Thread: 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....

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....

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.

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

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.

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

Cheers man!

Mac

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

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

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

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

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

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.

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