Let's talk physics!

[Rand McNally]

Ok, help me to understand because according to what I am reading I am way off:

http://greent.com/40Page/ammo/40/180gr.htm

I read this article the other day and it has me questioning the logic. In my mind, if you have a higher velocity, but with a lower weight bullet you would have a higher chance of over penetration. The goal is to have all the energy "dumped" inside your target for maximum effect. So if you have a faster traveling bullet that penetrates through the target, you have wasted the energy. Hence why the .45ACP travels relatively slow, but typically dumps all the energy upon impact (or within the target). Am I way off here? I guess to me slow and heavy seems more effective than fast and light. Of course you would also have to take into account the type of bullet (fmj vs jhp). But let's assume bullet types are all equal in this example.

I knew I should have paid more attention in school...

[bulletproof]

From my understanding of physics, bullets that can't penetrate are pretty worthless. Overall there is no such thing as over penetration when you're dealing with handgun calibers shot from short length barrels.

[yukonjasper]

I'm not a physicist and I don't think this guy is either, but he has some examples on his site that get into the engergy transfer vs wound channel etc.

http://www.rrmemphis.com/opinions.html

Take it for what its worth.

[Seismic Sam]

I'm in Barcelona, it's midnight, and I'm not going to write a book about this. Velocity does NOT correlate with penetration!! If you go too light and too fast, the bullet can blow up on impact and leave a nasty bu survivable 3" deep wound. Ther is also the differnce in the way you figure it, either in ft-lbs or Taylor Knock-Out factor. The way you are heading appears to be based on ft-lbs, which favors velocity over bullet weight and to some extent caliber, in that caliber isn't even considered in the ft-lbs calculation. Then there is the whole matter of bullet construction, which people like Elmer Keith wrote whole abooks about. Bottom line, it ain't that simple any way you cut it, and you have a lot more learning in front of you to fully understand this subject.

[Cuda66]

I can almost guarantee that sedate ol' 230gr .45 FMJ will outpenetrate a 4000fps+ 40gr V-Max from a .220 Swift...

[bulletproof]

I can almost guarantee that sedate ol' 230gr .45 FMJ will outpenetrate a 4000fps+ 40gr V-Max from a .220 Swift...

P.O. Ackley seems to disagrees with you. Comparing handgun calibers to rifle calibers is fairly silly.

[Cuda66]

I can almost guarantee that sedate ol' 230gr .45 FMJ will outpenetrate a 4000fps+ 40gr V-Max from a .220 Swift...

P.O. Ackley seems to disagrees with you. Comparing handgun calibers to rifle calibers is fairly silly.

I do wonder what type of bullet he was using; methinks a ballistic tip would come apart pretty darn quick.

Ah well.

[bulletproof]

I do wonder what type of bullet he was using; methinks a ballistic tip would come apart pretty darn quick.

Ah well.

You're right about the bullet being extremely important. You might not even get through a 2x4 board with frangible .45acp ammo. Certian .220 Swift bullets could easily disintegrate because of their high velocity and loose penetration effectiveness.

[Snowgun]

I'm in Barcelona, it's midnight, and I'm not going to write a book about this. Velocity does NOT correlate with penetration!! If you go too light and too fast, the bullet can blow up on impact and leave a nasty bu survivable 3" deep wound. Ther is also the differnce in the way you figure it, either in ft-lbs or Taylor Knock-Out factor. The way you are heading appears to be based on ft-lbs, which favors velocity over bullet weight and to some extent caliber, in that caliber isn't even considered in the ft-lbs calculation. Then there is the whole matter of bullet construction, which people like Elmer Keith wrote whole abooks about. Bottom line, it ain't that simple any way you cut it, and you have a lot more learning in front of you to fully understand this subject.

