I just tried to read that and now my head hurts.

Reloader270

quote:

Is there someone that can explain the use and need for Sectional Density of bullets.

Alf,
SD does not determine how well a bullet may penetrate tissue. That is the problem with the perceptions of SD. Whatever other role SD may have, believing that a higher SD number is 'good' and a lower SD number is somehow 'bad', excluding more important factors, is wrong.

quote:

BC is nothing more than a derived factor that is determined by the ratio of SD to the projectile's form factor ( BC = SD/i)

One can also say that SD is nothing more than a derived factor that is determined by the ratio of the weight/mass of the projectile to a section of the area presented to the direction of movement.

quote:

The SD of a bullet sitting in a box or loaded into the mouth of case has no value,

This is true.

quote:

when you induce motion to that same bullet however SD comes alive

Because it now becomes the ratio of momentum to cross sectional area. Why would you want to call it 'living SD' instead of by the proper name of m/xsa? That just perpetuates the myth of SD somehow being important as a measure of 'goodness' and 'badness'.

quote:

by definition they have to accept that SD is a real entity

Of course SD is a real entity. It is shorthand for a derived factor that is determined by the ratio of the weight/mass of the projectile to a section of the area presented to the direction of movement.

That is the bottom line.

There are a horde of factors more important to penetration and performance of a bullet than the shorthand which is SD.

.

Alf, I agree with you. The science and facts you give around SD is correct. It is just that this is not the perception that the layman has of SD. I use the elements of SD regularly and the shorthand (correctly calculated, not the square bullets one) features in many areas. However, anyone who believes that 'SD determines depth of penetration' is wrong. It does not.

.

don't let the perfect be the enemy of the good

the purpose of mathematics is a decision not a number

Hey guys, Alf is right.

However, once a bullet strikes its target it upsets (unless its a solid). Considering two bullets of the same construction and impact energy but different mass, the low sectional density bullet will upset more thus reducing its penetration because it is moving faster.

A high SD bullet fired in the same gun as a low SD bullet will necessarily penetrate deeper and produce a narrower wound channel because the mushroom formed will be smaller. Its higher mass will ensure penetration even though it starts out slower.

As for the bullet construction having changed the effective laws of ballistics, I'm not so sure - I'm still using some very old design cup and core bullets and looking at the bullets being sold I'd say so are most people.

1. Solids also upset. Good solids upset in a predetermined, controlled manner. Bad solids upset in an uncontrolled, haphazard manner. Construction is the difference.
2. Same construction softs: Increase the speed and the upset increases. Increase the SD and the upset increases. Six of one and half dozen of the other. To increase penetration, the bullet must be constructed differently.

So construction is paramount every time.

quote:

A high SD bullet fired in the same gun as a low SD bullet will necessarily penetrate deeper

See what I mean, Alf.

quote:

However, anyone who believes that 'SD determines depth of penetration' is wrong. It does not.

Ah but it does - all things considered equal.

If you want to play that game and compare a cup and core to a mono you can. Why not compare mono to monp from the same manufacturer but of different calibers.

Now tell me what is wrong with comparing a 130grn 270 mono with a 165 grn .30 cal mono????

quote:

Ah but it does - all things considered equal.

Give me an example.

He just did...but you seem to fail to recognize it.

What many other folks are saying is:

1. Lots of factors impact penetration
2. These include velocity, construction, and materials to name a few.

But also else equal (meaning similar velocity, construction, and materials), Sectional Density is a reasonable metric/index for comparison purposes of the bullets penetration characteristics.


For example:
180 grn .308 has an SD of .271
160 grn .284 has an SD of .283
150 grn .277 has an SD of .279

Therefore all three of these bullet weight/caliber combination will have similar penetration characteristics assuming similar construction, materials, and similar velocities. The 270 being in the middle, 7mm being a little bit better, the 30 caliber a little less and that looking at the SD value is an easy way to do the comparison.

Nobody is disputing the difference between a .308 165 grn round nose solid versus 2700 fps versus a .308 180 grn ballistic tip at 3000 fps

here we go again. 300 gr tsx .458 @2400fps vs 300 gr tsx .375 @2400 fps. which one will penetrate a large animal the best, and why?

quote:

To increase penetration, the bullet must be constructed differently.

That is true under specific conditions but the statement is incomplete. It should read; " .... at the same velocity with the same bullet weight and calibre".

