Is there any correlation between momentum and penetration / terminal ballistics?

simonrichter · November 28, 2018, 02:55 AM

I was just wandering how bullet momentum (velocity x weight, thus not weighing in velocity(2) like energy) influences terminal performance?

collector rob · November 28, 2018, 05:16 AM

Good read from the Box o' Truth.

https://www.theboxotruth.com/the-box...e-box-o-truth/

jmr40 · November 28, 2018, 04:04 PM

No. Momentum is a good way to predict which rounds will more reliably knock over steel plates, bowling pins or other heavy objects.

The best way to predict penetration, all things being equal, is bullet length in relation to weight. Longer bullets tend to be heavier in the same caliber, but when comparing bullets of different calibers things get interesting and harder to predict.

Of course bullet construction and velocity are factors too. That is why I said "all things being equal" above. All bullets are designed to work best and expand well within a range of impact speeds. Too fast and they over expand and don't penetrate. Too slow and they may not expand.

It is far from an exact science, but momentum is a poor way to judge bullets effectiveness.

themalicious0ne · November 28, 2018, 05:41 PM

It depends on the medium and the amount of necessary penetration.

For instance, if you were shooting at a bear with a handgun, a bullet with greater mass and momentum would probably be preferred for more penetration compared to one with less mass and momentum, even if they had the same KE. There are an unlimited amount of variables, a 22lr will penetrate Kevlar easier than a 45acp.

Momentum will have an effect but it really just depends on the application and what you are comparing.

jfruser · November 29, 2018, 10:46 AM

Quote:

Originally Posted by simonrichter

I was just wandering how bullet momentum (velocity x weight, thus not weighing in velocity(2) like energy) influences terminal performance?

Momentum is better-correlated to penetration than is kinetic energy, which squares the velocity.

But momentum alone is lacking a factor...

Quote:

Originally Posted by jmr40

No. Momentum is a good way to predict which rounds will more reliably knock over steel plates, bowling pins or other heavy objects.

The best way to predict penetration, all things being equal, is bullet length in relation to weight. Longer bullets tend to be heavier in the same caliber, but when comparing bullets of different calibers things get interesting and harder to predict.

What jmr40 is getting at is Sectional Density, which has shown a healthy correlation with penetration.

Here is some good reading, which does some of the caliber comparison jmr40 refers to:
https://www.chuckhawks.com/sd_beginners.htm
https://www.chuckhawks.com/sd.htm

But a high sectional density bullet with velocity=0 penetrates nothing. Velocity must be imparted on the bullet to make things happen.

So, the three factors to keep an eye on for terminal performace are:
Mass
Frontal Area
Velocity

Velocity is not to be overly weighted by squaring it as is done in the KE=0.5*M*V**2 formula.

=================

I think the take-away for handgun users is that (for the same cartridge or bullet diameter) increasing the mass of the bullet is a more reliable way to increase penetration than is increasing velocity of the bullet. This is important because without penetration to the target's vitals, nothing else in the realm of terminal performance matters.

Also important are bullet shape and materials, but your question seems focused on P vs KE as a factor in terminal performance.

pete2 · November 29, 2018, 10:49 AM

The bigger and heavier it is, the faster it goes, the harder it hits. No rocket science here.

idek · December 6, 2018, 11:45 PM

A few years ago, the Hornady website had something on their website called their H.I.T.S. calculator. I don't remember what this acronym stood for, but you'd enter a bullet's mass, velocity, and diameter, and it would spit out a number that you would then compare against a reference chart to determine what game animals that projectile was or was not suitable for.

Like most formulas, it didn't take into account the bullet materials, shape, or construction. But what it was basically trying to predict was penetration potential. And a little tinkering with the HITS results showed that it was really just taking momentum times sectional density (then times some other constant to yield nicer numbers).

So, at least according to Horndady, momentum is half the story when it comes to penetration. Sectional density is the other half.

pblanc · December 7, 2018, 08:51 AM

I agree entirely with jfruser. There are many factors that come into play so far as penetration is concerned. If we consider only non-expanding FMJ ammunition these include mass, velocity, sectional density, form-factor, and meplat.

Velocity and projectile mass are the primary determinate factors in both kinetic energy and momentum, but kinetic energy gives vastly greater weight to the velocity factor by squaring it whereas momentum is the simple product of mass and velocity. Obviously the two are closely related because as momentum goes up, so does energy, but energy increases exponentially compared to momentum because of the second power of velocity.

