Thread: SECTIONAL DENSITY

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 No matter how illogical or outdated or disproved it is, it keeps on popping up.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 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

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

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.