Now what I was saying is that if one were to compare a heavier and lighter bullet fired from the same gun at the same pressure, the heavier one would be slower and would therefore expand less.

If driven to the same impact velocity the expansion would be almost the same (the heavier would expand a trifle more) but the heavier one would penetrate deeper.

With cup and core bullets (and dare I say - with a controlled expansion bullet too) a slower bullet of the same weight will often penetrate deeper than the same bullet fired at higher velocity. That's to do with the higher impact resistance due to its higher velocity and its faster expansion. The wound channel will be larger but closer to the entry point or at least, larger close the entry point.

I did some expansion and penetration tests with identical construction bullets with different SD's and compared 'wound channels' and got some results which illustrate the effect nicely. I'll see if I can find the pics and post them.

And here they are.




The L/H bullet is a 60gr and the R/H a 55gr .224 Hornady Spire Point fired from a hornet at about the same pressure levels. It looks as though the mushroom is about the same although it looks like the 60gr has more retained weight. The second pic shows the test medium in which the lighter and faster bullet clearly dumped more energy in a shorter distance. What is not shown is the actual penetration but I can tell you the slower and heavier bullet had a lot more penetration in that medium. It's waterlogged wool furniture padding packed quite tightly into beer cans opened on the tops. It has very similar characteristics to flesh as indicated by critters being shot. The cans were set in a tube with more of the same medium below and wet but not waterlogged. I did quite a few of those tests. Interestingly, the bullets always came to rest mushroom first (no tumbling).

what about these? .270 tsx 150gr @2850fps vs .308 tsx 150gr @2850fps. med size game. which will penetrait better, and why?

quote:

You can use SD as a relative measure of how bullets of similar construction and similar materials will penetrate across calibers.
For example:
180 grn .308 has an SD of .271
160 grn .284 has an SD of .283
150 grn .277 has an SD of .279

Therefore all three of these bullet weight/caliber combination will have similar penetration characteristics assuming similar construction and similar velocities. The 270 being in the middle, 7mm being a little bit better, the 30 caliber a little less.

Some historical rules of thumb:
SDs of .3 or greater excellent penetration
SDs of .27 reasonably heavy for caliber and very good penetration
SDs of .25 middle weight for caliber
SDs of .226 light for caliber with relatively low penetration compared to other bullet weights in its caliber.

Remember its relative; i.e. a .308 165 grn round nose solid will likely out penetrate a .308 180 grn ballistic tip because of bullet construction.

This is likely a very usable explanation for the reloader.

My comments are for clarification relating to this:

quote:

similar construction and similar materials

Here’s my example between two bullets…
Similar Materials: both are cup and core using lead core and gilded metal jacket
Similar Construction: both are identical shaped non-bonded cup and core flat based soft point spitzer
Same Sectional Density: both are .308 caliber 165gr weight
This data indicates two equally constructed bullets that fully matches the bulk of the discussion in this thread to date and based upon this discussion should give identical within game terminal performance.

Now I’ll throw in a variable that is more important than SD with reference to its performance capability than two identically constructed bullets:
Bullet One: 0.015” jacket thickness
Bullet Two: 0.035” jacket thickness
Again I’ll recount, you’re choosing between two 165gr .308 caliber SP Spitzer bullets, same materials and manner of construction, identical SD and same ballistic coefficient. Which bullet would you use for a 600# elk or perhaps for a 600# bear? Which bullet would you perfer for use on a 20# coyote?


The ‘one thing’ that many are ignoring when discussing the ‘historical rule of thumb’ is that is that that ‘thumb’ presumed that bullets constructed within these SD ranges would use a bullet jacket with sufficient wall thickness for the ‘velocity range’ intended for the bullet and for the ‘intended game’ the bullet is intended for.

There are many issues relating to the construction of a bullet that are more important than the bullets sectional density when identifying the bullets terminal performance capability.

Just my 2¢ on the topic. Flame away as I know a few of you will.

quote:

Originally posted by Gerard:

quote:

Ah but it does - all things considered equal.

Give me an example.

I cannot you are a bullet manufacturer.

The factors that are used to compute ballistic coefficient include the factors for sectional density. That is, you cannot get to the BC without using the sectional density parameters.

You need more physics and less marketing.

quote:

There are many issues relating to the construction of a bullet that are more important than the bullets sectional density when identifying the bullets terminal performance capability.

