quote:

Originally posted by 900 SS:
rcamuglia

I conclude different

Take any rifle.
Take a specific lead core bullet available in different weights for that rifle.
The longest bullet will be the heaviest and have the biggest BC than the rest.
When fired, they will ignore wind better
At impact, they will have greater momentum
They will retain more momentum per exposed area in the medium
They will out-penetrate the lighter, shorter bullets in the line

You just dont need to calculate the SD value to know this

We both say the same thing, just say it differently.

The longest bullet will be the heaviest.
The shortest will be the lightest.
The diameter doesn't change, so this HAS to be true

Same difference

Gerard,
You either don't get it or Fudge by taking part of what I said.

I said take a specific bullet. IE the Nosler Accubond for example. Changing the weight only for .30 caliber you will find that the heaviest bullet will have the greatest SD, BC

You also fudge the velocity figures to achieve momentum and wind drift figures you want to post and probably the range at which they are measured

I also won't believe that bullets of equal construction, but with different SD's because of weight. will not reflect the same difference in SD inside the target as flying through the air or sitting in the box on the bench

quote:

Originally posted by 900 SS:

quote:

Originally posted by someoldguy:

Mass x acceleration / area

Hint hint.

Back to momentum/resistance?

Thats my favourite!

I didn't even bring that up! I was talking about tensile strength!

Good God, this is all making me crazy! Someone help me out here, please, if it's even possible.

On this page, Gerard said earlier:

quote:

These drawings/charts are obviously theory, not actual tests.

And now Gerard refers to one of these same drawings/charts, which he has already more or less rejected, when he just said:

quote:

I have asked this several times. Neither you nor Alf nor Warrior can come up with an answer. In the chart below, SD did not change. Why did the penetration depth change?

Likely no one answered because you'd obviously already dismissed the charts anyway.

This is just plain nuts! Who wouldn't be confused by all this?!

quote:

Originally posted by Gerard:

quote:

So SD in terms of the penetration proccess is in fact Dynamic

It is not. The SD has only changed. The fact that SD changed over the time it took the bullet to impact and stop, does not make it dynamic. When a factor is dynamic, it causes change in related factors. SD does not cause the changes that occur. SD is changed by the events and forces that occur.

Therefore, the impact speed (dynamic) resulted in the bullet momentum (dynamic) being countered by the drag force (dynamic). The drag force exceeded the tensile strength (static) of the bullet, causing it to deform, thereby changing the SD (static).

If the SD changes for the same projectile in the same event then it is by definition dynamic.

You dont get to change the meaning of words to suit yourself.

SSR

It's a strange, strange world we live in, Master Jack.



Warrior

quote:

Originally posted by Cross L:

quote:

Originally posted by Gerard:

quote:

So SD in terms of the penetration proccess is in fact Dynamic

It is not. The SD has only changed. The fact that SD changed over the time it took the bullet to impact and stop, does not make it dynamic. When a factor is dynamic, it causes change in related factors. SD does not cause the changes that occur. SD is changed by the events and forces that occur.

Therefore, the impact speed (dynamic) resulted in the bullet momentum (dynamic) being countered by the drag force (dynamic). The drag force exceeded the tensile strength (static) of the bullet, causing it to deform, thereby changing the SD (static).

If the SD changes for the same projectile in the same event then it is by definition dynamic.

You dont get to change the meaning of words to suit yourself.

SSR

quote:

Originally posted by Warrior:
It's a strange, strange world we live in, Master Jack.



Warrior

rcamuglia

I'm sorry to say that I have not concluded yet. The point I tried to make was that we dont need to know SD. It only confuses and doesnt add information. Comparing two similar bullets, their weight or looking at their shape/length give at least me a lot more.

.

quote:

If the SD changes for the same projectile in the same event then it is by definition dynamic.

You dont get to change the meaning of words to suit yourself.

SSR

Exactly - Dynamic doesn't mean that the change has to be caused by the factor. It just means that it isn't constant.
Therefore BC is also dynamic because it changes with velocity

someoldguy,

quote:

So tensile strength could be rewritten as:

Mass x acceleration / area

Hint hint.

