Even a cursory scouring of gun forums, or listening to discussions at shooting ranges, will frequently uncover a discussion about “overpenetration” and the terrible dangers it represents.  Which is entirely understandable, as those of us interested in armed self defense are repeatedly lectured that “You are legally responsible for every projectile that leaves your weapon” and — if a bullet overpenetrates your attacker and strikes someone behind them, you are facing some substantial legal, financial, and emotional consequences.

Furthermore, fear of overpenetration is firmly ingrained by reading The Four Laws Of Gun Safety, where it’s stated: “Always be sure of your target, and what is behind it!”

With all that said, I’m going to raise a few eyebrows by just plain flat-out saying it: the paranoia about “overpenetration” is grossly overblown.  It’s not what you should be worrying about — or, well, it’s something you should be aware of, but it’s definitely not the most important thing and it’s not something to expend a tremendous amount of energy being concerned about.

Why Is Overpenetration (usually) Overblown?

There are a few reasons why I say this, but let me start with reason #1: you should be much more concerned with shots that miss the target entirely, than shots that penetrate through your attacker and keep going!  Missed shots are much, much more problematic than overpenetrating shots are.  There are lots of reasons for this, but I’m going to focus on two:

1.) You’re probably going to miss more than you hit.  Now, I’m not indicting you, or your marksmanship, or telling you you need more range time (although hey, we all need more range time).  I’m just acknowledging a simple, obvious fact — it’s really, really hard to hit a moving target when you’re terrified and fearing for your life and you’ve got more adrenaline coursing through your veins than you’ve ever experienced before and your body is overwhelming you with the “Fight Or Flight” instincts.  How hard is it?  Consider the statistics from the NYPD for officer-involved shootings — they’ve been keeping track of these stats for decades, and a brief study of them will reveal that for every six shots officers fired, they missed five of them.  Not “hit somewhere other than the desired point of aim”, not “hit in the shoulder” or “hit in the leg” or whatever, but — missed completely.  Five out of six shots fired by NYPD officers, on average, over the last several decades, missed the target completely.  Now, I know that some of you are thinking “well, that’s just because the NYPD has lousy training and officer certification, I KNOW I’m much better than they are!”  I’ve heard that argument advanced many times.  So I’d like to point out — the NYPD isn’t the only organization keeping statistics.  I’ve seen reports of more than a few, and in no case have I seen reports of the officers hitting more times than they missed.  Sure, the NYPD was the lowest ranked, but some other examples reported are Miami (between 15% and 30% from 1988-1994) and Portland at 43% (1984-1992); the highest I’ve seen is Baltimore reporting a 49% hit ratio.  Keep in mind, these are trained police officers.  Does that mean their training is superior to yours? Maybe, maybe not — how much do you train?  If you’re absolutely fervent about taking classes and training in true defensive scenarios, then maybe your training is on par or even better than the NYPD, but I’d dare say that that would be the case in only a minority, if not even a small or even tiny minority, of self-defense shooters.  For most of us, we go to the range once in a while, and we shoot paper targets.  That’s not training, that’s just rote marksmanship, and it has little (or nothing) to do with surviving a defensive encounter against a determined, fast-moving, armed attacker!

Secondly, I’d like to point out that police officers (yes, even those in the NYPD) are human beings who love their lives every bit as much as you love yours.  None of them wants to die.  I think it’s not likely that they’re blatantly ignoring training; whether the department offers top-line training or not, I think it’s likely that officers (who know very well that they’re far more likely to be shot at than the average citizen) even supplement their training.  And, given all this, they still only hit one time out of six.

What does that tell you?  It tells me that hitting a target, in that scenario, is really, really hard.  And you shouldn’t be surprised if you miss.  You should do your very best to hit, you should try your very hardest to hit, but — it ain’t easy.