Only if the sole point of the discussion is hunting. In a non-hunting target application no one cares about your argument.

quote:

1. Solids also upset. Good solids upset in a predetermined, controlled manner. Bad solids upset in an uncontrolled, haphazard manner. Construction is the difference.

Construction???

Awesome thread
Physics is a wonderful thing.
There's lots of physics
There's lots of perceptions of physics
there's lots of simplifications of numbers generated by physics.
There's lots of misapplication of simplified numbers generated by physics .

The right physics applicable to the dynamic at hand describes what happens in results.
I have no criticism of the physics described by Alf.
SD, BC & what happens when a projectile strikes an object are all interrelated chicken & egg perceptions in what an individual hunter thinks about performance( or rather ANTICIPATED performance).
What comes first in your perception determines your perspective.
In the physics, only one comes first
SD !!!!! it drives BC for calibre not the other way round.
The perception of what the SD on the projectile box tells you is the problem.

it drives the BC & tells you the projectile flightpath & terminal velocity vs muzzle velocity drop.
That tells you the impact velocity
at impact the SD changes dynamically depending on bullet construction.
The SD printed on the box tells you 'jack' all about what its SD will be after impact , only its SD before impact.
( this is the "take home" message of what Alf is saying).
In its coarsest sense the SD on the packet tells you that a higher SD number for a similarly constructed bullet in the same calibre can be expected to have higher penetration
But its a coarse comparison.
Typically , big number differences correspond to practical results , but they are influenced by a bunch of variables in their effect such as relative impact velocity & projectile construction affecting the dynamic SD after impact.
using SD printed on a packet as a number for decisionmaking between different brands & types of projectile in penetration after impact is fraught with difficulty in the practical results.
The numbers on the box are the numbers on the box, thats all, they tell you a great deal about the performance of the projectile from the box in air , they don't tell you all you need to know to make a penetration decision.

your knowledge as a hunter & shooter about the construction of the projectile & the type of impact wound you want informs more of your choice about projectile penetration than the numbers on the box.
Use the numbers on the box as your sole decisionmaking at your own peril.
...........it only works as a number comparator of penetration after impact in a very gross sense.


about as much sense as choosing a 25 calibre instead of a 30 calibre to hunt bigger game with bigger heavier projectiles.
The projectile construction selection & where you put it in the end determines more of whether it was a good choice or NOT.

If you want a simple life & simple decisions
go for it with bigger calibres, or bigger projectiles within calibre & bigger SD numbers relative to animal size, for anticipated increased penetration.........its one way of making decisions.
.........just be prepared for some disappointments .
Real life & real physics are more complex.

The devil is always in the detail.

Interesting thread & responses.

quote:

Originally posted by SR4759:

quote:

There are many issues relating to the construction of a bullet that are more important than the bullets sectional density when identifying the bullets terminal performance capability.

Only if the sole point of the discussion is hunting. In a non-hunting target application no one cares about your argument.

And a good day to you...

Apparently you'd prefer a 0.350 SD RN bullet over a 0.350 SD BT Spitzer bullet as well for your target shooting. Feel free, I personally would prefer a bullet more aerodynamic in shape.

quote:

Originally posted by capoward:

quote:

Originally posted by SR4759:

quote:

There are many issues relating to the construction of a bullet that are more important than the bullets sectional density when identifying the bullets terminal performance capability.

Only if the sole point of the discussion is hunting. In a non-hunting target application no one cares about your argument.

And a good day to you...

Apparently you'd prefer a 0.350 SD RN bullet over a 0.350 SD BT Spitzer bullet as well for your target shooting. Feel free, I personally would prefer a bullet more aerodynamic in shape.

Capo,
Apparently your reading comprehension is a little weak. You have it exactly backwards.
I referred to construction not form.

quote:

Originally posted by SR4759:

quote:

Originally posted by capoward:

quote:

Originally posted by SR4759:

quote:

There are many issues relating to the construction of a bullet that are more important than the bullets sectional density when identifying the bullets terminal performance capability.

Only if the sole point of the discussion is hunting. In a non-hunting target application no one cares about your argument.

And a good day to you...

Apparently you'd prefer a 0.350 SD RN bullet over a 0.350 SD BT Spitzer bullet as well for your target shooting. Feel free, I personally would prefer a bullet more aerodynamic in shape.

Capo,
Apparently your reading comprehension is a little weak. You have it exactly backwards.
I referred to construction not form.

SR believe as you will.

Mike,

quote:

He just did...but you seem to fail to recognize it.