Note the change in emphasis. Two static elements and one dynamic element.

Alf,
Thank you for the answer.

So it is apparent that varying the drag on a bullet, as it penetrates air, tissue, sand, wood, water or whatever, will result in penetration variation.

Drag can be altered by varying any of these static qualities (the list is not exhaustive):
1. The substance of the medium.
2. The shape of the bullet.
3. The bullet material.
4. The weight.
5. The diameter.
6. The bullet construction.

These are static qualities and, in combination, some of them will result in a combined static quality such as:

1. Weight / diameter squared = SD
2. Shape and construction determines centre of gravity.
3. Tensile strength and shape determines deformation characteristics.
And so on.

Dynamic qualities are derived from static and dynamic qualities.

1. Speed.
2. Drag
3. Pressure
4. Force
And so on.

What is also clear is that, with enough artificial circumstances set, we can attempt to isolate any static and many dynamic qualities, to prove how they influence penetration.

Saying that we use an undeformable bullet, all else equal, is nonsense. All else may appear equal but it never is.

This is why the fixation with SD is nonsense. It is an old wives tale that has run its course and has been disproved. It is time to move along.

rcamuglia,

quote:

I said take a specific bullet.

I did not go to specific model of bullet, just a specific manufacturer. Your example becomes one of those "all else equal" things.

However, examine what happens to one specific bullet. Use a 30 cal 150gr Nosler Accubond for both tests. It does not get more specific than that. This is supposed to be one of those "keep all else the same" setups where all else never is the same.

Fire one at a starting load and one at a maximum load from the same rifle and at the same medium. Only the speed differs. One will penetrate deeper than the other. This is logical but why does it happen?

Then take two Accubonds of differing weight, balance the speeds until the same penetration depth is achieved with both. The SD differs but penetration does not. Why is that? What else will change? The wound channel volume perhaps?

quote:

You also fudge the velocity figures to achieve momentum and wind drift figures you want

The speeds are not my selections. They are straight from Loadbase and are the actual speeds given by the manufacturers of ammunition, powder and bullets. You assume incorrectly and thereby insult.

quote:

and probably the range at which they are measured

Ok. Now we know that you are not qualified for this discussion. Not your fault, this is a wide subject with much to absorb and learn. The differences start at the muzzle and become greater as the bullet goes down range. One can get the momentum numbers to overlap from muzzle to whatever distance but wind drift starts at the muzzle and goes on from there.

quote:

I also won't believe that bullets of equal construction, but with different SD's because of weight. will not reflect the same difference in SD inside the target as flying through the air or sitting in the box on the bench

Remember that comment and, when you find that it is in fact so, when you have gained more experience, think back on it.

someoldguy,

quote:

Likely no one answered because you'd obviously already dismissed the charts anyway.

It is more likely that the normal mechanism of, "this question points out that I have made a mistake, so I will ignore it", has kicked in. Why else would I have to ask several times?

Cross L, rcamuglia, JabaliHunter and PI (Pontificus Ignoranus),

quote:

If the SD changes for the same projectile in the same event then it is by definition dynamic. You dont get to change the meaning of words to suit yourself.

The example below is given for the layman but holds true for finer elements and factors in engineering as well.

http://www.engineering.com/Ask...id/3744/Default.aspx

"In engineering static systems do not move, change states, or do not move / change states quickly. Examples of static systems include furniture, dishes, buildings, bridges, etc.

Dynamic systems by their very nature are change states or moving all the time or must change states be useful. These type of systems include: vehicles, entertainment equipment (radios, televisions, tape recorders, etc.), computers and printers, etc.

Note many of these systems have characteristics of the other. The case work of a computer can be seen as static, but inside there are a lot of dynamic process including the operation of the disk drives, and the flow of electrons through the wires and the processor that is the heart of the computer."

Just because an element or factor moves or changes state does not mean that it is dynamic. If I move my PC from one side of the office to the other, does that make the case of the PC dynamic? If my PC becomes redundant and I dispose of it to a recycling company and they crush the case for melting down, does that make the case dynamic? If a building or bridge is imploded at the end of its life cycle, does that make the structure dynamic?

