candy pressed in round balls about half an inch in diameter and it comes in an array of colours. So there is nothing bad about it. I thus referred to shooting sweets rather than bullets.

If Saeed indeed feels that I must leave I will, but then I expect at least a notification in that regard from him without any arguments. Trusting that he can at least see that the cloud of smoke over the last 2000 years is none of my making, but somehow we have to make sense of it. Every thing cannot just be blamed on the Muslims when the West is meddling in their affairs – for every action there is a reaction.

May the icy wind blow softly upon you and the evil spirits pass you as the tone in your voice needs some dampening.

Warrior

quote:

Originally posted by Gerard:
As in Seinfeld?

Gerard,
You got it.

Multilingual and fluent in American television too! Wow!

"Kramer" is that has-been sitcom character who has lately become a flop as a stand-up comedian, and got into hot water over the "N" word.

The "Kramer" handle would definitely be approriate for truvelloshooter-warrior's next reincarnation.

RIP,

quote:

The â€hate speech†that you refer to is essentially all quoted stuff that is available on the internet.

Do you think that includes the death threats he made and the references to making soap also? I wonder Who "Warren" is? An attempt at masking his real identity maybe? N***** balls have not been for sale for more than a decade now. I wonder where he gets his.




Sorry about that jy, but you probably have more on Sd now than what could possibly be useful to you, or anyone else for that matter.

Don't be shy to ask again.

Gerard,
Warrior's latest comedy routine must have been seen to have socially redeeming value. The punchline was that he admitted that Warrior is Bekker/Truvelloshooter.

Saeed's policy is to allow him to get a new ID and carry on until becoming too offensive again. References to candy are apparently "not too offensive."

Warrior,
Carry on.

quote:

Originally posted by Gerard:
JonA,
Please translate to English. The engineer is not available.

It's simply the area of a circle in terms of diameter, which shows the direct relationship to the SD input. While it may seem more complicated than pi*r^2, it is used often in the Engineering world because so many parts are identified by their diameters--it makes for a more transparent (easily followed and duplicated or modified at a later date) analysis when you know which part is in which equation.

quote:

Wink,
You have a PM.

It must not have come through. Please re-send.

Earlier it was stated that a particular non expanding projectile at 1550fps showed no less penetration than an identical one traveling faster, if thats the case what happened to all that extra momentum from the higher velocity?

Another question,
If there was no extra penetration from the higher vel/momentum, what would happen if did not run it faster,but instead used a heavier non expanding bullet of same cal. and launched it at the same 1550fps velocity?..the result would be more, less, or same penetration? ....or does its extra momentum also mysteriously disssapear and contribute to nothing??

The ideal set would be if we increase the weight of a given calibre bullet without increasing its length, technically giving better penetration cause of less drag right? eg,ie; if we stuffed a tungsten core up the butt of a GSC bullet.

Woodjack; That was my point exactly. By the time the faster bullet had slowed to the velocity of the slower one it would have penetrated some distance. How then could the slower one pass it.
Good Luck!

Hawkins,
they all seem heavy on the science and formulas, but it dont explain the logic of things!

JonA,
If this statement is true: BC = Mass /(Cd x cross sectional area)
and Sd = Mass/cross sectional area)
how would one complete the statement: BC =
using Cd and Sd?

Woodjack and Hawkins,
There are logical explanations for your questions.

quote:

Earlier it was stated that a particular non expanding projectile at 1550fps showed no less penetration than an identical one traveling faster, if thats the case what happened to all that extra momentum from the higher velocity?

The statement was that maximum penetration was reached at 1550fps. Although not mentioned implicitly, one deduces that penetration below 1550fps and above 1550fps was less. It is no coincidence that "hard cast" lead bullets will start expanding quite well from 1500fps and up. So I will say up front that El Deguello referred to the test in good faith but the source was inaccurate in their observation or statement of fact. Over 1500fps, lead bullets will expand if fired into any kind of halfway acceptable test medium. The results are therefore logical. The increasing level of penetration up to 1550fps was the result of increasing the momentum applied to the cross sectional area. At 1500 fps the bullet starts expanding as a result of stagnation pressure that increases as the square of velocity. The point is reached where expansion increases the cross sectional area enough, so that the ratio of momentum to XsA is less favourable than what it was at lower speeds and the result is less penetration.

quote:

If there was no extra penetration from the higher vel/momentum, what would happen if did not run it faster,but instead used a heavier non expanding bullet of same cal. and launched it at the same 1550fps velocity?..the result would be more, less, or same penetration? ....or does its extra momentum also mysteriously disssapear and contribute to nothing??

