WHAT ABOUT BONES?!?!?!

(sorry for shouting, but — I get that question a lot.)

If there’s one common, frequent question I get asked more than any other, it’s — what about bones? Why don’t you factor bones into your equations? Why don’t you put pork ribs in your gelatin tests?  Why doesn’t ANYONE test with bones?

I tried to address that subject in a prior blog post (here).  But seeing as the question just came up again, I decided to do a little more research on the subject to see if I could present the information in a different way, that may help make it a bit more understandable and approachable.

You Can’t Just Go Shoot Pork Ribs

First thing to face though, is: living tissue and dead tissue are not the same.  The dried-out bone that you give your dog to chew on, well, that bone seems like it’s as hard as a brick or made of stone.  The living bones in your body, however, are very different — when they’re alive, they’re hydrated, and they’re (comparatively) flexible.  Bones aren’t some big impenetrable wall of indestructibility, they’re — living tissue.  Harder than other tissue, yes, but still, living tissue.  They grow, they get longer, they break, they heal, they’re alive, and they’re very different from the dead hard cow skulls you encounter when wandering through a desert oasis…

… so, back to the question of bones.  Why don’t we use bones in gel? Because they’re absolutely unpredictable, they’re not consistent, they vary in size and composition quite a bit depending on the individual, their size, their weight, their level of osteoporosis, and they can vary significantly in their composition (such as whether it’s a thigh bone or a skull bone!)  And the penetration or deflection or bullet deformation that happens is absolutely and entirely dependent on the angle that the bullet hits the bone at, and at the angle that bone itself presents to the bullet (i.e., hitting the triangular peak of an arm bone or the rounded edge of a rib is going to affect the bullet very differently from smashing head-on (literally) into the front of the skull. Trying to account for the effects bone would have on a bullet’s performance is a nearly impossible task, due to the sheer overwhelming number of variables involved.

But Let’s Give It a Shot (hah!) Anyway…

However, attempting to solve Herculean tasks can be a little fun, so … I’ll try.  A bit.  With the understanding that nothing I say here will rule out the freak incidents where a bullet bounces off a skull or deflects off a rib or whatever.  We can’t predict those, we can’t rule those out, but we can say those aren’t typical or normal.

So — how much effect does human bone have, on slowing down or affecting a gunshot?  Not a whole lot.

(uh-oh, I’ve done it now…)

Okay, stick with me.  I know there’s a thousand anecdotes out there, and I know that there are people who know people who know someone who once got shot and their pinky stopped the .44 magnum bullet cold and we’ve all heard about the guy who got shot in the face by a .45 ACP that traveled under his scalp and ended up exiting out the back of his head without ever even penetrating his skull and all that, but — again — those are not the norm!  They’re atypical.  We can’t account for every possible variation or every imaginable circumstance.  All we can do is look at it generally, and examine tissue penetration based on observable science and the laws of physics and in light of the studies that have been done.

In general, we know that bullets go through bones.  There are innumerable headshots and chest shots that attest to this.  Sure, there are exceptions, but there are exceptions to just about every general observation — it would be foolish to ignore the mountain of evidence and focus solely on the exceptions, right?  If we did a study of a thousand suicides through headshots and (say, pulling a number out of a hat) 996 showed bone penetration, and four showed that the bullet bounced off, I think it’s only practical to determine that bullets as a rule do penetrate bone 99.6% of the time, right?  Those few cases where it bounced off would be relatively statistically meaningless in the general discussion of whether bullets can and/or do penetrate bones.  Note: I don’t KNOW those statistics, so if anyone wants to point a link to a verified study that shows the percentage of headshots that result in the bullet penetrating the skull, vs. the percentage of headshots where the bullet bounced off the skull, I’d be very interested to review that data and update this article to reflect it.

So let’s get to the central question: how much effort does it take for a bullet to go through a bone?

Is Human Bone A Bullet-Stopper?

Not really.  In a study in 1968 by Donald F. Huelke, J. H. Harger, and others, they undertook to find out what happens when steel sphere projectiles impact human femurs.  Which may be morbid, but it’s also interesting to see, in that very few tests have been conducted specifically and scientifically on human bones.  And the femur is the largest bone in the body (although I really would have preferred that they do their study on ribs or the skull, beggars can’t be choosers, and for purposes of our article here we gotta start somewhere so we’ll go with the femur study.)