Does this mean you shouldn’t even try?  Should you be so paralyzed by fear of missing, or fear of overpenetration, that you just put the gun away?  Again, let’s go back to why you’re carrying the gun in the first place… it’s likely (or should be) that you’re carrying it to protect you, or a loved one, from death or great bodily harm.  So if it’s a case of “don’t shoot and be killed” or “shoot and maybe you’ll have some consequences, maybe you won’t” then the old adage may apply here: “Better to be judged by 12, than carried by six.”

Now, on to reason two to not sweat overpenetration nearly as much as we seem to:

2.) Bullets get slowed down as they pass through someone.  A lot.  Let’s take the example of a .380 hollowpoint impacting an attacker at 1000 feet per second.  That bullet is capable of penetrating 13″ of ballistic gel.  Let’s say that it hits and passes completely through a thin attacker, and keeps going.  Assuming the bullet passed through, say, 9″ of soft tissue, how much of a threat will it still be? Using the formulas in Quantitative Ammunition Selection, we can find out — and doing the math, that bullet will still be traveling at 290 feet per second when it exits.  So yes, it’s capable of still doing some damage, certainly, but nowhere near as much as a missed shot would be!  Remember, the missed shot still has 100% of its velocity, so it’s still travelling at 1,000 feet per second, and it’ll hit something (a car, a wall, or maybe a bystander) and it will still be highly deadly.  The overpenetrating shot will still hit something too, but it’s at greatly reduced power.  It is much less likely to be deadly to a bystander than the missed shot would be.

Let’s take another example, the 230-grain .45 ACP JHP that travels at 850 feet per second — how much of an overpenetration threat would it be, after passing through 9″ of soft tissue of your attacker? Perhaps quite a bit less.  According to the QAS formula, that bullet would exit a 9″ torso traveling about 203 feet per second.  Now, that’s still capable of creating damage, but it’s certainly a much minimized threat as compared to a missed shot!

How much damage will these overpenetrating shots do to a person standing behind the target?  While there’s no way to predict exactly what will happen in any given scenario, we can look at probabilities and determine — they probably won’t do much damage.  How can I say this?  Thanks to ballistics experts and mathematicians who have modeled these parameters, we know that there’s a pretty good chance that these example overpenetrating bullets wouldn’t even break the skin of someone they pass-thru and hit.  Henry Hudgins of the US Army’s RDECOM Aeroballistics Division developed a formula for determining the velocity necessary for an expanded hollowpoint to break skin (with or without any chosen layer of clothing).  And according to Hudgin’s model, the .380 JHP I mentioned (exiting a 9″ torso and traveling at 290 feet per second) would probably sting when it hit someone else, but it’d be going slower than the 301.2 feet per second necessary to penetrate through 4 ounces of light clothing and then break skin.  And the .45 ACP example I gave, which exits a 9″ torso traveling 203 fps, wouldn’t even come close to the 295.6 feet per second necessary to punch through that 4oz clothing and then break skin.  So yes, that person may be bruised, but it’s probably unlikely that they’d sustain substantial or life-threatening injuries due to being hit by these example overpenetrating bullets.

Note, I’m not saying to ignore the concept of overpenetration.  I’ve embarked on an extensive quest to find the best .380 ammunition because I really don’t like the idea of using full-metal-jacket bullets that will easily penetrate 22″ of ballistic gel, because it seems like they’re guaranteed over-penetrators.  I certainly don’t want to accept the guarantee of overpenetration, when I don’t have to!  Hollowpoints are designed to expand so large that they minimize or largely eliminate the prospect of overpenetrating; most modern hollowpoints are designed to deliver about 12-13″ of penetration maximum.  But here’s the far bigger danger, to you: worrying so much about overpenetration, that you select ammo that actually under-penetrates.  That’s the real danger in this whole scenario.  Understand that an overpenetrating bullet will still stop an attacker; it just will also represent a threat to others (or property) by overpenetrating.  But an underpenetrating bullet is much more likely to fail to stop the attacker — and that means that the attack will continue.  Underpenetrating ammo was the whole reason for the debacle of the Miami FBI shootout, and the reason the wound ballistic conferences were called in the first place.  Underpenetration gets self-defense shooters killed.  Overpenetration may present some risk of collateral damage, but underpenetration presents the very real risk that you may not survive the encounter.