I think you are asking what would happen if you run it at the same speed but increase the weight. The answer is logical. If it is a lead bullet, the increase in weight (and Sd) will tend to result in more expansion at 1500fps than the lighter bullet at the same speed. Penetration may not increase because the increased expansion causes more drag for the available momentum to overcome. If it is a solid copper or brass bullet, it will not expand and penetration will increase because Mo/XsA has increased. If the heavier lead bullet does not show an increase in penetration due to expansion and therefore the reduction of Mo/XsA, the momentum does not mysteriously dissapear, it is countered by the increased drag.

quote:

if we stuffed a tungsten core up the butt of a GSC bullet.

Several things would happen: Bullet imbalance will increase and reduce the accuracy potential of the bullet. The increase in weight brings a reduction in speed. The result of this would be larger groups, more wind drift, longer time of flight and a more bowed trajectory. You will have more misses and badly placed shots. The reduction in speed will also reduce the momentum, negating any momentum increase as a result of the extra weight. The overall result is therefore similar momentum, less energy and less accuracy. It is a no brainer.

quote:

That was my point exactly. By the time the faster bullet had slowed to the velocity of the slower one it would have penetrated some distance.

In situations where extra speed results in a reduction of penetration instead of an increase, it simply means that the point is reached where the particular speed was high enough to expand the bullet. The higher the speed, the more the expansion.

quote:

How then could the slower one pass it.

Because, by the time the faster bullet reaches the speed of the slower one, it has expanded to a larger diameter than the slower one. So you have two bullets of the same weight, traveling at the same speed but one is of a larger diameter. Obviously, if both have the same weight and speed, momentum is the same and the bullet with the larger diameter will penetrate less. Over the entire path in the medium, if the slower bullet maintains on average a more favourable rate of expansion to momentum, it will go deeper. Mo/XsA in action again.

quote:

they all seem heavy on the science and formulas, but it dont explain the logic of things!

How did I do?

Of course if a bullet expands it will lose penetration. It was stated early in this thread that identical non-expanding bullets would penetrate deeper at slower velocity. It was furthur stated that tests proved this.
I'm still waiting.
Good Luck!

Thanks Gerard,
My postings main aim was to question the integrity of the statement quoted below.
it just logically didnt/doesnt make sense.

quote:

Originally posted by El Deguello:
Yes, recently a penetration test involving .45 caliber rifles, found that in the .45/70, maximum penetration for a 420-grain hard cast bullet was produced at a MV of 1550 FPS. Any significant increase in MV resulted in a measurable degradation of penetration, even though none of the bullets expanded at ANY of the impact velocities........

/

Alf,
In theory you are right and, for certain types of bullets it is a factor to watch. In practise what I have observed is that there is no such thing as an absolutely non-deforming bullet. Make them from what you will, sooner or later a speed can be reached when the bullet will deform or break and then we are back to retained weight, broken bullet shape and Mo/XsA. With FN bullets, in the typical larger calibers, I could only get them to expand to larger than caliber by shooting them into steel drums filled with wet sand (378 Weatherby and 460 Weatherby). I have only succeeded in reliably demonstrating reduced penetration at increased speed with HV bullets, at muzzle velocities over 4400fps. With jacketed lead bullets it is much different and then

quote:

This means that at lower velocities the same bullet may well penetrate better than at high velocities within a velocity window.

There will be a velocity window where in the bullet will have best penetration.

becomes a factor to watch carefully.

quote:

Originally posted by Gerard:
how would one complete the statement: BC =
using Cd and Sd?

BC = SD * (Cd of the Defined 'G' Function Std. Bullet)/(Cd of your bullet)

From:

BC = SD / Form Factor

and

Form Factor = (Cd of your bullet) / (Cd of the Defined 'G' Function Std. Bullet at a particular velocity)

As you can see, your first equation: (BC = Mass /(Cd x cross sectional area) needs a constant (which will change with velocity) to give a BC number correlated to a particular drag curve.

But in the end, you can see it just can't get away from Sd (or Mass/cross sectional area or whatever you want to call it).