+1

This subject comes up over and over and over again, and it's because laymen have a difficult time grasping the subtle differences between momentum and energy. (I'm not being derogative mind you, since these things are not easy to fully understand, even if the equations seem simple.) Then, you add on top of it the effect of momentum or energy on viscoelastic media like tissue and bone, AND then you try to extrapolate from that the effect on a living system (stopping power, etc)......Voila! You have just jumped down the rabbit hole.

If you forget about the effects on tissue for a second, one can just look at the difference between momentum and energy (THEY ARE NOT THE SAME) to at least get a grasp of why there is confusion.

Momentum = Mass * Velocity. (you can use any measurement system you like, standard or metric)

Energy (Kinetic) = 1/2 * Mass * Velocity^2

We use these metrics because they are both "conserved" when talking about a system. This is a fancy way of saying they don't go away, they just get transferred from one object to another.

Lets talk about momentum first: The momentum of the bullet gets transferred to the steel plate, and imparts a velocity on the steel plate. Therefore it slows down the bullet, speeds up the steel plate, and knocks it down. If you add the two momentums of the bullet and the steel plate, they will be equal to the original momentum of the bullet.

Here is where Penetration comes in: The difference between momentum, is that this conservation principle is simple, meaning you are always talking about momentum (I will show what I mean below when talking about energy). Therefore, you are always talking about MASS times VELOCITY. Ok. Now lets talk about INERTIA. Inertia is the resistance an object has to having it's velocity changed. It is sort of represented in the mass of the object. If an object is moving, it will take some doing to decrease it's velocity. We typically change things through the application of FORCE

Force = Mass * acceleration

Ok, bear with me. So, if our bullet has a momentum = M * V when coming out of the barrel, in order for the bullet to STOP in the body, it will have to end up having a momentum of ZERO. In order to do that, since we can't change the mass, the VELOCITY will have to be changed to zero. We change the velocity of a particular mass with ACCELERATION (like slamming the pedal on your car to go from velocity 0 to velocity 60). Since from the above equation has F=M*A, this means that the tissue will have to impart a force on the bullet to stop it.

Assuming that tissue or ballistic gel will impart a standard force per inch of bullet traveled, changing the momentum to zero, THIS is why momentum generally equates to penetration depth.


Pfew! Ok, Not done yet, because I haven't talked about energy.

Right off the bat, let me point out the squared term on the velocity in the energy equation. This is the kicker for why people get confused. Even though we are putting in the same ingredients in momentum and energy, namely mass and velocity, we are treating them differently.

The awesome but tricky thing about energy.....is that although it is conserved, the tricky bastard can change forms on you. Just look at a nuclear reaction to energy process:

Mass (E=mc^2) - Heat - Chemical - Kinetic - Electrical - Heat - Light

Mass can be converted to heat, which changes states of water chemically to produce steam which changes the speed and therefore kinetic energy of turbines which spins magnets in solenoids to produce electricity which you use to heat a filament which gives off light. AWESOME! This is great for us sciency types who have to track all this **** as it changes forms, but it makes it a real bitch to intuitively understand where all that energy goes when something happens, like a bullet hitting tissue.

Pretty much, when a bullet hits tissue, the energy gets transferred to all sorts of places, doing everything from expanding the bullet if it is a hollow point, to creating heat, to displacing tissue, to creating shockwaves in the tissue and blood, down to even creating cavitation bubbles by changing the phase of the liquids in a body.

Not so easy to make a definitive statement on the effect of energy on terminal ballistics now is it? Except to be able to generally state that more energy is better all other things being equal. All things being equal is the kicker, since as Sam pointed out above, if you expend all your energy in three inches of fat, instead of penetrating into vital organs, the energy won't translate into what you want it to, which is "stopping power".

[minnesotatv]

From my understanding of physics, bullets that can't penetrate are pretty worthless. Overall there is no such thing as over penetration when you're dealing with handgun calibers shot from short length barrels.

BS.
test .357mag round nose lead or
.45acp FMJ out of short barrels.

[TTS]

Terminal ballistics has little to do with energy transfer.