Overpenetration is bad, but underpenetration is much worse, and missing is far far worse.  Try to choose suitable ammo, and if you ever have to use it, try to be as accurate as possible, and you should be able to minimize your worries about overpenetration.

So what’s the general upshot?

Shoot only when you absolutely have to.  And be absolutely sure of your target, and do your very very best to hit them.  Be worried about missed shots, as those are far worse than overpenetrating shots.  And if a bullet overpenetrates, that’s disappointing, but the alternative (either not shooting, or using underpenetrating ammo) are both likely to get you killed.  A solid torso shot with a modern hollowpoint should minimize the risks of overpenetration.

Overpenetration can happen, but there are far worse things to be concerned about.  Don’t let fear of overpenetration unnecessarily cloud your judgement.  Choose reliable, effective ammo, and then train train train train with it, and pray you never have to use it.

How’s that for an attention-grabbing title?  Yeah, I know, sounds like no need for sleeping pills, it sounds like this article will put you right out, right?

Well, hopefully not so.  Hopefully this can shed some light on a new factor I’m introducing to my YouTube channel’s ammo tests: The MacPherson Wound Trauma Incapacitation (WTI) Factor.

I discussed the WTI factor in a previous blog article, http://shootingthebull.net/blog/how-effective-is-a-hit-from-a-judge/.  But I wanted to address it more head-on and more specifically, here in this article, so that when people see the end of my ammo tests and see a “MacPherson WTI Factor” quoted, they’ll know what it means.

What Is The WTI Factor?

In the simplest possible terms, the MacPherson WTI factor is an attempt by Duncan MacPherson, author of one of the seminal works on wound ballistics (“Bullet Penetration“), to quantify just how effective a bullet would be in stopping an attacker.  Now, there have been many attempts at doing this before; an example would be the TKO (“Taylor Knock Out Factor”).  The problem with prior models of bullet effectiveness is that they didn’t actually take into account what makes a bullet effective!  Instead they relied on (seemingly arbitrarily) assigning factors to caliber, diameter, speed, weight… all the right things, yes, but without knowing and modeling how they work together, and without knowing what actions of a bullet actually STOP an attacker, how can you rank them?

Voluntary Incapacitation

Let’s go through the reasons why an attacker would stop attacking.  There are many, but they basically break down to two categories: voluntary, and involuntary.  Voluntary factors include:

1. They see that you have a gun, and they decide to call it quits right then and there.  If not, then:
2. They see a gun pointed at them.  That can be a real attention-getter, staring down the barrel of a loaded gun.  It might be enough for them to decide that they’d be better off somewhere else, and fast.  If not, then maybe when:
3. They hear a gunshot, or see the muzzle blast.  Now, they may or may not have gotten hit, but just hearing the shot or seeing flames erupt from the front of a gun can be enough, in some cases, to get an attacker to drop what they’re doing right away.  If not, then perhaps:
4. They get shot.  This one starts to cross the line between voluntary and involuntary, but let’s stay strictly voluntary here — let’s say they get shot, with a flesh wound.  Nothing serious.  Maybe they got grazed.  Maybe they got shot in the leg.  Doesn’t really matter, all I’m after here is: it’s not life-threatening, but maybe it’s bleeding.  That right there will stop many attackers; many people will choose to stop their attack when they feel the panic of “I’ve been shot — I need to get to the hospital immediately or I’m gonna die!”

Okay, that basically covers the voluntary reasons someone might choose to stop an attack, in progressive order.  But what if they won’t?  What if they simply will not stop attacking, even after being shot?  Maybe they’re high, or so enraged, that they just don’t care or don’t even notice that they’ve been shot at all.  What then?  Well, at that point you will be relying on your defensive gun to FORCE them to stop attacking.  And that’s where you need to know how effective your bullets will be in causing wound trauma, and what level of wound trauma you’d need to be able to inflict in order to force even a determined attacker to stop.