.

quote:

Originally posted by ALF:
Is that not what we have saying all along?

Yes. It is.

ALF; What you say about a "window of velocity"
for maximum penetration is correct fot
EXPANDING BULLETS. We were discussing non-expanding bullets.
Good Luck!

/

Those that did not see the following field tests may find this of interest:

Dr Ed Ashby, concluded in 'Maximizing Monolithic Bullet Performance' (June 2000 Man Magnum), that better penetration was attained with Barnes-X bullets fired at modest velocity.

"The penetration disparity between high-impact velocity and low-impact velocity also persisted with the 30-06 Spr. At 2,792 fps, the 165 gr Barnes-X bullet penetrates far less deeply than it does at a velocity of 2,484 fps. At the higher velocity it frequently failed to penetrate even big chest shot warthogs completely. Thus far, there have been no failures to exit any animal shot at the lower velocity. Again, these tests involved a significant number of shots at each velocity level."

Dr Ashby used 45-gr Barnes-X bullets in a .22 Hornet and .22-250 and the very same bullet showed far superior penetration at moderate Hornet velocities as opposed to higher velocities of the 22-250 Rem. Just look at the marked differences in penetration depth.

a) Dropping the MV from 3,571 to 2,651 fps gave more than double the penetration! (117%)

b) Dropping down to a MV of 2,442 fps improved penetration by a further 17%.

c) From the highest velocity to the lowest velocity penetration improved by 153% - a phenomenal difference.

Clearly there is a 'velocity window' as Mo/Xsa cannot be optimized ad infinitum as the in-target drag gets increased with increased velocity due to changes that happens to the bullet such as differing deformation of the expanding petals (set-up rate, shape & diameter) and loss of bullet mass and increased stagnation pressure.

Thus we know that the equation of Mo/Xsa = SD x V is not a pure linear relationship - there is a definite window in which the equation would have value - not in perpetuity.

Warrior

This is why a good bullet design should give good terminal performance at the highest probable impact speed. As it slows down, in smaller cases or over distance, it can only improve.

Regarding Sd, I thought we are all in agreement about the subject. Why are you guys still arguing? Is it momentum that is keeping you going?

I am new to this site my spelling is terrible and don't know the pecking order yet. You guys sure seem to have one. It seems to me that not one of you answered his question. It appears he was asking about target shooting not hunting. Shooting at paper seems to make terminal balistic a bit mute. I believe that most of the posts are dealing in only two dimensions. SD along with iths shape or form has a significant effect on a bullet in a cross wind. Given the same meplat the same olgive the same form on the base the same velocity and the same construction a bullet with a higher SD will not drift in the wind over the same time peiord as much as one with a lower SD. Notice I did not say diameter or weight.

All this arguing about the terminal ballistics is a little much also. I failed to notice where anyone mentioned that as the bullet begins to mushroom or break apart or deform that SD changes and it is a dynamic change until the bullet no longer has enough energy to bend twist or fragment anymore. The changes in shape of the bullet are related to SD but it is only one variable. Construction of the bullet, its meplat its olgive its energy the media it is traviling through all must be considered and are dynamic over the entire time the bullet is traveling in the media. Because only God knows everything, Mathmatics can only give us a SWAG. Saying that SD has no effect on a bullet or penitration just because it is beyond our current ability to use it in predicting terminal ballistics is as silly as saying the universe can't exist because we can't use math to determine where matter and energy came from.

It's still a useful number, and bullets are still around 2 - 4 calibers long for rifles and 1 to 2 for handguns. I doubt that will be changing anytime soon.

If you fire a disk of .30" diameter but only .1" thick you're asking for disaster, even if you can accelerate it to 7000 fps. That projectile would have a poor performance for a number of reasons and it can be easily recognized as an inappropriately low sectional density. There are other ways to numerically indicate it's a bad idea as well.

