Help With Ballistics Science/Physics

[Scarlett Pistol]

I need a little help/direction on what to go read/learn for a more comprehensive understanding of ballistics. I'm posting here because ya'll are very intelligent and willing to have civil discussions.

This stems from people arguing over penetration. You know, weight means greater penetration vs energy....

I am reading on the details of sectional density, which seems to be the equation that helps put weight in perspective to specific bullet diameters and then penetration.

BUT - In the equation for energy, velocity is squared.

I am not trying to spark an argument on one vs the other. I am hoping to get direction on how these interact with one another. Weight means a sacrifice in velocity, which really impacts energy -- but in turn increases sectional density. Thereby, Supposedly increasing penetration? Why would that be the case? What parts/equations/principles of physics am I missing in this whole system to really understand this interaction?

I'll happily take explanations, references to articles, tests, even books. I understand this is complex and I will put in the reading and study if you tell me where to get the content. I'm just getting tired of hearing opinions and sales pitches. I want to really be able to sift through the science of this myself. Thank you for any and all help!

Again, I am not trying to spark arguments between the concepts. If there is disagreement let's all figure out the physics and be willing to really consider all aspects. "My Grandpa shot a F***ING Elephant with a 45 ACP and it penetrated the skull, so weight beats velocity!!!! Fight me if you disagree." Sort of anecdotes (while fun to hear) aren't the point of this and won't help me or us have this discussion. 

[Crawl]

From:

Applied Ballistics for Long-Range Shooting by Bryan Litz

A couple of examples of a book that might not explain it as thoroughly as you'd like, but there are lots of charts and data regarding range, velocity, and mass.

[Tok36]

Tag.

[Hammer Time]

People have been trying to simplify ballistics (and sometimes extending that to make simplistic assumptions about the attributes of various calibers...) for a long time. But the bottom line is that it's really complicated. Velocity and mass are two of the fundamental factors, for sure. But if you're evaluating based on penetration, then a host of other factors come into play as well, such as - what exactly is being penetrated? Ballistics gel? An obese person wearing four layers of winter clothing? An elk chest cavity? Or a physical barrier of some sort? Factors that contribute to good penetration in one of those examples don't necessarily equate to good penetration in the others, by any means.

I think there are basics principles of physics that apply, but if you want to take it out of the classroom and into the real world, then you really have to pay attention to so many different variables that it either becomes a really expensive and broad experiment, or by necessity it becomes focused on specific platforms, calibers, etc. for which the results are particularly relevant for you.

I realize that's not helpful for coming up with simple and straightforward answers, but honestly, I'm just not convinced there are simple answers, as much as we may yearn for them.

[copemech]

You see, if you hit something really hard, it will hurt you more than it hurts it!

At least that's what my dad used to say!

[Scarlett Pistol]

From:

Applied Ballistics for Long-Range Shooting by Bryan Litz

A couple of examples of a book that might not explain it as thoroughly as you'd like, but there are lots of charts and data regarding range, velocity, and mass.

Thanks Crawl, that definitely helps.

People have been trying to simplify ballistics (and sometimes extending that to make simplistic assumptions about the attributes of various calibers...) for a long time. But the bottom line is that it's really complicated. Velocity and mass are two of the fundamental factors, for sure. But if you're evaluating based on penetration, then a host of other factors come into play as well, such as - what exactly is being penetrated? Ballistics gel? An obese person wearing four layers of winter clothing? An elk chest cavity? Or a physical barrier of some sort? Factors that contribute to good penetration in one of those examples doesn't necessarily equate to good penetration in the others, by any means.

I think there are basics principles of physics that apply, but if you want to take it out of the classroom and into the real world, then you really have to pay attention to a so many different variables that it either becomes a really expensive and broad experiment, or by necessity it becomes focused on specific platforms, calibers, etc. for which the results are particularly relevant for you.

I realize that's not helpful for coming up with simple and straightforward answers, but honestly, I'm just not convinced there are simple answers, as much as we may yearn for them.

I agree, and I think the desire to simplify something very complex has led to more confusion. I definitely want to be directed to the full coverage of the subject, no matter how complex.

What led me to do more research on this concept this time around was this video:
https://youtu.be/9KvNGMME_Bc

And Carl (Karl?) says he tends to agree that heavier bullets will hit hard. Maybe they do... but I had the thought that a 9mm bullet that heavy is going to be moving awfully slow and thereby it will suffer a big lose in its energy, so does it really hit that hard? Now that I am reading more I can say that it will have a fantastic Sectional Density because it is so heavy for it's diameter. But if it has sacrificed so much in energy is the weight worth it? It can't capitalize on that Sectional Density potential. Especially because it is a hollow point and once it hits flesh and expands the Sectional Density will change (decrease) as it expands and also dumps that energy (which has been sacrificed for weight).

I'm not trying to argue that heavier bullets aren't that great. We see a swing in the opposite direction with 9mm bullets that we super light and screaming fast. Their sectional density sucks, but their energy is high because they have ramped up velocity. The gain in energy at the sacrifice of weight.

I'm getting to some videos on ballistic coefficient. Is there a ballistic coefficient (or concept like it) for Terminal Ballistics? The bullet shape obviously plays a role in penetration (hollow points expand and penetrate less and vice versa). 

Maybe I am typing myself in circles in the middle of a learning process. I am just trying to piece together how high energy lighter bullets don't seem to perform as well as heavier bullets even though they have more energy. Sectional Density doesn't seem to explain it entirely because it seems like a function of potential that would then rely on energy imparted on the object (bullet) and some other factors.