Sometimes, Any Bullet Will Do

A side diversion here — sometimes, really, any bullet from any gun will do equally as well as any other bullet from pretty much any other gun.  Look through the list of “voluntary” reasons: in those scenarios, it very likely wouldn’t matter what bullet or what caliber you had on hand; if someone’s going to be stopped by hearing a gun fire, it’s not very probable that they’ll be thinking “oh, wait, that was only a .380, never mind, I’ll keep attacking.”  Instead, it’s pretty much the case that if someone sees a gun pointed at them, they’re not likely going to process the barrel size as part of their decision-making process.  Even the process of getting shot — obviously a big bullet would cause more wound trauma than a small bullet, but if we’re discussing the psychological reasons of when attackers stop attacking, then when it comes to a flesh wound, it probably wouldn’t make that much difference to an attacker.  Seeing blood pouring out of their bodies will be what forces their decision; they’re not likely to go measuring the hole in them to see what size of bullet they got hit by.

So this is good news, for those who advocate smaller pistols and smaller bullets — yes, there are many cases where they will be equally effective in deterring an attacker.  But (and, as Pee Wee Herman said, “everybody’s got a big but”… what about when you need to force them to stop?  What if you need to invoke an involuntary incapacitation?

Involuntary Incapacitation Factors

Sometimes the bad guy isn’t going to cooperate.  Sometimes they won’t go away.  Sometimes, you may need to use deadly force to bring the attack to a halt RIGHT NOW.  Sometimes you need to take away an attacker’s capacity to attack you — you need to take away their ability to attack you.  This is what we’ve been referring to as “incapacitation” — when the attacker’s ability to attack is taken away from them.  This can be through many different ways, including rendering them unconscious, or even dead or paralyzed.  Regardless of the method of forcing them to stop, this section is about the hard business of making them stop immediately.

There are two basic ways to bring about involuntary incapacitation — either through an attack on the vital structures of the body, or through overall collective damage to the body that the body just shuts down.

Attacking the vital structures is called making an “incapacitating hit”.  Damaging the vital structures (such as the brain stem, spinal column, or destroying something in the circulatory system that causes a big drop in blood pressure) will cause an attacker to stop immediately (in the case of a brain stem or spinal column injury) or will cause them to stop very soon (in the case of hitting an artery or the heart).  Those types of hits will interrupt the flow of blood and therefore will soon deprive the brain of oxygen, although this is not immediate; even in a case of completely destroying the heart, the brain may have enough oxygen to continue attacking for up to about 10 seconds.

Scoring an incapacitating hit on a determined attacker is no easy task.  Bullets are small, and the vital areas on a human body are also quite small; the spinal column is maybe 2″ in diameter.  In order to hit these structures you’ll need immaculate shot placement (more on that later)  Here, again, the caliber doesn’t really matter much — a .22LR hit to the brain stem will stop an attacker immediately, just like a .45 ACP or a 10mm hit to the brain stem.  It’s true that the bigger bullet will have a higher likelihood of hitting something than a smaller bullet would (meaning, the larger the bullet, the more chance it would have to turn a “near miss” into a “partial hit”) but, assuming your shot placement is perfect, then any bullet (that penetrates deeply enough) can get the job done.

The Myth Of Shot Placement

So now we get to the controversial part.  Scoring an incapacitating hit on a determined attacker requires immaculate shot placement.  And just about the only way to get that is dumb luck.

Luck?!?!  Yes, I said it.  Luck.  Because if you manage to place that bullet exactly where you wanted to, in the heat of an absolute life-or-death situation where you are facing imminent death (or great bodily harm, as the law allows) and your attacker is moving rapidly — well, good luck with your shot placement.

It’s often said “Shot Placement Is King.”  Yes, it is — that is absolutely true.  The problem is, the odds of you being able to control your shot placement to where you want it, are very low.  Think about what’s going on — you’re not facing a paper target.  You have a living, breathing human being, who isn’t standing placidly, they’re trying to kill you.  You’re going to have the mother of all adrenaline dumps going on.  You’re going to be gripped in the most severe case of “Flight Or Fight” that you will ever experience.  Your fine motor skills are going to go by the wayside.  You’re going to have tunnel vision.  And you’re going to have barely a second or two to draw, aim, and fire.  Oh, and your attacker is bearing down on you, moving as fast as he can — and moving targets are always much harder to hit.