LorenS,

I whole heartedly agree with you. I am a hunter first and only a shooter as a result. Sectional density is very important to performance. At the end of the day I will choose a heavy for calaber bullet over a light one for any big game including deer. I can't prove it mathmatically but I know what I see. A well constructed bullet with good SD will out penetrate the same type of bullet with a low SD. given that all else is equal. The Idea that a TBX has a lower SD and out penetrates a jacketed bullet doesn't validate anything for me. It may have started out with lower SD but after the point of impact, it just means that as it traveled through the media it was able to maintain a form that possesed a better over all SD during its trip. I am very careful about the bullet I choose for hunting I have used TBX, Failsafe, Nosler Partitions gamekings balistic silver tips acubonds corelok and a few others. They all can kill but I fell that I owe it to the animal that I am harvesting to choose the best bullet for the job at hand. Sectional density is a big part of my decision. Do I think a TBX is better on elk than a accubond? Yes I do. Do I think a TBX with a higher SD is beter than a TBX with a lower SD? Yes I do. Do I think a very small calaber bullet with a higher is better than a much larger calaber with a slightly lower SD? Of course I don't. However in calabers that are very close with bullets of simular construction, weight and velocity the smaller calaber is going to penetrate better SD is very important to penetration and wind drift and therefore very important to consistant humane harvesting.

quote:

Originally posted by Game King:
I am new to this site my spelling is terrible and don't know the pecking order yet. You guys sure seem to have one.

Hey Game King

Stick around. Honest practical answers like yours trump pecking order every time.

quote:

Originally posted by Game King:
I am new to this site my spelling is terrible...

Welcome Aboard! You will fit right in with those credentials.

quote:

... SD along with iths shape or form has a significant effect on a bullet in a cross wind.

Agree, that is the Ballistic Coefficient, and it does matter at distance.

quote:

...I failed to notice where anyone mentioned that as the bullet begins to mushroom or break apart or deform that SD changes and it is a dynamic change until the bullet no longer has enough energy to bend twist or fragment anymore.

Absolutely. As the Bullet begins to Expand, the SD begins going down, and as it goes down, the Penetration also goes down.

quote:

The changes in shape of the bullet are related to SD but it is only one variable. Construction of the bullet, its meplat its olgive its energy the media it is traviling through all must be considered and are dynamic over the entire time the bullet is traveling in the media.

Excellent understanding of what actually transpires.

quote:

From Game King's second post:
... A well constructed bullet with good SD will out penetrate the same type of bullet with a low SD. given that all else is equal.

That sums it up in a few simple words.
---

I hope the originator of the Thread "jy" is still around to read Game King's comments. "jy" never responded to my earlier question, so he may be gone.

Game King,
There is no pecking order here. Those with no experience voice opinions shoulder to shoulder with those who have a lifetime of experience. If you are not used to irreverent treatment, you will soon be. Welcome.

quote:

Game King:
It seems to me that not one of you answered his question. It appears he was asking about target shooting not hunting.

Here is his entire first post:
"What is this Sectional Density? How do I use the numbers to help my shooting?
THANKS
Jerry"

The replies covered both aspects, hunting and target so, not knowing the actual application, a general cross section of information was presented, I think. Given his actual question, I am at a loss how you conclude he was asking about target shooting.

quote:

Given the same meplat the same olgive the same form on the base the same velocity and the same construction a bullet with a higher SD will not drift in the wind over the same time peiord as much as one with a lower SD.

Two points here: Firstly, why would anyone shoot a light bullet at the same speed as a heavier one? Lighter bullets are supposed to be used at higher speeds and then your statement does not hold water.

Be that as it may, secondly, you are correct about the lesser drift of the longer bullet but the reason for the lesser drift is that it has a better form factor than the shorter bullet. Sd is coincidental to the lesser drift and not the reason. Proof of my point of view: Take two monometal bullets of the same weight and caliber and fire them at the same muzzle velocity. One is a flat nose solid and the other is a spitser long range bench bullet. Same Sd, same muzzle velocity but radically different external and terminal ballistics. So, in the real world of practical application, Sd has little value. In a contrived example with little practical application, Sd can be shown to be the cat's whiskers but who cares?

quote:

I failed to notice where anyone mentioned that as the bullet begins to mushroom or break apart or deform that SD changes and it is a dynamic change until the bullet no longer has enough energy to bend twist or fragment anymore.

You must have missed it. Right on the first page I said: I have some opinions on Sd

LorenS

quote:

That projectile would have a poor performance for a number of reasons and it can be easily recognized as an inappropriately low sectional density.

Mostly it would have poor performance as a result of bad BC and no momentum compared to its frontal area. Sd is incidental to your example and the example is impractical. This is the problem I have with Sd. It exists as a fudge number but has no practical application when trying to stand on its own. Saying that a bullet with high Sd will penetrate better than one with low Sd is absurd. Sd always has to be qualified with the real reasons.

