SECTIONAL DENSITY

Hello everyone,
quick question, i am a bit confused regards bullets sectional density, can someone clarify if a hi sectional density is more desirable than a low or vice versa?
I been comparing the numbers at the Hornady 6.5cal projectiles such as Amax(140gn, S/D= 287), SST(140gn, S/D= 287), ELD-M(140gn, S/D= 287) and ELD-X(143gn, S/D= 293) and other than bullet construction what would make the so call "Match" bullets not to be "desirable/recommended/considered" for hunting(medium to large game)?

Thank you in advance.

Mac

you have answered your own question Mate...... bullet contruction is the reason, some match bullets are too thin in the jacket (ironically this can make them ideal at long range/lowervelocity) others have too thick of jacket making pinhole wounding a real probability. Nathan Foster goes into this in detail on his website Terminal Ballistics.
short answer id higher SD should penertrate further/be harder to stop..... eg an arrow will pass through a sandbag.

Construction with a view to destruction. The match bullets are not designed to spread apart but stay somewhat in tact to create a lovely wound channel. The target versions just zip on through and may even tend to rely on contact with bone to cause much in the way of deformation. Having said that, I've tried the 140gn eldm on a hare and it made a baseball sized exit wound (after hitting the spine)

Still waiting on those 147gn eldm to arrive....

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Originally Posted by Dead is better

Construction with a view to destruction. The match bullets are not designed to spread apart but stay somewhat in tact to create a lovely wound channel. The target versions just zip on through and may even tend to rely on contact with bone to cause much in the way of deformation. Having said that, I've tried the 140gn eldm on a hare and it made a baseball sized exit wound (after hitting the spine)

Still waiting on those 147gn eldm to arrive....

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Probabaly more a case of hydrostatic shock in this instance rather than projectile design, assuming the hare wasn't miles away and there was still high residual velocity.

Basically the heavier a bullet is for its caliber the higher the SD will be. So a 140gr .264 cal bullet will have a higher SD than a 140gr .284 cal bullet.

As mentioned above, generally the higher SD bullet is more likely to penetrate further, however the construction and how frangible the bullet is also plays a part on how much it will expand and penetrate.

This is why many favour 6.5mm and 7mm calibers, as they sit in a nice sweet spot of quite high SD's and BC's for their bullet weights.

Thank you guys, i appreciate your feedback. Yes, i understand the different construction but saying it and considering(what i think is the deformation factor(S/D)) i keep thinking that whatever is the suggested "purpose" these bullets should work similar.
Anyway, follow a photo a rabbit shot at 50mts and a out of focus damage on a goat shot at 675mts. in the goat case the bullet went through but the lungs was split in two.
Handled 140gn Hornady eld-m.


Attachment 64208

Attachment 64209
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He was 100m tops. Kinda felt bad to blow him up so bad as i was intending to either eat him or donate him to somebody with a dog. He became hawk food instead (sigh)
p.s i was just gunna link this but i was just inspired by PERRISCICABA above

Attachment 64214

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Originally Posted by GWH

Basically the heavier a bullet is for its caliber the higher the SD will be. So a 140gr .264 cal bullet will have a higher SD than a 140gr .284 cal bullet.

As mentioned above, generally the higher SD bullet is more likely to penetrate further, however the construction and how frangible the bullet is also plays a part on how much it will expand and penetrate.

This is why many favour 6.5mm and 7mm calibers, as they sit in a nice sweet spot of quite high SD's and BC's for their bullet weights.

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Hey @GWH, thank you for the reply, the "S/D" i am talking about is "Sectional Density" and not "Standard Deviation"…

Cheers man!

Mac

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Originally Posted by PERRISCICABA

Hey @GWH, thank you for the reply, the "S/D" i am talking about is "Sectional Density" and not "Standard Deviation"…

Cheers man!

Mac

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Yep realize that 😉

Sent from my SM-G900I using Tapatalk

A good example of SD is the 160 grain 6.5 Hornady RN at .328 you have to go to the 220 grain .30 Hornady RN at .331 to beat it, I know which one I'd rather shoot,
Depends on your application which you choose for big game high SD is desirable for deep penetration, for varmints low SD and high velocity thin jackets give low penetration
and quick expansion, The Hornady 160 RN is still a good choice for 200 metre deer shots if you know the drop.