They fired two projectile sizes, .25″ and .406″ (roughly about the size of a #4 buckshot ball or a .25 ACP bullet,  and a .40-cal S&W or a 0000 buckshot ball) at dozens and dozens of actual human femurs, and recorded the damage done to the femurs, as well as the impact speed and the exit speed of the projectiles.  In other words, they catalogued exactly what the impact with the bone cost the bullet.  Knowing that, we can hope to add to their findings by calculating just how much power the bullet would retain and how much more damage it can do, after having impacted the bone.

(Side note, it’s interesting to me that they determined that embalmed bone was a good substitute for actual living bone.  I have not verified that through other studies or sources, but will have to go on their word for now.  We know dried-out dead bone is a lousy substitute for living bone, but apparently the embalming process allowed the bone to retain similar properties to when it was living… at least, according to this study…)

So what did Huelke and Harger etc. find?

A .40-caliber ball at as slow as 252 feet per second was able to punch entirely through the bone, although it was only traveling at 40 feet per second after exiting the bone (and, thus wouldn’t have penetrated much further).  Considering that the average 9mm round is usually traveling 4x as fast and weighs a good 30% more than the sphere they tested, it’s a pretty safe bet that the 9mm is going to have no trouble going through bone.

So Now Let’s Bust Out The Calculator…

If we examine their data at typical handgun velocities for the size of the rounds, and run the data through the Schwartz Quantitative Ammunition Selection formula, we can determine penetration depths and remaining penetration capability and, effectively, figure out just how much penetration their spheres “lose” from having to first penetrate a bone.

As an example, let’s take a .406″ sphere such as they used.  They used a steel sphere, which would weigh a little over 69 grains.  A lead sphere would weigh more but, interestingly enough, in a follow-up study they determined that weight was irrelevant for the purposes of determining the damage done; they instead found that size and velocity were the determining factor, so … in interests of keeping this approachable, I’ll substitute in a 90-grain .380 ACP bullet and a .40-cal 000 buckshot ball for the .406″ sphere.  They’re not a direct comparison, but they’re relatively similar to the tested steel sphere, at least ballpark similar.  A 90-grain .380 ACP FMJ should travel at about 820 feet per second when fired from a 2.8″ micro-pistol, and a load of NobelSport 40-caliber buckshot is rated on the box for 820 fps velocity, so — the parallels are too convenient to ignore, so let’s use an 820fps velocity for the start of our comparison.  Using Huelke et al’s data from page 100 of their study, it shows numerous entry and exit velocities for the .406″ sphere.  Let’s examine the closest line, which is 814 feet per second, which gives us the most reasonably comparable approximation of our 90-grain round-nose .380 ACP FMJ and our .40-cal buck ball.

According to Huelke et al’s data, the sphere at 814 feet per second blasted through the bone with an exit velocity of 619 feet per second.  Using the Schwartz formula, I find that a 69.4-grain steel sphere at 814 feet per second would penetrate 13.04″ of soft tissue, but here’s the fun part — it would be slowed down to 619 feet per second after traveling only 2.44″ of flesh!  So what did the bone impact cost the bullet, in terms of penetrating power? Only 2.44″.  After passing through the bone, that steel sphere would still be able to penetrate 10.60″.

Put another, simpler way: the steel sphere started out at 814 feet per second, but after passing through a bone, it was down to 619 feet per second.  If we fired that steel sphere into muscle tissue instead of bone, it would slow down to 619 feet per second after only 2.44″ of tissue.

So the impact with the bone lopped off about 2,44″ of the bullet’s ability to penetrate flesh.

That ain’t that much.

Okay, let’s try now with the .380 ACP equivalent — 90 grain, .36″ in diameter, so about 10% smaller diameter than the steel sphere.  This isn’t going to be exact because, of course, the bullet size isn’t exactly the same, but I warned you at the beginning that we can’t be exact because of the millions of variables present in such an experiment, so … let’s roll with this as another variable, okay?  A .380 ACP 90-grain FMJ, which is close to the same weight and close to the same velocity as Huelke’s .406″ steel sphere, when traveling 814 fps will (according to QAS) penetrate 16.48″.  In order to bring the velocity down to Huelke’s observed 619 feet per second, how much flesh would the bullet have to cross?  Just 3.01″.  That’s it.  After smashing through the bone and dropping to 619 fps, the bullet would retain enough power to penetrate an additional 13.47″.

Seems like that bone isn’t an impenetrable wall after all, doesn’t it?

