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 posted on the CZ reloading sub-forum, but wanted to get the insight from members here as Ya'll are freakishly smart too and willing to have conversations, rather than just attack each other.

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. 

[The_Shadow]

Well not to get too scientific, I will say that when you drive the heavier expanding bullets faster they tend to open up sooner thus increasing surface area and friction so they may impart more of the energy, actually penetrate less in some medias or tissues.  However the same weight of a non expanding bullet would penetrate deeper, likely more that desired for say self defense where a pass through may strike others.  Even though it would over penetrate doesn't mean it still wouldn't be effective as two holes bleed out faster.

There are only a few things that can put a end stop to the intended target be it a live animal or individual.  Shot placement, and what the projectile encounters as it traverses the body.
Central Nervous System Disruption to shut down the impulses that control any and all muscle function.
Hemorrhagic Shock blood loss, where major arteries, veins or organs, are impacted to cause significant blood loss, this can still take 4-6 minutes for there to be disruption due to O2 levels being depleted in the brain.
Sometimes the impact alone can discourage continued activity...

Now all the science in the world doesn't take all of this into their equations when you push any bullet of a given weight to a particular velocity as it may encounter various forms of hide / clothing / tissues / organs or armor...

What does all of this mean...bullets can be lethal in every size (17- 50 cal etc.), weight so long as the have enough energy to penetrate enough impart damages to what they encounter.  Then you can also think of a tack hammer vs. a sledge hammer...you may ged more velocity from the tack hammer but you can impart more energy with the sledge hammer...

p.s. I knew guys that could destroy an Anvil with a tack hammer! 

[sqlbullet]

The Shadow covers some great points. 

Here is my thought.

Energy is what is in your wallet. Sectional density doesn't really impact it.  Some data from Underwood for 10mm auto:

Bullet Weight	Muzzle Velocity	Muzzle Energy
100 gr	1825 fps	739 lb-ft
115 gr	1700 fps	737 lb-ft
135 gr	1600 fps	767 lb-ft
140 gr	1500 fps	699 lb-ft
150 gr	1500 fps	749 lb-ft
150 gr	1425 fps	676 lb-ft
155 gr	1500 fps	774 lb-ft
165 gr	1400 fps	717 lb-ft
180 gr	1350 fps	728 lb-ft
200 gr	1250 fps	693 lb-ft
220 gr	1200 fps	703 lb-ft

Looking at this data it is pretty clear that the 10mm has an energy budget of about 725 lb-ft of energy regardless of what bullet weight you select.  Yes, lighter bullets exceed this a small amount and heavier bullets run a bit below, but the difference is marginal and generally within the extreme velocity spreads observed in these bullets.

So, we select a cartridge based on the energy requirements of our needs, then we select a bullet based on whether we favor penetration or wound channel.

The nice thing about the 10mm Auto, at least among the common auto-loading cartridges, is it minimizes compromise.  It gives you enough energy budget to select expanding bullets and still retain great penetration.

[Rojo27]

Hey Scarlet,
As you reference and sqlbullet & shadow illustrated; study of ballistics is extremely complex topic. 

I would start by studying Terminal Ballistics:
Terminal ballistics - sub-field of ballistics, is the study of the behavior and effects of a projectile when it hits and transfers its energy into a target. Bullet design (expanding, flat point, fragmenting, solid, frangible to list a few examples) and sectional density as well as mass & velocity (source of the energy) at impact combine to determine the effectiveness. 

Always vital to know the application and the desired outcome. 

I'd recommend you start with a careful read the following:
http://rathcoombe.net/sci-tech/ballistics/methods.html

That should start you on the right track. 

Cheers

[Scarlett Pistol]

Thank you all, this is very helpful. There's so many factors and as sqlbullet points out 10mm minimizes the compromises.

[Scarlett Pistol]

Hey Scarlet,
As you reference and sqlbullet & shadow illustrated; study of ballistics is extremely complex topic. 

I would start by studying Terminal Ballistics:
Terminal ballistics - sub-field of ballistics, is the study of the behavior and effects of a projectile when it hits and transfers its energy into a target. Bullet design (expanding, flat point, fragmenting, solid, frangible to list a few examples) and sectional density as well as mass & velocity (source of the energy) at impact combine to determine the effectiveness. 

Always vital to know the application and the desired outcome. 

I'd recommend you start with a careful read the following:
http://rathcoombe.net/sci-tech/ballistics/methods.html

That should start you on the right track. 

Cheers

I just clicked on the link to start reading... and wow! You spared no expense on providing me an extraordinary piece that gets into all the technical and scientific components. I'll be having a good read for a few nights. Thank you for a great starting point for the extremely technical aspect.

[Graybeard]

One of the members here did some penetration testing using various 10mm bullet types and power levels. The winner was a rather mild 180gr Fmj. Many members thought the 220gr hardcast would take the prize. While the 220 did very well, the lighter and lower energy 180 penetrated deeper due to the smaller meplat. It was a good illustration of how bullet shape is as much a factor as weight and velocity/energy.

[sqlbullet]

W.D.M "Karamojo" Bell favored military FMJ style spitzers when hunting game in africa.  The small frontal area and high velocity ensure deep and straight penetration.  He relied on his proven marksmanship to ensure a fast kill with a bullet to the CNS.

[Graybeard]

Peter Capstick covered that in one of his books. Bell used a .275 Rigby as his back up rifle, on elephants. He dropped some drt on a charge. That's not just excellent marksmanship, there's a set of brass clackers involved, too.

[sqlbullet]

Bell was also a pioneer of aerial dogfighting during WWI.  Assigned as a reconnaissance pilot early in the war he would often leave his observer behind and shoot at the enemy pilots with his hunting rifle.

He definitely had big brass ones, and probably three.