Still feeling absolutely confident about your shot placement?  Still think that you’re going to hit that 2″ wide spinal column?  I wouldn’t be so sure about that.  I wouldn’t want to rely on my ability to bring about a “one shot stop” in such a scenario!  And I certainly wouldn’t want to count on my ammo because some guy wrote in some column that “this is a great round, it dumps a lot of kinetic energy into the target” or whatever.

Accordingly, MacPherson wrote a 300+ page book to describe exactly what bullets do, how they behave, what they do to living tissue, what effects will stop someone immediately, and so on.  The net result is a formula that MacPherson predicts will have the potential for stopping an attacker, through general tissue damage — i.e., not relying on an incapacitating hit to the central nervous system.  He bases his formula on the general idea of overall tissue damage causing the body to shut down, as verified in an old Thompson-LaGarde test where steers were shot in non-vital areas with various calibers until they dropped.  It can be presumed that the steers weren’t influenced by any of the psychological factors, because the steers wouldn’t know what a gun was, wouldn’t know that having been shot meant they needed to get to the hospital, etc.  And, by avoiding the central nervous system or circulatory system, they showed that general damage to the body in sufficient quantity would be enough to cause the steer to drop.

So How Do I Use This?

In MacPherson’s work, he produced a formula that takes into account the penetration depth, the amount of tissue destroyed, and the type of bullet (a hollowpoint, a round-nose FMJ, a buckshot ball, etc) and comes up with a mathematical number that represents the amount of vital tissue that will be destroyed by that particular bullet.  MacPherson says that about 40 grams of tissue would need to be destroyed in order for the body to undergo such shock that it might shut down (again, there’s no guarantee, but this is about as good as he could predict).  40 grams of tissue is about as much as a hot dog, and I think you could imagine how substantial an injury would be if someone carved a complete hot dog out of your body!

In my ammo tests I’ll be reporting the MacPherson WTI (Wound Trauma Incapacitation) Factor, which will let you get a general idea of how one bullet compares to another when considering how much tissue it damages.  The MacPherson WTI is biased away from shallow-penetrating flesh wounds (for example, a really big-diameter bullet that only penetrates a few inches, would rate a zero on his scale; his scale requires bullets to reach deep enough that they’re not just damaging muscle, but are reaching the deepest internal sections of the body).  It also penalizes overpenetration; if a bullet just zips right through the attacker and wastes its energy by exiting the attacker, then he only credits the bullet with the damage it would have done within the attacker.  Obviously, an overpenetrating bullet won’t be as effective as one that puts all its available energy to work damaging as much tissue as possible.

It is in this arena, the involuntary incapacitation through tissue damage arena, where caliber becomes much more important.  For voluntary cessation of activities, any caliber will do.  And for critical hits on the central nervous system or major blood vessels, a hit by any caliber will be effective.  But when it comes to stopping an attacker without those critical hits, then the bigger, deeper-penetrating bullet that damages the most tissue is the one that will bring about involuntary incapacitation sooner.

MacPherson’s level of damage necessary for incapacitation is about 40 grams.  In the .380 ACP hollowpoints I’ve been testing, most are delivering MacPherson WTI factors of around 18 to 23.  What this means should be pretty obvious — don’t go betting your life on a “one shot stop” with a .380!  It’s going to take at least two or three good solid hits before you’ve damaged enough tissue in the attacker that they may be forced into an involuntary shutdown.  CAN you stop an attacker with one shot of a .380? Of course, if you have perfect shot placement and you hit a vital structure or the central nervous system.  But considering that the odds are quite against that, it would be wise to not rely on a “one shot stop”.  Instead you should count on the idea that you’re going to have to “shoot until the threat stops” — and that will likely mean at least two or three shots.  Now, I’m not going to guarantee to you that someone will stop after getting hit in the torso with two or three .380 ACP hollowpoints!  Obviously every shooting scenario is different, and the performance of bullets can vary from shot to shot, and it would also depend on whether the bullets hit something important (a vital organ) or just passed through muscle.  But in general, if you do your part and place the shots at least in the main torso, destroying 40 grams of tissue is perhaps going to bring about incapacitation even if you don’t get that rare CNS or artery shot.