SD = M/A

SD is the sectional density
M is the mass of the projectile
A is the cross-sectional area

Sectional density is the ratio of an object's mass to its cross-sectional area with respect to a given axis. It conveys how well an object's mass is distributed (by its shape) to overcome resistance along that axis. For illustration, a nail can penetrate a target medium with its pointy end first with less force than a coin of the same mass lying flat on the target medium.

Good old Wiki :D

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Sectional Density - A Practical Joke?
Terminal performance is a highly complex subject and an interaction of a multitude of factors. The closest one could probably come to a single factor for gauging terminal performance, is Momentum/Cross Sectional Area (Mo/XSA) and then only if the numbers are tempered with bullet shape, bullet construction and the effect of speed induced stagnation pressure.

The bottom line is that, choosing between two bullets based purely on sectional density, is as foolish as choosing a bullet based on the colour of the packaging.

Gerard Schultz

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I will post a link to the relevant article next.

http://www.gsgroup.co.za/articlesd.html
Mr Schultz has a lovely sense of humour.

1. Animals fall down reliably if a vital organ is destroyed, regardless of sectional density of the bullet.

2. Animals fall down reliably if the bullet retains enough weight and has enough speed to penetrate to a vital organ regardless of sectional density. This is interesting, weight and speed are the factors that determine momentum and energy values.

3. The sectional density value seems to be of no importance at all, providing it did not disappear completely.

4. The post impact sectional density of a bullet is almost always less than the starting sectional density.

This leaves only one question unanswered. Who first came up with the theory of sectional density? Was it some ballistician with a macabre sense of humour? Did he put forward this theory as a joke and it got out of control? Sectional density seems to be the ballistic equivalent of an internet chain letter. No matter how illogical or outdated or disproved it is, it keeps on popping up. Almost like the concept of hydrostatic shock, but that is another story.

To your success,

Gerard Schultz

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Originally Posted by JWB

Sectional Density - A Practical Joke?
Terminal performance is a highly complex subject and an interaction of a multitude of factors. The closest one could probably come to a single factor for gauging terminal performance, is Momentum/Cross Sectional Area (Mo/XSA) and then only if the numbers are tempered with bullet shape, bullet construction and the effect of speed induced stagnation pressure.

The bottom line is that, choosing between two bullets based purely on sectional density, is as foolish as choosing a bullet based on the colour of the packaging.

Gerard Schultz

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Well no more than E=mc2 is a joke?

As professor @Gibo said SD = M/A so we are only missing velocity as the final factor to form Gerard Schultz's magic Mo/XSA which is limited by how much powder you can get behind the bullet and the length of your barrel. :P

Obviously bullet construction has a significant impact on how the bullet reacts on impact but SD will affect bullet penetration.

You can only compare the sd of bullet of the same construction, shape , and material and material hardness .

A soft lead bullet of the same general shape and weight / caliber as its jacketed hard lead counterpart might behave differently :
-in the air regarding its ballistic trajectory
- in an animal regarding its terminal ballistics .

And again a copper or brass turned bullet will behave deferently from a depleted uranium projectile

Ok, I apologise if I start a discussion that may not take us anywhere. Why I did ask is because "I" understood that Sectional Density had something to do with how easily or hardly a projectile will "expand" under certain condition.

I can see that we are going for a long discussion and it is not what I was meaning, I just like to understand all about the "fussy" about projectiles

Thank you for all of you guys who spent the time sharing the information I appreciate it. If you guys think it is a good "cause" to discuss I will be all "eyes and ears"

Cheers

Mac

SD was dismissed in the 1940s

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Originally Posted by zimmer

1. Animals fall down reliably if a vital organ is destroyed, regardless of sectional density of the bullet.

But I prefer using something like lead copper or even depleted uranium to plastic or wood... Why? Because it's more likely to achieve the desired vital organ destruction..

2. Animals fall down reliably if the bullet retains enough weight and has enough speed to penetrate to a vital organ regardless of sectional density. This is interesting, weight and speed are the factors that determine momentum and energy values.

So my favorite 150 grain .308 projectiles will work just as well if they were the size of a football (and weighed the same 150 grains)? Retaining enough weight and has enough speed to penetrate to a vital organ is only possible if the projectile has sufficient SD.

3. The sectional density value seems to be of no importance at all, providing it did not disappear completely.

OK so anything heavier than air will do?

4. The post impact sectional density of a bullet is almost always less than the starting sectional density.

?