Now let’s try it with a more-similar projectile; we’ll use a spherical buckshot ball that measures .40″.  This should be exactly the same size and speed as what Huelke et all used, and although the weight is a little heavier for a lead sphere vs. a steel sphere (about 95 grains vs about 69.4 grains), remember that in their follow-up study they found that weight wasn’t a determining factor in the amount of damage done to the bone so, again… we’re gonna roll with it.  From a Raging Judge, I measured .40-caliber buckshot as penetrating an average of about 17.56″ (IIRC) into calibrated 10% organic ordnance gelatin.  According to QAS, those 96-grain lead .40-caliber buck balls, at 814 feet per second, should penetrate 17.49″.  Seems like an ideal comparison point to me…  especially because the ammo is rated on the box for 820 fps, so it seems like everything’s lining up.  So how much would the bone slow those buckshot balls down?  Again, using the exit velocity of 619 fps, QAS tells us that it would only take 3.25″ of flesh to equal the velocity drop that Huelke observed.  Now, sure, that’s a drop, but — is it that much?  With a round that would normally penetrate 17.49″, shaving off 3.25″ due to bone still leaves it able to penetrate 14.24″ of flesh, after it’s burst through the bone.  And that’s still plenty enough to reach the vital organs and disrupt them.

What About A Different-Size Bullet?

In their study, Huelke et al didn’t compare solely .406″ spheres, they also conducted tests from .25″ spheres.  We can run a comparison to see how they did simply and easily enough.  Let’s take as an example a .25 ACP FMJ bullet, the same diameter (but obviously not the same weight) as their lead spheres.  We’re looking mainly for a reasonable velocity here, so — according to SAAMI, a 35-grain .25 ACP bullet should travel at about 900 fps.  So for our calculations, we’ll use Huelke’s 900fps data.  According to them, at 904 fps, a .25″ steel sphere (which weighs 16.4) grains will blow through a femur and still be traveling 558 feet per second when it exits.  Well, using the Schwartz formula, it says a 16.4-grain steel sphere at 904 fps would normally travel 9.67″ through tissue, but it would drop to 558 fps after only 2.75″.  Again, this is quite consistent with what we’ve seen from the .406″ sphere, is that having to go through a bone only costs about 2.5-3″ of flesh penetration from a bullet’s total.

Now let’s take a 35-grain .25 ACP FMJ and put it at the same velocity.  Unhindered it would pass through 14.91″ of tissue, but if it hit first hit a bone and its velocity dropped to 558 fps after clearing that bone, its total penetration would be 4.24″ less.  This is the worst case we’ve seen for how a bone would impact the penetration, and even then — it’s not all that much.  From 14.91″ down to 10.67″ is a drop, certainly, but not the impenetrable brick wall that bone may appear to be.

Accounting For The Weight Discrepancy — or, AHAH! The Flaw In The Science!

I said at the beginning that it would be impossible to account for all the variables, but there’s one here that I do want to account for, and that’s the weight difference between steel and lead.  In the Huelke study they used steel spheres, not lead balls, and in bullets we typically don’t use steel, we use lead.  Trying to translate the impact of steel balls into the impact of lead balls will raise some mathematical questions, but I want to address it because it’s possible someone might think that my conclusions are erroneous because I tried to equate the exit velocity of the lead ball to the exit velocity of the steel ball.

It’s true that Huelke et al did a follow-up study to assert that diameter and velocity of the projectile were the determining factors in bone damage, and that mass was irrelevant.  I find such a conclusion challenging to accept on face value, because I know for a fact that mass is highly determinant in penetration.  As an example, a steel sphere of .406″ fired at 1000 fps will penetrate 14.95″, but a lead sphere of .406″ would weigh more and, when fired at that same velocity, would penetrate over 20.46″.  So I have a skeptical eye towards that part of the study, but I think it’s pretty easily resolvable.

To determine the effect of mass, they fired steel spheres, and identical-sized spheres of Heavimet, which is a tungsten carbide alloy that’s 2.18x heavier than steel.  That way they had identical diameter and identical velocity but more mass.  Their observed bone destruction was the same between both (which is why I was okay with the idea of using lead bullets as compared to their steel spheres) but — here’s the kicker — they didn’t measure overall penetration!  Once it got through the bone, that’s all they were concerned with; they weren’t measuring the ongoing penetration (which is what I, and I think most terminal ballistics aficionados, would be interested in knowing).  And, frustratingly, while they measured exit velocity with the steel spheres, they didn’t report exit velocity with the Heavimet spheres.  Instead, they only reported the amount of kinetic energy lost, and, further, they didn’t report it as a percentage of impact energy, they only reported it as an absolute number of ft/lbs. Grrr. So, I have to back-figure velocity and energy impact data to figure out what the exit velocity actually was.