Education is key:

We want to make you aware of the wealth of wound ballistics information available to you from sources other than newsstand gun magazines. Our objective is to provide you the knowledge tools you need to fully understand the qualities a bullet must have in order to be reliably effective in stopping a determined homicidal attacker.

Chances are, if you’re an average person, your primary (perhaps only) source of information about wound ballistics is what you've read in newsstand gun magazines. Problem is, most newsstand gun magazines are not a credible wound ballistics reference. Why?

Because a few questionable gun-writers (and editors) apparently recognize that magazine articles are the only source of information about wound ballistics for most people. It appears they’ve chosen to prey on a general lack of knowledge about wound ballistics to misinform and invent controversy. Controversy sparks reader interest and promotes sales. Most anyone familiar with the popular media recognizes this.

These discredited authors have been so successful in influencing the popular gun press (including honest editors and authors who don’t know any better) that most information published in newsstand gun magazines about wound ballistics is tainted.

The basics of terminal performance, wounding effects and wounding effectiveness are pretty easy for ordinary people to understand, and this creates a conflict of interest for some gun-writers because there really isn't much to write about.

Instead of sticking to simple facts these particular authors would rather delude you with paragraph after paragraph of mystical concepts such as "energy transfer," "neural shock," "Fuller Index," "one-shot stopping power," "Strasbourg Tests," and "street results." Although this stuff makes for interesting and entertaining reading, it's really nothing more than a bunch of sophisticated junk-science they've invented to ensure they have plenty to write about.

These pseudo-expert 'master psychics' of wound ballistics want you to believe only they (and they alone) possess the clairvoyance to properly interpret and evaluate the factors that make a particular bullet more effective than others. They tell an alluring tale, but these discredited few are actually snake-oil salesmen who've been quite successful in creating a market to peddle their brand of proprietary nonsense.

Having failed to influence law enforcement to any great degree, these gun-writers invented a new controversy: "civilians need personal defense ammo that penetrates the human body less deeply than law enforcement ammunition". Unfortunately, this kind of 'expert advice' can get you or a loved one killed if the shooting situation you face doesn't conveniently fit their stereotypical 'civilian self-defense shooting scenario.'

Wound ballistics is a specialty field that doesn’t receive much exposure outside the few professional disciplines that have a need for valid, scientifically verifiable information about ballistic injury. As a result, the average person isn’t aware this information exists or that it can be easily obtained. Sadly, this situation has allowed junk-science to flourish virtually unchallenged in newsstand gun magazines.

We’ve reprinted a few wound ballistics articles and put together a Suggested Reading list of publications from various sources, which, if you're interested, should help you learn more about the science of wound ballistics. Hopefully, the knowledge you acquire in reading these documents will keep you from being victimized by those unscrupulous few who seek to exploit your ignorance for profit.

Our goal is to instill a healthy attitude of skepticism in you so you're not as willing to believe everything you read. Hopefully, you'll learn enough here such that you'll be able to evaluate the qualifications of so-called ballistics experts.

More here:
http://www.firearmstactical.com/wound.htm

[bulletproof]

From my understanding of physics, bullets that can't penetrate are pretty worthless. Overall there is no such thing as over penetration when you're dealing with handgun calibers shot from short length barrels.

BS.
test .357mag round nose lead or
.45acp FMJ out of short barrels.

If you have a point feel free to make it since I'm not a mind reader. Are you suggesting that .357mag over-penetrates or something?

[jdege]

Simple truth is that at handgun velocities, wound channel is all that matters.

If the round is traveling faster than the speed of sound in water (>4800fps), there are a lot of hydrostatic effects, but at handgun velocities, wound channel is all that matters.

So for handguns, it's penetration and placement.

[Seismic Sam]

Thank you for writing the book, Snowgun - there was no way I was going to write all that after midnight, particularly when it was to answer a question that looked simple but was anything BUT simple.