Dynamic is that which changes state as a result of the factor itself. Static is that which does not change state as a result of what it is, in itself. It does not mean that the factor cannot be changed and it does not mean that every factor which changes, is dynamic.

Speed, momentum and energy are dynamic factors. SD, Cd and tensile strength are static factors. Ask any engineer. Warrior can try to Google it.

By your definition an expanding bullet would be dynamic.
Hence its SD is/canbe dynamic.


SSR

An expanding bullet cannot be dynamic of itself. In any case, how do you read into my post that all the properties of an object are the same as that object? That would be as silly as saying that the colour of the bullet below is dynamic. The colour changes because, when it is recovered after firing, it is not the same as what it was when the bullet was in the box. Does that make the colour dynamic?

color only affects it if you are colored.

In the case of an expanding bullet you are changing considerably more than the color.

How can you be so obstinate as to refuse to see that the expansion of a bullet changes many charateristics. Does a recovered, expanded slug have the same SD as an unfired one?

SSR

.

quote:

So tensile strength could be rewritten as:

Mass x acceleration / area

Hint hint.

Note the change in emphasis. Two static elements and one dynamic element.

Well, from what I've observed, mass and area don't necessarily remain static (unchanging) either. Otherwise, expanding type bullets wouldn't work the way they do, is my guess.*

*I now realize this is wrong. We were talking about tensile strength and that wouldn't change.

Gee whiz, I'm getting confused! I need to quit while I'm behind!

But how do we find the acceleration? (Or in this case the deceleration?) Isn't that due to the drag? And what is the drag? Don't we still use the drag formula of:

F = 1/2 * v^2 * Cd * area (?)

In English units, that reduces down to ft/sec^2, which is the definition of acceleration. (Or deceleration, since it's also part of a resisting force.)
It seems to me that it's inescapable that area doesn't play a part, even if its role is to determine drag.

Otherwise--well, damned if I know.

Alf 9 April 11

quote:

Every time a shooter chooses a bullet to shoot with, whether for hunting, target shooting , self defence or whatever reason he is actually choosing a product that has been willfully manipulated for a specific application of the concept of sectional density ( m/A) through design.

This sounds very familiar. Someone else also talks this talk. Ahhh, here it is:

Warrior 23 Nov 2010
http://forums.accuratereloadin...251016441#7251016441

quote:

We don't walk into a shop and ask for a high SD bullet with a specific number, we do it instinctively based on bullet weight, as being the simplest entity or unit of measure.

Warrior 13 Feb 11
http://forums.accuratereloadin...021001051#9021001051

quote:

SD is relevant in that when you walk into a shop and buy bullets for your 30-06 you consciously make a decision based on SD whether you are going to buy 130 or 150 or 165 or 180 or 200 grain bullets. This decision is based on DISCRIMINATION FOR YOUR INTENDED PURPOSE.

Warrior 2 March 11
http://forums.accuratereloadin...661042151#9661042151

quote:

Now the moment you pick a given bullet weight, you have picked implicitly a SD as well. So, no decision can be made without the SD being involved.

Warrior 17 March 11
http://forums.accuratereloadin...001032251#3001032251

quote:

The moment when you pick one bullet weight over the other, you have discriminated against the other for whatever the reason might be, and that decision rests intrinsically on SD.

Did Alf learn this from the combative one or did he teach Alf?

.

I will unconditionally accept that as the truth and that the combative one got it from you. Thank you for the courtesy.

Cross L,

quote:

By your definition an expanding bullet would be dynamic.

quote:

In the case of an expanding bullet you are changing considerably more than the color.

In my post above is a picture of an expanding bullet. It is also a hollow point bullet and a boat tail bullet. Here is a picture of two solid bullets, fired and unfired.



They are all static objects.

quote:

the expansion of a bullet changes many charateristics

Had you said this in your first post instead of "an expanding bullet", my answer would have been this one below.

A bullet in flight and during penetration and expansion, has dynamic qualities such as speed, energy and momentum. It also has static qualities such as the colour, SD and weight. A bullet that is expanding is subject to dynamic qualities and those qualities cause the bullet to change colour, shape, SD and weight, to name a few. The dynamic qualities change the static qualities - see the post and the reply to someoldguy below.