While there is no one simple metric that will determine terminal ballistic performance of a handgun projectile, I think that momentum does a better job of doing so than kinetic energy. Momentum is a primary determinate of what will happen to a projectile as it encounters media of different densities. A projectile with greater momentum will be more likely to penetrate denser media and remain on its original path without being deflected than one with lesser momentum, even if the second projectile has greater kinetic energy.

This is a factor not demonstrated in ballistic gelatin testing since ballistic gel is a medium of consistent density.

November 28, 2018, 02:55 AM	#1
simonrichter Senior Member Join Date: December 3, 2011 Location: Austria Posts: 758	Is there any correlation between momentum and penetration / terminal ballistics? I was just wandering how bullet momentum (velocity x weight, thus not weighing in velocity(2) like energy) influences terminal performance? __________________ "Get off of my lawn!" Walt Kowalski . ISSC PAR .223

November 28, 2018, 04:04 PM	#3
jmr40 Senior Member Join Date: June 15, 2008 Location: Georgia Posts: 10,809	No. Momentum is a good way to predict which rounds will more reliably knock over steel plates, bowling pins or other heavy objects. The best way to predict penetration, all things being equal, is bullet length in relation to weight. Longer bullets tend to be heavier in the same caliber, but when comparing bullets of different calibers things get interesting and harder to predict. Of course bullet construction and velocity are factors too. That is why I said "all things being equal" above. All bullets are designed to work best and expand well within a range of impact speeds. Too fast and they over expand and don't penetrate. Too slow and they may not expand. It is far from an exact science, but momentum is a poor way to judge bullets effectiveness. __________________ "If you're still doing things the same way you were doing them 10 years ago, you're doing it wrong" Winston Churchill

November 28, 2018, 05:16 AM	#2
collector rob Senior Member Join Date: November 2, 2005 Location: NW WASHINGTON Posts: 232	Good read from the Box o' Truth. https://www.theboxotruth.com/the-box...e-box-o-truth/

November 28, 2018, 05:41 PM	#4
themalicious0ne Senior Member Join Date: March 13, 2012 Location: Oconomowoc, WI Posts: 345	It depends on the medium and the amount of necessary penetration. For instance, if you were shooting at a bear with a handgun, a bullet with greater mass and momentum would probably be preferred for more penetration compared to one with less mass and momentum, even if they had the same KE. There are an unlimited amount of variables, a 22lr will penetrate Kevlar easier than a 45acp. Momentum will have an effect but it really just depends on the application and what you are comparing.

November 29, 2018, 10:49 AM	#6
pete2 Senior Member Join Date: May 15, 2012 Location: Texas Posts: 2,566	The bigger and heavier it is, the faster it goes, the harder it hits. No rocket science here.

December 6, 2018, 11:45 PM	#7
idek Senior Member Join Date: August 20, 2009 Posts: 903	A few years ago, the Hornady website had something on their website called their H.I.T.S. calculator. I don't remember what this acronym stood for, but you'd enter a bullet's mass, velocity, and diameter, and it would spit out a number that you would then compare against a reference chart to determine what game animals that projectile was or was not suitable for. Like most formulas, it didn't take into account the bullet materials, shape, or construction. But what it was basically trying to predict was penetration potential. And a little tinkering with the HITS results showed that it was really just taking momentum times sectional density (then times some other constant to yield nicer numbers). So, at least according to Horndady, momentum is half the story when it comes to penetration. Sectional density is the other half.

December 7, 2018, 08:51 AM	#8
pblanc Senior Member Join Date: March 23, 2008 Location: Indiana Posts: 697	I agree entirely with jfruser. There are many factors that come into play so far as penetration is concerned. If we consider only non-expanding FMJ ammunition these include mass, velocity, sectional density, form-factor, and meplat. Velocity and projectile mass are the primary determinate factors in both kinetic energy and momentum, but kinetic energy gives vastly greater weight to the velocity factor by squaring it whereas momentum is the simple product of mass and velocity. Obviously the two are closely related because as momentum goes up, so does energy, but energy increases exponentially compared to momentum because of the second power of velocity. While there is no one simple metric that will determine terminal ballistic performance of a handgun projectile, I think that momentum does a better job of doing so than kinetic energy. Momentum is a primary determinate of what will happen to a projectile as it encounters media of different densities. A projectile with greater momentum will be more likely to penetrate denser media and remain on its original path without being deflected than one with lesser momentum, even if the second projectile has greater kinetic energy. This is a factor not demonstrated in ballistic gelatin testing since ballistic gel is a medium of consistent density.