Game King

quote:

A well constructed bullet with good SD will out penetrate the same type of bullet with a low SD. given that all else is equal.

All else is never equal. That is the old crutch Sd always leans on and it is an artificial situation. Practical examples show that it has no value as a likely indicator of terminal or external ballistics.

The bottom line is that we should stop teaching new shooters that Sd is important. Instead we should be telling them about momentum and cross sectional area. We should be educating them about bullet construction and the balance between bullet length and twist rate, given the variables of distance and application. This will bring about a better understanding of what is required for humane harvesting.

We have an entire generation of shooters who think only big Sd numbers and that is such a pity.

quote:

Originally posted by Gerard:
but the reason for the lesser drift is that it has a better form factor than the shorter bullet. Sd is coincidental to the lesser drift and not the reason.

Please review the math above. With the same form factor (or Cd) if you increase SD you increase BC.

quote:

if you increase SD you increase BC.

Coincidental, because if you vary the speed of two identical bullets, you also vary BC, varying wind drift, while Sd has not changed.

Respectfully, I would like to appologize for my earlier "used car salesman" comment, Gerard. It's clear you really are just....uhm...."mathematically challenged" if that's a politically correct enough term. Directly Proportional "Coincidental." Not by a long shot.

quote:

With the same form factor (or Cd) if you increase SD you increase BC.

Ok, explain to this mathematically challenged person how you will increase the Sd of, for example a .30 caliber monometal bullet, while keeping the Cd unchanged.

.

quote:

Coincidental, because if you ...

Coincidental ... you mean by chance or by a stroke of luck, not so.

BC = SD/i (simplistic equation)

SD is the numerator in the equation.
When SD goes up and i stays the same, then BC must go up.

There are obviously other considerations as well, that would alter the curve somewhat. The math of which needs an advanced univeristy mathematics course. The first 3 chapters in Geoffrey Kolbe's book (A Ballistic Handbook) deals with some of the basic math involved. BC's can get very complex and there is not a single finite solution - drag curves vary depending on the mathematical model employed. That is why Pesja's curve and equations differ from the Gavre Commission (1873), Mayevski (1883), Ingalls (1900), Dr c Cranz (1912), etc. The maths will probably fly over our heads as a project all by itself, but perhaps Jon A could give us some pointers.


Warrior

Alf,
Over the last thirteen years we have used a variety of methods. Simplistic calculation, double chrono, comparison to standard form nose shapes and so forth. None of them really satisfactory. Short of building a 300m tunnel and setting up a weather station to record parameters, we now use next best method which is design software that is quite accurate in more ways than just calculating BC. It is a lot of work to recalculate all our bullets and, at this stage, it is not a priority to rework the entire range. It will however bring a uniformity of method that will be useful in the future. New bullets have the full new info ( Example ) and, as I am asked for the info for existing bullets, I try to add them as quickly as time allows.

quote:

When SD goes up and i stays the same, then BC must go up.

There is the problem. Mathematically it can be done but in practise, when comparing two similarly constructed bullets, when Sd goes up, i cannot remain the same. The example given remains coincidental.

Sure i will change slightly; it speaks for itself.

From QuickLoad:

150 gr Speer SP .308 bullet - SD = .226, i = .599, BC = .377
165 gr Speer SP .308 bullet - SD = .248, i = .559, BC = .444

The basic point is as we moved to the heavier bullet, the BC went up.
That is by virtue of a better SD and a better form factor, because if the 165 gr bullet also had an i equal to the 150 gr bullet, the BC would have been .414 instead of .444, so yes, it also contributed to a slightly better BC. Thus neither SD nor i is irrellevant or coincidental - they work hand in glove!

Warrior.

If you increase the speed of the 150gr bullet, the BC increases. If you decrease the speed of the 165 gr bullet, the BC decreases. Yet the Sd for neither has changed.

quote:

Sure i will change slightly; it speaks for itself.

That is by virtue of a better SD and a better form factor

These parts of your post illustrate very well that Sd always has to lean on the crutch of the real reasons. It remains coincidental and a fudge number.

quote:

The basic point is as we moved to the heavier bullet, the BC went up.