Based on the Heavimet study, they say that an 1100 fps steel sphere lost 25.1 ft/lbs of energy by impacting the bone, and a Heavimet sphere lost 26.2 ft/lbs of energy impacting the bone.  Because those numbers are similar, they used that as an argument to say that the sphere imparted about the same amount of energy to the bone and cause a comparable amount of damage (which they verified by visual examination of the damage.)  BUT — what they’re not saying is that the exit velocity of the Heavimet sphere would be the same!  Because it wouldn’t.  The additional mass of the Heavimet means it has more kinetic energy, and that mass will help it retain its momentum better. Using their numbers, a Heavimet sphere of 2.18x the weight of steel, at the same velocity (1100fps) would contain 2.18x as much kinetic energy in the first place (96 ft/lbs, as opposed to 44 ft/lbs for the steel sphere).  So even though they lost the same AMOUNT of energy, proportionally the Heavimet sphere lost much less of its total energy — and, therefore, we can deduce that it retained higher velocity.

So — let’s go back to our original 814fps sphere and compare for exit velocities.  In the original experiment, the steel sphere went 814 fps and weighed 16.4 grains, for a total of 24.12 ft/lbs of energy.  And, they say it had an exit velocity of 558 fps, which would give it 11.33 ft/lbs of residual kinetic energy, for a total loss of 12.79 ft/lbs of energy.  But a Heavimet sphere weighs 35.76 grains, and at 814 fps it would possess 52.60 ft/lbs.  If it lost 17.2 ft/lbs of energy by passing through the bone (which is what their chart shows in table 1 for a Heavimet sphere at 800 fps), that would give it a residual kinetic energy of 35.4 ft/lbs.  Well, in order for a 35.76-grain sphere to have 35.4 ft/lbs of energy, it would have to be traveling at about 670 feet per second — much faster than the 558 fps that the steel sphere retained!

So what does this mean?

It means that the numbers I gave you above (2″ – 4″ of penetration lost due to bone) are probably grossly conservative, and the true penetration loss is even less.  For example, let’s calculate the 35-grain .25 ACP at 814 fps.  Previously, using the steel sphere’s exit velocity, we came up with a loss of 4.24″ of total penetration due to the bone.  But that was based on a steel sphere’s mass.  Since the HeaviMet bullet weighs basically the same as our .25 ACP bullet’s real mass (35 grains), we can perhaps extrapolate that the velocity loss of one .25″-diameter 35-grain projectile (the Heavimet sphere) will be quite comparable to the velocity loss you’d see with another .25″-diameter 35-grain projectile (the .25 ACP lead FMJ).  So, assuming that the exit velocity will be similar, let’ see how much penetration it takes to drop the velocity of the .25 ACP down to the Heavimet sphere’s exit velocity of 670 fps… according to QAS, an 814-fps 35-grain .25 ACP FMJ will drop to 670 fps after traveling through just 1.5″ of tissue.

One More Caveat

Okay, last monkey wrench to throw in is: this is for round-fronted objects (buckshot balls, steel spheres, or full-metal-jacket round-nose bullets).  This doesn’t take into account hollowpoints or bullet deformation that may happen due to impact with a bone.

(Like I said before, there are a MILLION different variables, and it’s going to be nigh unto impossible to account for them all!)

Conclusions? Are There Any We Can Reasonably Reach?

In general, based on our spitballing and on the scientific studies of Huelke et al, we can leap (however unjustified and tenuously) to the conclusion that hitting a bone will usually result in losing about 2″ to maybe 3″ of total penetration.  Which pretty much lines up with a study I read a while ago from (can’t remember, was it Fackler, or MacPherson, or Roberts?) where the author tested and determined that impacting a bone caused a drop of somewhere around 2″ of a bullet’s potential penetration.  Can’t find that study, I’ve googled and tried to wrack my brains to remember where it was, so if any of my good readers out there know of it and can point me to it, I’d be glad to update this article with a link to it).