I see I have to spell it out. I asked for an example of where, with all things equal, high sd would penetrate better than low sd.

quote:

Sectional Density is a reasonable metric/index for comparison purposes of the bullets penetration characteristics.

See this, Alf, here is another one.

303Guy,

quote:

That is true under specific conditions but the statement is incomplete.

The statement is complete. Adding your modification would turn it to gibberish. Read it again.

quote:

if one were to compare a heavier and lighter bullet fired from the same gun at the same pressure, the heavier one would be slower and would therefore expand less.

Lowering the speed would make it expand less than the faster bullet but, because it is heavier, it will expand more than the lighter one. So the two mechanisms tend to cancel each other out. You confirm this when you say:

quote:

If driven to the same impact velocity the expansion would be almost the same (the heavier would expand a trifle more)

You contradict yourself with:

quote:

a slower bullet of the same weight will often penetrate deeper than the same bullet fired at higher velocity. (with explanation)

Here you say that speed regulates penetration depth despite the sd being the same for both. Mike has said that penetration is determined by: "2. These include velocity, construction, and materials to name a few." Yet you both continue to use sd as the measure by which penetration is judged. Adding 'all else equal' is a false argument because all is never equal when you change weight. Too many other factors also change.

In the photos you show, in support of higher sd resulting in more penetration, you say:

quote:

What is not shown is the actual penetration but I can tell you the slower and heavier bullet had a lot more penetration in that medium.

So connecting sd to better penetration still remains your opinion. There is no illustration of this.

Jim states in his post that construction is the factor that decides penetration. Listen to what he is saying, he is right.

SR4795,
Why would me being a bullet manufacturer prevent you from giving an example? However, you give a good but confusing answer in:

quote:

The factors that are used to compute ballistic coefficient include the factors for sectional density. That is, you cannot get to the BC without using the sectional density parameters.

Confusing, because BC is external ballistics which have little to do with your position on sd/penetration. Good, because you mention the factors for sectional density. I also use the factors for sectional density, together with a number of others, to arrive at many other answers. Sd is sometimes a useful shorthand (I use the correct one, not the square bullet one) so, your comment of more physics and less marketing is somewhat misguided. Sd shorthand can be applied in many ways and penetration depth calculation is not one of them.

quote:

In a non-hunting target application no one cares about your argument.

More confusion, you come on strong for sd and penetration and then make this comment. In fact, in a target application, who cares about penetration depth? Paper is only 80 micron thick.

quote:

Construction???

Yes, construction.

con·struc·tion (kn-strkshn)
As in:
3. The way in which something is built or put together.


DenisB,

Amen.

to bad there is not an icon for mental masturbation

quote:

The statement is complete. Adding your modification would turn it to gibberish. Read it again.

Ah! Yes your statement is indeed complete.

I've made a fair number of bullets myself and fired them into test medium to test for expansion and penetration and each time I get the same result. Penetration with the higher SD bullet is greater unless the velocity is significantly higher. Bullet construction remained essentially the same. However, change the construction i.e. make the bullet harder and penetration increases significantly, depending on the medium.

quote:

You contradict yourself with:
quote:
a slower bullet of the same weight will often penetrate deeper than the same bullet fired at higher velocity. (with explanation)
Here you say that speed regulates penetration depth despite the sd being the same for both.

No contradiction there. I said "will often" and I gave my explanation. In my photo's one can clearly see the difference in damage from the faster bullet. It wasn't possible to record the penetration so I have no choice but to tell what I saw. I didn't really expect anyone to doubt me. Incidently, in the photo of the two bullets, it appears that the slower bullet had more expansion when in fact it had less - it just lost less of its mushroom is all.

Connection SD to penetration is indeed my opinion and unfortunately at the moment I have no illustration. It will also be very difficult for me to set up tests now or I would. At the time I wasn't specifically testing for penetration, it was more of a secondary test. I did need to adjust the catch medium for heavier and slower bullets because of the deeper penetration. That confirms what you are saying. I know that in the world of cast bullets, to get the same penetration and performance, a heavier (higher SD) bullet is indicated. Different construction - again confirming what you are saying.

quote:

Lowering the speed would make it expand less than the faster bullet but, because it is heavier, it will expand more than the lighter one. So the two mechanisms tend to cancel each other out.

On the higher SD bullet expanding more at identical velocity - logic tells me it should but is it noticeable in real life? I have not observed this but then neither have I looked for it.