In a technical discussion, terminology must be precise, otherwise misunderstanding takes place, as we have just seen. No sweat, it often happens that one must backtrack to clarify.

someoldguy,

quote:

Well, from what I've observed, mass and area don't necessarily remain static (unchanging) either.

Mass and area are static qualities that are changed by dynamic qualities. A quality that changes is not always dynamic because a static quality can be changed by the influence of a dynamic quality. (The bridge is imploded or the computer case is crushed.) "Change" and "dynamic" are not always synonyms. An example is: Political change - is it dynamic?

Alf,

quote:

I am in no way fixated on SD alone, my interest and fucus lies in drag, and specifically that effect that drag has on the causation of a wound.

That makes a lot of sense.

Rat Motor

quote:

Did Alf learn this from the combative one or did he teach Alf?

Warrior is incapable of learning or teaching. He repeats mechanically, without comprehension, what he hears or Googles.

OK, would it make everybody feel better if we renamed "dynamic sectional density" as "effective sectional density"? Or do we just get one shot at definitions?

I've been wondering about this:

Suppose you have a 180 grain .308 caliber bullet which impacts at 2000 fps. (It's a mild cartridge. Maybe a .30-30.) We know the sectional density of this bullet is 0.271.

The first time, we shoot the bullet in a conventional rifle.
For the second time, we shoot the bullet in a special firearm and cartridge which is able to shoot this same bullet sideways.

Which bullet is going to penetrate deeper and why?

(Remember, sectional density remains the same.)

quote:

OK, would it make everybody feel better if we renamed "dynamic sectional density" as "effective sectional density"?

No need to rename something that does not exist. There is already a name for it, whatever concept you have of what SD is supposed to have morphed to.

quote:

(Remember, sectional density remains the same.)

There are two ways to look at this.

If SD is calculated with the square bullet method, one could probably say that it stays the same because it is wrong anyway. The sideways bullet penetrates less because the Mo/Xsa has increased and the drag has increased because the shape has changed.

If SD is calculated correctly, the sideways bullet penetrates less because the Mo/Xsa has increased and the drag has increased because the shape has changed.

Either way, SD is irrelevant in this example, whether it is calculated wrongly or correctly. See
the first paragraph after the first picture.

quote:

Originally posted by Gerard:

quote:

OK, would it make everybody feel better if we renamed "dynamic sectional density" as "effective sectional density"?

No need to rename something that does not exist. There is already a name for it, whatever concept you have of what SD is supposed to have morphed to.

quote:

(Remember, sectional density remains the same.)

There are two ways to look at this.

If SD is calculated with the square bullet method, one could probably say that it stays the same because it is wrong anyway. The sideways bullet penetrates less because the Mo/Xsa has increased and the drag has increased because the shape has changed.

If SD is calculated correctly, the sideways bullet penetrates less because the Mo/Xsa has increased and the drag has increased because the shape has changed.

Either way, SD is irrelevant in this example, whether it is calculated wrongly or correctly. See
the first paragraph after the first picture.

So it's drag that's important as one of the factors that resists penetration. That's pretty clear. The sideways bullet will have more drag working against it. But isn't the greater drag due in part to the greater surface area that the sideways bullet would present to the target?

SOG,

Ever notice how gerard gets to assign the meanings? Must be good work if you can get it.

SSR

someoldguy,

someoldguy:

quote:

But isn't the greater drag due in part to the greater surface area that the sideways bullet would present to the target?

Gerard:

quote:

the sideways bullet penetrates less because the Mo/Xsa has increased

Xsa is the surface area.

Cross L,

quote:

Ever notice how gerard gets to assign the meanings?

Get a life. The meanings were assigned long before I even thought about them. Absorb the right material and accept that there are people who know more about a subject than what you do. I do not make up stuff. I am here to discuss, learn and share what I have learned in the last 20 years of manufacturing and designing bullets. If you do not understand what is going on, keep your snide remarks to yourself.

quote:

Now both of you learn manners

You should practise what you preach.

OK, I think I've had more learning than I can stand. Thanks everybody, but I'm done here.