Edited 1/28: Finally found a link to what I’ve heard referred to as “The Canadian Study.”  This was a 1994 study done by the Canadian Police Research Centre, wherein they tested 9mm and .40 S&W ammo as a potential replacement for their .38 Special duty revolvers.  In this test, the CPRC fired about 18 different types of ammo from 9mm, .40, and .38 Special into calibrated ballistic gel — with bones in it!  And without, too, but the key point here is — they used bare gelatin, and they also used gelatin with pork ribs embedded in it.  They used standardized testing procedures, and they tested in controlled environments, and they used the same ammo and the same guns, with the only real difference being the presence of pork ribs.  Now, I said before, using pork ribs isn’t really a good idea since they’re not living, they’re not hydrated like living tissue would be, but — heck, it’s another data point, so why not look at their results and see what they got?  The report is 90 pages long, but I’ll boil down the essence of it for you:

.38 Special hollowpoints penetrated 21.8% DEEPER after passing through bone, than they did in bare gel.

9mm hollowpoints from a 4″ barrel, penetrated average of 10% DEEPER after passing through bone, than they did in bare gel.

9mm FMJs from a 4″ barrel penetrated 20% LESS after passing through bone (23.075″) than they did through bare gel (29.1″)

.40 S&W hollowpoints from a 4″ barrel penetrated an average of 4% LESS after passing through bone, than they did in bare gel.

.40 S&W FMJs from a 4″ barrel penetrated 3% DEEPER (29.45″) after passing through bone, than they did in bare gel (28.575″)

So, what can we draw from this study?  Bone doesn’t make a whole heck of a lot of difference.  Sometimes it actually makes bullets penetrate deeper (attributable to the bone impairing the bullet’s expansion; in the 9mm rounds the bullets in bare gel expanded to an average of .614″, the bullets that hit bone expanded to .593″).  And sometimes, the bone slows the bullet down a little (the .40 S&W’s penetrated about 4% less).  But in both cases, it amounts to a whole lot of not much, wouldn’t you agree?  It’s certainly not the impenetrable Great Wall Of Bone that seems to be a common misconception.  And while we can’t take this Canadian study as gospel (because, again, living human bone is not the same as dead pork ribs), it at least gives us another data point, and all the data points we can find all seem to be pointing to the same conclusion: bones don’t affect bullets all that much.

So that’s my conclusion.  Hitting a bone does rob the bullet of some potential penetrating energy, but not nearly so much as people seem to think.  And if you’re using bullets that have been tested and proven to exceed the minimum 12″ penetration depth, it should still have more than adequate penetrating capability to reach the vital organs and shut down your attacker.  And, now you can see and better understand why the minimum required penetration depth is 12″ as recommended by the Wound Ballistic Conferences of 1987 and 1993 — because, frankly, to get to the vital organs of any attacker, it’s almost certain that your bullet is going to have to go through bone (ribcage or skull) to get there.

Now, I know that people would rather see this demonstrated, than read a 4,000-word discussion of it, and I agree — I think it would be an interesting test to run and I’d gladly do it, but — how do you come up with several dozen embalmed human ribcages to test on?  I’ll supply the bullets and the ballistic gel, if someone wants to set me up with a couple dozen embalmed human cadaver ribcages!

Since finishing and posting my article on overpenetration, and why so much of the worry about overpenetration is simply overblown, it’s brought me back to the subject of full metal jacket bullets (aka “FMJ’s”, usually used strictly as “range ammo” or “training ammo”).

FMJ’s For Self Defense?

FMJ’s are not generally recommended for self defense purposes, as they’re really rather ineffective as compared to modern hollowpoint ammo.  An FMJ is really just a hunk of lead, sheathed in copper; when it hits a target it pokes a hole in the target, and that’s really about it — there’s no expansion, no big temporary wound cavity to speak of, it’s pretty much the simplest and least effective bullet design for causing wounds.

Now, don’t get me wrong, FMJ’s can certainly kill, and they can cause critical hits if they happen to hit the central nervous system or a major artery or the heart.  It’s not like an FMJ won’t do damage, it will, it’s just that — well, just about any other kind of bullet will do more damage than an FMJ would.  The FMJ is the least damaging type of projectile in common use.  A wadcutter is a much more effective wounder than an FMJ, and a hollowpoint can be a significantly superior wounder than an FMJ (assuming, of course, that it penetrates deeply enough).

