As I use copper bullets SD and penetration are not a determining factor. I have always had enough penetration and mostly right through.

Messor used to say that SD only counts until the bullet deforms, He was able to prove it with math.

A longer bullet shaft usually delivers better penetration. Hardness (resistance to deformation) also plays a big role. 

A longer shaft usually delivers better penetration. Hardness also plays a big role. 

Aaaaiiiiii!

A longer shaft usually delivers better penetration. Hardness also plays a big role. 

Aaaaiiiiii!

Fixed

I don't think SD is a measure of bullet performance.

If you consider all the existing evidence of bullet construction and weight versus velocity versus penetration, then you could get to a conclusion that indicates penetration occurs proportionally to bullet weight, velocity and medium density, until the bullet begins to deform. The greater the bullet deformation, the quicker the velocity drops to zero in the medium.

What is the SD of a muzzle loader ball ? Penetration is usually clean through.

What is the SD of a muzzle loader ball ? Penetration is usually clean through.

In the era of the Brown Bess shoot throughs of more than one enemy soldier in close ranks was far from uncommon.

One also needs to remember that SD probably became important when bullet shapes transferred from long, thin heavy-for calibre bullets of the late 1800's and early 1900's to the modern spitzer-type bullets mostly used today.

Compared to lead bullets it must have been pretty impressive.

What is the SD of a muzzle loader ball ? Penetration is usually clean through.

**********************
But !!!!!!!!!!!!!!!!!!! if that same musket ball was a smaller diameter and weighed the same it would penetrate even further.

In the era of the Brown Bess shoot throughs of more than one enemy soldier in close ranks was far from uncommon.

*************************
Ok, but thats like saying a truck has good penetration because it goes through walls. You are comparing 500 gr object versus 165 gr object - even .223 55 gr goes right through a person.
Nothing in this statement is worth consideration.

One also needs to remember that SD probably became important when bullet shapes transferred from long, thin heavy-for calibre bullets of the late 1800's and early 1900's to the modern spitzer-type bullets mostly used today.

Compared to lead bullets it must have been pretty impressive.

*************************
AGAIN !!!!!!!!!!!!!!!!!! comparisons and comparable.  Surely u would agree that a bullet in 308 with a SD of 400 hitting same media at say 2500 fps as a 110 SD bullet would deform the same and still have greater mass over same frontal area. and penetrate deeper.
PMP Brown box 400 SD
PMP Brown box 110 SD
Both 2500 fps
Both into pure meat - elephant thigh
???? -- would both being same make, design, material etc deform same ?
Same or very similar deformation would still leave the start out 400 Sd with a better after deformation Sd than the 110 start out bullet. 

SD doesn't necessarily equal performance. It only says how the bullet looks, ie how it is constructed out

From AI: "Sectional density in bullets is the ratio of a bullet's weight to its cross-sectional area, which helps determine how well it can penetrate a target."

A lead bullet with exactly the same shape and speed as a cup-and-core or mono bullet will have better sectional density, yet will probably perform worse due to deformation.

If bullets are constructed the same regarding shape and materials, their SD should be the same, irrespective of size. Then mass and speed comes into play.

For a long time, most regular C&C hunting bullets could be compared because their performance was similar due to their construction. It goes out the window once the construction and materials vary.

In the era of the Brown Bess shoot throughs of more than one enemy soldier in close ranks was far from uncommon.
*************************
Ok, but thats like saying a truck has good penetration because it goes through walls. You are comparing 500 gr object versus 165 gr object - even .223 55 gr goes right through a person.
Nothing in this statement is worth consideration.

You sound punchy. I wasn't comparing anything but rather responding to a comment on musket balls. What might be worth considering is that there was epic penetration at very moderate velocity with a low SD number that wouldn't meet the threshold you proposed in your original post. The take away from that consideration could be that SD in an of itself isn't the determining factor of anything.

Perhaps the Treeman should start shooting bullets into some sort of test material and see what happens
Perhaps into trees ?  🙂  😉
There must be some scientific material somewhere showing tests done..
Find out what they did and replicate the test ..
To test ( measure) is to KNOW !

A lead bullet with exactly the same shape and speed as a cup-and-core or mono bullet will have better sectional density, yet will probably perform worse due to deformation.

If bullets are constructed the same regarding shape and materials, their SD should be the same, irrespective of size. Then mass and speed comes into play.

I would hazard a guess that the shape is more important (for optimum performance ) than the SD
You have to hit whatever you are shooting at first ...