How about this: In .30 caliber compare a 200gr round nose, flat base bullet with a 180gr spitser boat tail match bullet. Now the BC has gone down where the Sd has gone up. Fudge number.

It is not a fudge number - it is the inter-play between SD and i. Both are still there.

Warrior

When you keep a similar nose profile and boattail, the length of the shank in the middle has very little to do with form factor. Simply making the bullet longer can leave you with a slightly better or worse form factor. A good example:

175 SMK:



Top BC: .505

220 SMK:



Top BC: .629

Here you can see despite the great difference in total length, the form factor changes very little. In fact, it GETS WORSE for the 220 (it would have a .635 BC if it kept the same form factor).

Form factor changed very little actually getting slightly worse. BC went way, way up because of its increased SD. It doesn't get any more apples to apples than that comparison.

Go through their entire linup or any other linup of similarly shaped bullets for which you have accurate BC's and you'll find the form factor stays relatively constant, varying plus or minus just a bit unless big changes are made (changing a spitzer to a roundnose, adding/removing a boattail, etc). But the BC's go up and up with weight very close to proportionally.

/

Chris/Truvelloshooter/Warrior
Form is more important than weight, within a given caliber, in determining BC. Sd is not required to make the calculation. It is a fudge shorthand number that is discarded as soon as correct/precise numbers are required. The fact that mass is used in one part of the BC calculation and frontal area forms part of the calculation elsewhere, does not mean that Sd is significant. It remains coincidental that those elements = Sd. What is important is mass where it is used and frontal area, where it is used, in the equations. By your reasoning, energy or momentum could be ascribed the same importance in determining BC you attach to Sd, because if you go dig for the elements that make up energy and momentum, they are also there.

If Sd largely determines BC, why, in .30 caliber, if we compare a 200gr round nose, flat base bullet with a 180gr spitser boat tail match bullet does the BC go down where the Sd has gone up?

JonA,
In your Sierra example you have made a substantial increase in the weight of the two bullets compared, while attempting to keep the form factors close together (which is of course impossible). This is pretty close to comparing apples to apples but not quite (sort of like fudge apples).

A real apples to apples comparison would be this.
Both bullets are:
Jacketed lead core.
Weigh 220gr.
.30 caliber
(Therefore identical Sd.)
Identical speed.

One bullet is the SMK you mention and the other is the Sierra RN.


Assuming that the form factors in your example are similarish, the increase of 45gr from 175 to 220 (26%) brings a BC increase of about 20%.

According to Sierra the RN bullet BC is .335 and the SMK is .629 and that is an increase of 87%. This is apples to apples, as only one parameter has changed according to your reasoning, form factor.

As you are not mathematically challenged like me, the used car salesman, can you determine what the % change in form factor is and, while you are at it, why the SMK BC goes up with velocity while the RN BC goes down as velocity increases?

When you are done, tell me again that Sd is the major factor in determining BC and not a coincidental fudge factor that happens to be sort of close if you massage the "ifs" and "buts" hard enough.

Alf,
The difficulty I have with Sd is that, as a parameter it is meaningless. The elements that make up Sd are of great importance but the trap that the shooting world has fallen into is this:

"High Sd bullets penetrate better than low Sd bullets."
"High Sd bullets have better BCs than low Sd bullets."
"High Sd bullets give better weight retention than low Sd bullets."
"High Sd bullets are better in wind than low Sd bullets."
"High Sd bullets kill better than low Sd bullets."

These are all false and anachronisms from a time when they were generally true for reasons that should not be ascribed to Sd. The link to Sd seems to exist but, in truth, the link to Sd is coincidental.

Today we know that the statements above are as misleading as stand alone statements as the nonsense around "hydrostatic shock". We should not continue to perpetrate these myths.

Ok, we have a line in the sand. Now lets do what all cilivized countries do. Lets break out our rifles and settle this. Talk is cheap. Quotes from experts only convince the chior. Math is nice but math didn't prove we could go to the moon. Neil stomped his little foot on it. Lets do this!

.284 150gr TSB VS .308 150gr TSB
.308 200gr Accubond VS .338 200gr Accubond
.277 150gr RN VS .308 150gr RN (Hornady)

Velosity at point of impact: 2300 FPS
Media: Balistic Test Tube.
Same Day, Same Temp, Same Altitude, Same Humidity

Who has issues with my testing perameters?