Bigger bullets and bigger calibers make this easier, obviously.  Many .45 ACP hollowpoints will deliver a MacPherson WTI of about 55, meaning that it’s possible (not saying probable, but possible) that one solid shot to the body might bring about incapacitation.  Even then, I would still recommend following the advice of your firearms instructor when she says “shoot until the threat stops”.  But the larger bullet will give you a higher likelihood of hitting one of the critical structures in the body, and it will also destroy more tissue which may lead to faster incapacitation even in cases where it doesn’t hit one of those critical structures.

Reporting the MacPherson WTI will let you gain a better idea of how effective the bullets I test may prove to be if you ever need to use them.

In Summary

When selecting your defensive ammunition, here are the factors as I see them:

1. Any bullet, placed perfectly and penetrating deeply and hitting the central nervous system (CNS) or a major artery or the heart, will stop an attacker just as well as any other bullet would.  In this case, caliber does not matter.
2. Under the stresses of actual combat and the massive adrenaline dump that goes on, and the nature of a moving target who is attacking you and everything else that’s happening… there is practically no way that the average shooter is going to place that bullet perfectly.  It just will not (likely) happen.
3. Knowing the results of the Thompson/LaGarde tests, and knowing that there were no psychological factors involved that caused the steers to drop, it seems obvious that with enough tissue destruction, even hits in nonvital areas CAN cause incapacitation.  They won’t always do so, but they could.
4. Given the uncomfortable but clearly obvious truth of #2 above, it seems prudent to have a backup plan — being, have on hand the capability to administer enough non-critical wound trauma that you can still incapacitate the attacker even without that miracle CNS shot.

Place your shots as well as you can.  Practice as much as you can.  Practice speed and accuracy, practice moving while shooting, practice practice practice.  But when it comes to betting your life on being able to hit a tiny spinal column in a moving attacker while you’re moving and dodging and your fine motor skills are gone due to a huge influx of adrenaline… well, let’s just say that I wouldn’t want to rely solely on my ability to make that miracle shot.  Knowing how bullets work, knowing how they damage tissue, and knowing how much tissue damage is necessary before involuntary incapacitation might come into play, prepares you to be better equipped to successfully defend yourself if the time ever comes.

Interesting thing about “conventional wisdom” or “things everybody knows” — they’re frequently wrong.  You know, simple examples like “the earth is flat” or “the sun revolves around the earth”… these are plainly obvious things to anyone with eyes, right?  Look around you, and you’ll see that the earth is flat — except for the tiny complication that, in fact, it isn’t.  And the prevailing notion that the sun revolved around the earth was not only widely accepted “fact”, it was literally heresy against the Church to say otherwise… even though, in actuality, it was wrong.

It doesn’t really matter how widespread a belief is, does it, if it turns out to be wrong?

Sometimes I think people hide behind false beliefs because “there’s strength in numbers”.  If lots of people believe the same thing, then nobody could blame YOU if you believed it too, right?  You know, the old “everybody’s doing it” argument?

But — wouldn’t you rather be “right” than “popular”?  Hmmm, even as I type that I can acknowledge that there’s probably a lot of people who would disagree… oh well, to each their own, I guess… I know I’d certainly rather believe what is true, regardless of how many other people agree.

Where am I headed with this?  Just that I’m challenging one of the most dearly cherished beliefs among shooters: Muzzle Energy, Muzzle Velocity, and specifically the idea that More Kinetic Energy Is Better.

Shriek!  Sacrilege! 

Of COURSE more is better!  How could anyone suggest otherwise?  Heretic!