.

quote:

Sectional density as the mathematical expression of the ratio of a body's mass to it's presenting surface area in the direction of motion of that body is integral and obligatory to our understanding of drag force as felt by that body when moving in a medium.

I have a stupid question ALF:

When you say 'presenting surface area' and if we imagine a bullet in flight, is the surface area only the very tip of the bullet (that part which intersects a plane perpendicular to the path of the bullet), or does it take into account everything you would be able to see (the full diameter) if you were able to look directly at the bullet as it traveled towards you?

quote:

Originally posted by Reloader270:
Is there someone that can explain the use and need for Sectional Density of bullets.

all I will say is that;

you can have a bullet with high SD....and a bullet[same cal.] that has a lower SD,

However, depending on the material[s] used and bullet design/construction, the lower[out of the box] Sd bullet may infact end up penetrating further than the initially higher Sd bullet, in live tissue.

A bullets Sd and/or retained weight can change/vary whilst on its path through the animal and commonly does ....some bullets much more than others.

Comparing two hunting bullets on how they behave & perform in artificial test media like wet pack,water jugs or ballistic gel,[or how many trees they penetrate after going through a live animal], can have little or no relevance to comparative bullet performance in live game.

Sd based measure of performance/behaviour of a bullet that can often be called apon to penetrate other natural or man-made obstacles [before reaching the primary living target], does have value, but does not much apply to the hunting or culling of wild animals, where the bullet usually does not encounter any foreign solid material interference before contacting the live target animal.


I other words If one has to penetrate armour,glass,metal,wood,masonry,cloth, etc- barriers before being able to effectively kill/sufficiently penetrate the intended target beyond it, then bullet Sd whilst penetrating through such materials[to target] is of consequence.....but of little consequence in the general recreational hunting world.

Manufacturers may choose projectile materials like tungsten carbide core to increase weight & improve density..and choose certain nose geometry, ..in order to restrict loss of mass & momentum and restrict deformation/mushroom/parrachute effect,..thus improving penetration.

Mike,

quote:

to bad there is not an icon for mental masturbation

It did not take long for logic to run out and insult to take it's place, I see. Now we know to take your your further input and ignore it. Thanks.

Alf,
I agree with most of what you say, the science is good for the most. Some of the conclusions are not applicable in practise, though.

BaxterB,
That is not such a stupid question. It puts several things in a nutshell.

Trax underlines the fact that bullet penetration is far from simplistic. Stating that a bullet will penetrate better because it has higher sd numbers than another is as silly as saying one will penetrate better than another because it is faster/slower/fatter/thinner or a nicer color. Penetration cannot be determined by a single factor.

quote:

Considering two bullets of the same construction and impact energy but different mass, the low sectional density bullet will upset more

Ah, I doubt anyone would disagree with that statement. But therein lies the crux of the matter; bullets of the same weight and diameter have exactly the same SD but those of different design DO NOT have the "same construction" so agonising over Sectional Density has no valid justification today, it tells the gunner nothing helpful. Fact is, the SD of a bullet is exactly the same if it's loose in my pocket or flying at 5,000 fps. Injecting effects of velocity or Ballistic Coefficent, etc, into the VERY simple Sectional Density formula - which ONLY considers weight and cross-sectional area, while excluding velocity or form factor - is pointless belly button contemplation; ditto bringing up projectles flying sideways or as fragments. None of that stuff finds relivant application in the very simplistic ballistic principle of Sectional Density as it applies to modern bullets so the whole premise of arguing otherwise is too flawed to bother with - and that's not personal, it's fact.

It's hard to take an argument without sound basis very serious, SD is simply no longer relivant so I'm surprised this thread is still active. "All things being equal except 'x'... " discussions can be interesting mental gymnastics for some folk but the fact that things are usually NOT equal voids the whole thing, and certainly so for SD.