[Scarlett Pistol]

On the 10mm forum a gentleman referenced me to this article.

http://rathcoombe.net/sci-tech/ballistics/methods.html

I think it will help me get a better understanding of the physics going on here.

[Crawl]

From the external ballistics side, I think chapter 15 of "Applied Ballistics for Long-Range Shooting" gets to your point.

Litz recommends reading "Rifle Bullets for the Hunter" for a definitive study of terminal bullet performance.

Litz discusses lethality saying:

"Velocity ays a very important role...but there's much more to it."

"...hydrostatic shock is very damaging"

"The strength of the shock is proportional to the velocity of the bullet. Impact velocity alone won't necessarily be lethal if the bullet is quickly stopped a short distance inside the animal."

"This is where penetration comes in. If the bullet strikes with sufficient velocity and has significant mass to retain the velocity as it penetrates, then the bullet can generate a significant hydrostatic shock that incapacitates the animal...[this] is what makes it more lethal than an arrow."

He goes on to discuss Kinetic Energy (KE) and Momentum.

KE=1/2mVV

Momentum=mV

"KE is influenced by mass and even more so by velocity...KE is an indicator of the peak level of hydrostatic shock the bullet can achieve on impact."

"Momentum is equally affected by mass and velocity...momentum is related to the bullet's ability to maintain velocity and a high level of hydrostatic shock as it penetrates through an animal."

The chapter goes on to discuss lethality from the point of view of KE and momentum. It points out formulas, such as the Optical Game Weight Formula, to help select bullets for certain applications.

After all of this, I still haven't seen anything that describes where the tradeoff is, but I think the answer lies somewhere in charting momentum and KE for various cartridges all on one chart. Of course bullet selection matters (i.e. hollow points create more shock because they transfer more energy to the target).

[Scarlett Pistol]

From the external ballistics side, I think chapter 15 of "Applied Ballistics for Long-Range Shooting" gets to your point.

Litz recommends reading "Rifle Bullets for the Hunter" for a definitive study of terminal bullet performance.

Litz discusses lethality saying:

"Velocity ays a very important role...but there's much more to it."

"...hydrostatic shock is very damaging"

"The strength of the shock is proportional to the velocity of the bullet. Impact velocity alone won't necessarily be lethal if the bullet is quickly stopped a short distance inside the animal."

"This is where penetration comes in. If the bullet strikes with sufficient velocity and has significant mass to retain the velocity as it penetrates, then the bullet can generate a significant hydrostatic shock that incapacitates the animal...[this] is what makes it more lethal than an arrow."

He goes on to discuss Kinetic Energy (KE) and Momentum.

KE=1/2mVV

Momentum=mV

"KE is influenced by mass and even more so by velocity...KE is an indicator of the peak level of hydrostatic shock the bullet can achieve on impact."

"Momentum is equally affected by mass and velocity...momentum is related to the bullet's ability to maintain velocity and a high level of hydrostatic shock as it penetrates through an animal."

The chapter goes on to discuss lethality from the point of view of KE and momentum. It points out formulas, such as the Optical Game Weight Formula, to help select bullets for certain applications.

After all of this, I still haven't seen anything that describes where the tradeoff is, but I think the answer lies somewhere in charting momentum and KE for various cartridges all on one chart. Of course bullet selection matters (i.e. hollow points create more shock because they transfer more energy to the target).

Crawl, if you go read that link I posted it comes together. It's the balance of cavitation and penetration. He starts out with flat nose pistol bullets and had these two equations that predicted bullet performance very well. He states almost exactly what you are quoting as he explains how these concepts work.


Penetration (in wetpack):
PEN(FN) (inches) = Bullet Weight (lbs) x Impact Velocity (fps) / Meplat Diameter (inches) / 5

Cavitation (in soft tissue):
CAV(FN) (inches) = Impact Velocity (fps) x Meplat Diameter (inches) / 225 - 0.725

He has examples of performance from animals on hunts with such bullets to see how the models perform in real world usage.

He also goes on to say,

In these empirically-based expressions for flat-nosed bullets, penetration is seen to be a function of momentum and represented diameter, while cavitation is a function of velocity and represented diameter; these tend to agree with common sense as well. If you multiply these two formulas together you obtain a relationship (discounting the constants) with the units of energy, which agrees with terminal ballistic theory in that wound volume should be proportional to kinetic energy (observe that cavitation may be equivalently expressed as specific energy times unit area).

I'm still reading through the sections with expanding bullets, but this is helping explain these relationships

[Crawl]

Fantastic information! The correlation graphs are quite compelling.

Have you come up a way to determine how, for a given cartridge, to chart the penetration potential based on varying amounts of mass and velocity? I'd like to think that with the right dataset, one could determine the ideal kinetic energy and/or momentum (mass and velocity) for a given cartridge in order to maximize penetration.

Of course, this disregards all of the disadvantages to maximizing energy.

Then, it makes me wonder which of those have the most impact on recoil...

[painter]

Mass and velocity are the sole factors affecting recoil.

[Joe L]

There is a reason I shoot paper. 

(Engineer) Joe

[copemech]

Mass and velocity are the sole factors affecting recoil.

There is also wait!

[painter]

Mass and velocity are the sole factors affecting recoil.

There is also wait!

Wait (weight  ) is mass in this context.

[copemech]

Mass and velocity are the sole factors affecting recoil.

There is also wait!

Wait (weight  ) is mass in this context.

no, no, no, it is how long you gotta wait till it hits something!