That’s where FMJ’s excel — penetration.  Because they’re basically a round-nose, slippery design, they present a very low-drag profile and they slip through tissue (or air or water or whatever) easily.  And because they slip through tissue so easily, FMJ’s present a very real prospect of overpenetrating.  Even in a relatively weak caliber like .380 ACP, an FMJ will easily be able to penetrate 22 to 25 inches of ballistic gelatin — and anything over 18″ is considered an overpenetrating bullet.  That’s another reason why, in contrast to some other terminal ballistic experts, I consider FMJ’s a poor choice for the .380 — they provide weak wounding and high overpenetration dangers.  They’re unquestionably a better choice than an underpenetrating bullet would be, but I’d much, much rather use a properly-engineered hollowpoint that penetrates deeply and avoids overpenetration and has an aggressive wounding profile, than use a slippery little FMJ that will sail right through the attacker, causing minimal damage as it goes, and still presents a potentially significant threat to anyone behind the attacker.

How much of a threat is an overpenetrating FMJ?

Let’s consult Charles Schwartz’s excellent Quantitative Ammunition Selection to find out.  In my previous article I had demonstrated that a good .380 or .45 ACP hollowpoint, after penetrating through 9″ of an attacker’s torso, wouldn’t likely have enough residual velocity to even break the skin of a person standing behind the target.  Even if the bullet overpenetrated, it would still have enough energy to cause a nasty bruise, sure, but it wasn’t likely a significant risk to still be lethal; the journey through the attacker’s body would slow the bullet down below 300 feet per second, rendering it unlikely to be able to even break skin.  Applying the same formula and calculations to an FMJ, we get very different results — frightening results.  A 90-grain .380 ACP FMJ, for example, would travel at about 900 feet per second from the muzzle.  After penetrating through 9″ of muscle tissue and exiting out the other side, it would still be traveling at 385 feet per second — and that’s enough to penetrate almost 8.75″ of ballistic gel!  And that means that while it doesn’t exceed the FBI/IWBA minimum 12″ penetration depth, it could still easily cause serious damage or even possibly a fatal hit on a bystander.

Of course, the story is much worse with the .45 ACP FMJ.  Using a 230-grain projectile at 850 feet per second from the muzzle, it’d penetrate through that 9″ torso and when it overpenetrated it’d still be going 498 feet per second.  That would give it enough energy to be able to penetrate over 16″ of ballistic gel, definitely capable of a fatal hit.  But let’s put it in perspective — let’s say that the .45 ACP FMJ penetrated through the 9″-thick attacker, and continued on to hit a bystander — at 498 feet per second, it’d have enough energy to easily pass completely through 9″ of bystander, and still be going at 252 feet per second!  After exiting the bystander, it’d still maintain enough energy to reach almost 8″ deep into ballistic gel — again, far enough to cause serious damage, and depending on where it hits, it may even cause a critical/fatal hit on a person behind the bystander behind the attacker.  Yes, one .45 ACP FMJ could pass completely through two people and lodge deeply enough in the third to cause a fatal hit.

Is overpenetration a concern?

Yes, but it’s only a significant concern if you’re foolish enough to load your defensive weapon with FMJ bullets instead of hollowpoints.  If hollowpoints are legal for self defense where you live, USE THEM.  They’re much more effective wounders, they’re much more likely to stop an attacker, and they vastly minimize any risk of overpenetration.  A hollowpoint expands so large that it slows down dramatically while it’s traveling through the attacker’s body; even if it overpenetrates it’ll be going so slowly that it won’t be nearly as dangerous as an FMJ would be.  The only time I’d recommend against hollowpoints is when you’re using a tiny caliber (specifically .22LR, .25 ACP, or .32 ACP) where there just isn’t enough energy available to push a hollowpoint deep enough to cause a critical hit — in those cases, you have to go with a non-expanding bullet; wadcutters would be preferred, but use FMJ’s if you can’t get wadcutters.  And in .380 ACP, careful ammunition selection is vital — some hollowpoints grossly under-penetrate and can leave you at risk; you have to choose a hollowpoint that penetrates deeply enough to have a chance of causing a critical hit, while minimizing the risk of overpenetration.  See my articles on the .380 Ammo Quest for test results on ammo that can achieve this goal.  And for any caliber more powerful than .380 (such as 38 Special, 9mm, 10mm, 357 Magnum, 357 Sig, 40 S&W, 45 ACP, or 45 Colt) there’s no question — for safety and effectiveness you should be using hollowpoints, and avoiding FMJ’s, for defensive purposes.

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.