33 projectile types , same calibre, typical velocity at 100M for projectile weight, wet pack media average of 3 tests per result.
SD in bold
penetrations below in inches.
( each penetration listed for a different projectile type/manufacturer with the same SD)

0.174
9.0

0.184
10.17

0.195
6.25

0.205
16.67

0.246
10.3/11.17/13.67/14.42/15.17/17.2

0.256
10.17/15.0

0.264-0.266
13.08/13.3/15.0/18.0

0.287-0.291
12.17(3)/13.0/13.25/13.75/13.8/14.17/14.25/14.3/15.17/16.5

0.328+/-
12.8/13.7(2)/13.9/14.67/14.92

Obviously there is a VERY general correlation of penetration increasing with SD
But the spread of penetration results indicates pretty obviously that there is something else determining penetration at average velocity for the projectile size.( its called construction)
typical of hunting loads the velocity decreases with projectile weight.
( no correspondence will be entered into to the question "what would the results look like if the velocity was constant".........we are talking typical hunting velocities for the projectile weight as occurs in hunting in real life )
What also is obvious is that a projectile with an SD of 0.205 & another at 0.246 had the second and third highest penetrations in the whole series and greater than the results from the heaviest projectiles with the highest SD in the calibre.
No correspondence shall be entered into about what construction these 33 individual projectiles brands & types were ( 99 individual tests).
This thread is about S.D and what it supposedly tells you about penetration as the thread developed.

Bottom line ........choose your projectile for penetration based on SD alone at your own risk.

As an aside,
one of projectiles in the second highest SD class with the highest BC of all of the projectiles produced the lowest penetration in the class and only 6 of the projectiles out of the 33 types produced a lower penetration

ie
it might fly straight & true but it didn't do great stuff when it got there as penetration.
Its SD & BC were very poor predictors of penetration.

Haven't the time nor inclination to tabulate & correlate the frontal surface area of the expanded projectiles when they came to rest in relation to the dynamic change in SD after impact & its correlation to penetration.
The series of final frontal area & retained weight results does demonstrate the dynamic that Alf described quite well tho.....He He

Not my tests.........I'm just the stupid idiot who wasted a couple hours of his life collating the available data from the test series
Kudos to the gentleman who laboriously did the 99 individual penetration tests.

.

Alf,
Someone must tell these guys that ballistics is stochastic. I am sure they do not know. http://www.army-technology.com/projects/g6/

I see you coin a new term: 'Dynamic SD'.

Why not just call it by its proper name, that has been around for yonks and is understood by all? There is no need to call water dihydrogen monoxide just for the sake of confusion. Prank, yes, seriously, no.

PS. Maybe a 6.5 Carcano is stochastic?

`

Where did you first come across it? I have never seen it, other than used by yourself and Warrior.

Agree that SD of a projectile is dynamic at every stage of its path from muzzle to where it stops.
The dynamic change in SD in flight in air is relatively small as its the frontal area parameter that is changing in flight from change in orientation to flightpath, while mass remains constant.

The SD of a rifle bullet changes very dramatically after impact between impact & coming to rest, as most projectiles undergo loss of mass after impact and a substantial increase in frontal area , with the most change occurring in a short distance after impact.

Common situations with a cup & core projectile are:-
- loss in mass - 30% ( range 0-90% ...all types)

- increase in frontal area - 400% ( range 50-900% all types)

- with a total SD change ,in the common example above, being a reduction in SD to around 20% of what it was immediately before impact.
ie
a projectile that has retained 70% of its weight & mushroomed to twice its original diameter at impact has reduced its SD to 20%( approx) of what was written on the box.

That sure is pretty dynamic change.
many hunting bullet designs undergo much higher reduction in SD than that , after impact.

Those DG types designed to maximise penetration losing very little weight & increasing frontal area very little either, to maximise retained SD and minimise drag.

BTW........there were no DG type bullets in the test data I reported above........all of those reported were designed to mushroom to varying degrees on impact ( typical general purpose hunting bullets).

.

quote:

Yes, construction.

con·struc·tion (kn-strkshn)
As in:
3. The way in which something is built or put together.

Tell us how solids are constucted differently?
You are talking about machined features not about construction. All you can do is take material off of the out side or drill axial holes.... and then try to fake it like it is contruction.

Let's see by some theories a bullet with a high BC and zero SD would be ok as long as properly constructed?

Folks, just bear in mind this is a very interesting and informative thread! Why is the thread still going? Because there are so many variables and unknowns which are being highlighted in this thread that we are interested in. Bullet performance and selection is complicated (I solved that problem by going heavy and slow with cup 'n core bullets on the one hand and the same with cast). For me listening to the mathematician go into theory on the one hand and the bullet maker going into practical application of bullet design is very helpful in gaining an understanding of what I've wondered about for a long time.

Thanks for your input, DenisB. Very interesting when tied in what others have been saying.

P.S. Gerard, I'm currently flatting with a family of ex PE folks and one Kiwi girl.