Yeah, I know… heretic.  Kind of like that whole sun-revolves-around-the-earth thing, right?  Here’s the thing — to me, it doesn’t matter what we WANT to believe, all that matters to me is what is TRUE.  I’ll gladly change my beliefs to line up with the truth, any time.  Never been one to go along with the crowd anyway.

So let’s talk about “Muzzle Energy”.  This is one of the most common ways, and most obvious ways, that shooters judge the effectiveness of ammo.  The more “energy” a round has, the better, right? Who could argue with that?  I mean, the common conception is that the faster the round, the better.  Seriously, if you had a choice between two rounds that use the identical same bullet, and one is rated at 1000 feet per second, and the other is rated at 900 feet per second, and they’re the same price, wouldn’t you have to be a raging idiot to buy the 900fps version?

What if I told you the 900fps version actually penetrates deeper and performs better than the 1000fps version?

For some of you, that feeling you’re experiencing right now is called “cognitive dissonance” — where your brain hurts, trying to reconcile two conflicting “truths” — you know (or at least want to believe) that I’m right, or else why would you be reading this article? But simultaneously, you also know that “more = better” because … hey, come on, it’s faster, therefore it MUST be better, we all know that…

Testing Trumps Theory, Every Time

So here’s where testing comes into play, and where I can demonstrate what I’m talking about and how it’s different.  Let’s take the example of Speer Gold Dots in .380 ACP.  I got pretty solid results with these out of the 2.84″ barrel Taurus TCP, averaging about 920 feet per second and 11.71″ of penetration through ClearBallistics gel.  From a Bersa Thunder 3.5″ barrel, I got substantially higher velocities, averaging 980 feet per second.  That’s great, right?  That’s “better”, right?

So here’s the head-smacking part — why did I get an average of only 9.5″ of penetration from the 980 fps Bersa Thunder, whereas the exact same bullets delivered 23% more penetration from the shorter-barrel, slower TCP?

It’s Not What You’ve Got, It’s How You Use It

Unquestionably, the Bersa Thunder’s longer barrel resulted in more energy in the bullet than the TCP’s shorter barrel did.  By my calculations, the TCP delivered 169 foot/lbs of muzzle energy, whereas the Bersa delivered 192 ft/lbs!  That’s a pretty huge difference, yet the relative effectiveness of the bullets were exactly the opposite — the TCP bullets penetrated deeply enough to cause an incapacitating hit, nearly meeting the FBI’s specification for a minimum of 12″ of penetration, whereas the exact same bullet from the Bersa came up way short, not even reaching 10″.

Why?  Because the bullets from the Bersa, travelling at such a higher rate of speed, impacted the ballistic gel much faster and spent all that additional energy on EXPANSION, not on PENETRATION.  The bullets from the Bersa did indeed have a lot more energy, and they spent it on forcing the bullet to open up to a bigger diameter.  The bullets from the Bersa expanded to an average diameter of .515″, whereas the slower bullets from the TCP expanded to only .447″.  That’s a difference in overall diameter of about 15%, which doesn’t sound like a lot, but it made a much bigger difference in the penetration (about 23%).  The smaller bullet was able to slip deeper into the ballistic gel than the bigger bullet could, even though the bigger-expanded bullet had a lot more energy to it.  And, all other things being equal, the bullet that penetrates more is more likely to reach the vital structures of the body and cause an incapacitating hit, than the shallower bullet.

If More Isn’t Better, Then Why Is More Better?