This leaves only one question unanswered. Who first came up with the theory of sectional density? Some idiot that decided it was better to use lead instead of stones for musket balls Was it some ballistician with a macabre sense of humour? No but the Military seem to like it https://en.wikipedia.org/wiki/GBU-28 Did he put forward this theory as a joke and it got out of control? No it's physics. Sectional density seems to be the ballistic equivalent of an internet chain letter. No it's physics. No matter how illogical or outdated or disproved it is, it keeps on popping up. Maybe for a reason?Almost like the concept of hydrostatic shock, but that is another story.

To your success,

With VERY LOW SD bullets... Yeah right.

Gerard Schultz

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OK so I am bored BUT this guy obviously missed 5th form physics!

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Originally Posted by PERRISCICABA

Ok, I apologise if I start a discussion that may not take us anywhere. Why I did ask is because "I" understood that Sectional Density had something to do with how easily or hardly a projectile will "expand" under certain condition.

I can see that we are going for a long discussion and it is not what I was meaning, I just like to understand all about the "fussy" about projectiles

Thank you for all of you guys who spent the time sharing the information I appreciate it. If you guys think it is a good "cause" to discuss I will be all "eyes and ears"

Cheers

Mac

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Mac , amax , eld m and eld x all kill :D you are most welcome ;)

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Originally Posted by PERRISCICABA

Ok, I apologise if I start a discussion that may not take us anywhere. Why I did ask is because "I" understood that Sectional Density had something to do with how easily or hardly a projectile will "expand" under certain condition.

I can see that we are going for a long discussion and it is not what I was meaning, I just like to understand all about the "fussy" about projectiles

Thank you for all of you guys who spent the time sharing the information I appreciate it. If you guys think it is a good "cause" to discuss I will be all "eyes and ears"

Cheers

Mac

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Haha that was at least 10 min of entertainment on an otherwise boring Tuesday.

Not to flog a dead horse but SD is important but it is only part of the picture (in that it doesn't have regard to velocity), and even then, it is only relevant to pure penetration (making it a lot more relevant to larger game).

What determines the penetrative ability of a projectile in a medium (animal), is the Kinetic Energy Density (KED) of the round. KED is the Kinetic Energy (in Joules) of the round (1/2 * Mass (in grams) * Velocity ^ 2 (in m/s)) divided by the cross sectional area of the round (in m^2).

Therefore to increase penetration, either make the round go faster and/or increase the sectional density (by increasing mass and/or decreasing cross sectional area).

But penetration is only part of the what you are after when poking holes in animals. You ideally want all of that Kinetic Energy to couple (be transferred) to the target as that is what causes damage due to the deceleration of the round, and if you get too much penetration (too high KED) then that full transfer doesn't occur and it just makes a pencil hole. That's where things like actual round construction and shot placement come into it. They (particularly round construction) will determine how and whether a round expands inside a target

Lentle n Saxton put it rather well , I will see if I can convey thier meaning without cocking it up to much
take the .30/06 for eg on paper the 110grn pill going super fast has shot loads of energy so should kill well...this is a bunch of bollocks its energy will explode projectile and create wide shallow wound
the 220 grn pill in same rifle on paper is mild by comparison yet will penertrate VERY well and kill animals effectively

thats gist of what they wrote
now if you put a barnes type 110grn pill in the 06 it will kill very well out to say 250 yards as pill is hard enough to handle the speed yet expands enough to create wound channel
also if you take the 220 grn eg and feed rifle a pill designed for a super hot 300 magnum it will pencil through BUT if you used a AMAX/eld type or even a soft conventional type like speer make well it will shed some weight and deform somewhat therefore creating wide enough wound channel and transphering some energy.

so bullet construction IS VERY IMPORTANT sure we have all killed/seen killed animals with FMJ .303 ammo but if we didnt hit bone it wasnt pretty or fast as they zipped on through.

feed that 06 with the likes of a 180grn SST and you wont be far wrong on any account.
ive loaded the 06 with 125-130-150 grn loads for recoil sensitive mate and he never had issues taking animals down,the lightweight pills were used on goats and would decapitate with high neck shot at close range.

Penetration does not neccessaraly kill. I have witnessed that a few times and penetration of the same 220 gr as the 30-06 above at sub speed is vastly superior to what is does at supersonic speed. The bullet just does not expend and loose very little energy.