So here’s where we bring it full circle.  The natural inclination is to want more, and it seems obvious that we should want more, but — it all depends in how you use it.  You CAN do more, with more.  Having more energy at your disposal gives you more options than you’d have with less energy.  But if it’s not used wisely, it won’t help, and that’s the key.  As a bullet designer, spending too much of your available energy on expansion can result in an excessively shallow-penetrating bullet (as I discovered in my tests of the Winchester PDX1, for example).  Spending too much of your energy on penetration can result in wasted energy (as in the case of full-metal jacket bullets, which usually penetrate way too deeply and frequently will overpenetrate and exit the body, thus wasting their energy).  The ideal situation is where the designer crafts a bullet that expends enough of its energy on getting adequate penetration (ideally 15″, a minimum of 12″, and a maximum of 18″) and then uses any leftover energy for expansion.  That would be the ideal tradeoff resulting in the most effective bullet design for self defense purposes.  And if there’s so much energy at your disposal that even after you’ve achieved adequate penetration and nice expansion that you still have energy to spare, you can make good use of that additional energy by making the bullet heavier; the more energy you have, the heavier the bullet you can push.  And in that context, having more energy can be a great thing — take the example of 9mm vs. .380 ACP.  It’s a great illustration because the bullets are in fact identical diameters; the .380 ACP is also known as the “9mm Kurtz” or “9mm Short” or, sometimes, by the 9x17mm nomenclature, whereas the 9mm is also known as the  “9mm Luger” and as a 9x19mm.  Same diameter, sometimes even the same bullet, but the 9mm Luger cartridge is capable of much higher power.  Whereas the .380 is a marginal cartridge in terms of power, the 9mm is much more powerful, and while the .380 requires very careful and meticulous controlling of expansion to achieve the desired penetration, the 9mm has so much energy that it can easily achieve both great expansion and great penetration, even with heavier bullets (the typical .380 hollowpoint is usually about 90 grains, whereas with the 9mm they are usually at least 115 grains and can be as heavy as 147 grains).

So more can be better, when it’s used appropriately.  Or more can ruin the balance and give you results opposite of what you intended!  Don’t get caught up in thinking that “more always = better”, especially when it’s applied to a term like Muzzle Energy.  More can actually get in the way of better performance, as demonstrated by my .380 Gold Dot tests, or my tests of HPR XTP, where the HPR rounds are specifically loaded to less muzzle energy than the Hornady Custom, and actually perform better than the Hornady Custom, even though Hornady Custom uses the exact same XTP bullet, just with more muzzle energy.

Okay, So How Do I Choose The Best For MY Gun?

So how do you know when the ammo makers get the balance right?  That’s not an easy question to answer, but the first thing to do is: IGNORE THEIR MARKETING. Ignore claims for muzzle energy and “energy transfer” and “energy dump” and “hydrostatic shock” and “stopping power”.  Marketing is marketing, it’s designed to appeal to emotions, which is exactly the opposite of what you should be basing your decisions on.  Only valid testing can reveal what will work best — and, only testing that is conducted from a barrel similar to that in your gun, will provide answers that are valid for you!  As given in the example above, Gold Dots from a TCP might be quite effective, and the exact same Gold Dots from a Bersa Thunder might be much less effective!

The ideal solution would be for you to test your ammo from your gun.  Knowing that not everyone will, or even can, conduct such testing, the next best thing is to look for tests and reviews that were competently done, by people who know what they’re doing, and that were conducted from guns with similar barrel lengths to yours.  For the .380, I’ve conducted extensive testing from a TCP, which has a 2.84″ barrel, and as such my results should be directly applicable to those with similar barrel lengths, such as the Ruger LCP (2.75″ barrel) or Beretta Pico (2.7″ barrel) or Sig 238 (2.7″ barrel), etc.  But my results would likely not be directly applicable for a Bersa Thunder (3.5″ barrel) or Walther PPK (3.35″ barrel).  Those barrels are long enough that they make a significant difference in velocity and muzzle energy, and those differences will mean that the bullet may very well behave differently in how it allocates that energy (in terms of the balance between penetration and expansion).

There is probably an ideal-performing round for your gun, whatever the barrel length.  But you can’t rely on “muzzle energy” or “muzzle velocity” comparisons to find that round.  Only proper testing will reveal what the best round is — and it may very well be the round with the least muzzle energy, or the slowest velocity.  As an informed member of the self defense community, we have to be okay with that.  It’s not about bragging rights, it’s about effective performance.  After all, I’m okay with my bullet moving slower, so long as it renders the attacker incapacitated.