5.56x45mm Versus 7.62x39mm
BY Herschel Smith
8 years, 4 months ago
The never-ending caliber debate can be tiresome, but then again occasionally there are good and useful additions to the body of knowledge. Because of my son being deployed, I have always known and understood (not first hand, but second hand) the utility and superior performance of the 5.56mm in the field (and when I say “field,” I mean Fallujah, not your local shooting range where your know-nothing, tacticool weekend warrior waxes stupid in front of everyone).
I have also heard from his teammates about being shot by the 7.62×39. Specifically, Corpsman Prince gave me details of his experience.
He was very kind and friendly, well trained, in excellent physical condition, and had absolute commitment to his fellow Marines. He showed me his wound from Iraq within several days of returning. A round from an AK-47 had entered through the front part of his lower thigh, ricocheted up his thigh, and exited out of the very upper part of the back of his thigh. Entry and exit wounds (now scars) were at least a foot apart.
Corpsman Prince stayed in Iraq and did his own rehabilitation during the deployment. The hardest thing about the experience, he told me, was getting enough pairs of clothing after each successive pair became blood stained. The more interesting thing about what happened that day with Corpsman Prince was what happened to his fellow Marines. He wasn’t the only one who was wounded in that engagement. Several other Marines were also wounded, and Prince had to treat them before he could treat himself. He did so while bleeding out.
The exit wound was small, virtually as small as the entry wound (if the scar is any indication of the wound size when it happened). The scars I saw were identical in size.
But the specific addition I wanted to mention has more authority than anything I can muster. It comes via Defense Review, from Tacmed Australia. I will quote at length, and then offer up a disagreement and an agreement.
Admittedly I’d rather not be shot with either, but if I had to choose, I’d take a round from the AK47 over the M4 any day of the week. To understand why, it’s important to have a very basic look at the physics behind terminal ballistics, in this case being the science of what happens when a penetrating missile enters a human body. The first place to start is the Kinetic Energy Equation:
KE = ½ M (V1-V2)2
Breaking this equation down into its components, we have Kinetic Energy (KE) influenced by the Mass (M) of the penetrating missile, as well as the Velocity (V) of the missile. This make sense, and it is logical that a heavier, faster missile is going to do more damage than a lighter, slower missile. What is important to understand is the relative influence that Mass and Velocity have on Kinetic Energy, as this is key to understanding why I’d rather be shot by an AK than an M4. You’ll notice that the Mass component of the KE equation is halved, whereas the Velocity component is squared. For this reason, it is the Velocity of the projectile that has far more bearing on the energy that it dissipates into the target than the mass. The V1-V2 component of the equation takes into consideration that the projectile might actually pass straight through the target, rather than coming to rest in the target. In this instance, the change in the Velocity of the projectile as it passes through the target (V1 being its velocity as it enters, and V2 being velocity on exit) is the factor that is considered when calculating how much energy the missile delivered into the target. Naturally if the projectile comes to rest in the target (ie: no exit wound) then V2 equals zero and the projectile’s velocity as it entered (V1) is used to calculate the KE.
That’s enough physics for now, but you get the concept that the optimum projectile to shoot someone with is one that has a decent mass, is very, very fast, and is guaranteed to come to rest in your target, as to dissipate as much energy as possible into them, and hence do maximal damage.
The next concept to grasp is that of permanent cavitation versus temporary cavitation. Permanent cavitation is the hole that gets left in a target from a projectile punching through it. You can think of it simply like a sharp stick being pushed through a target and leaving a hole the diameter of the stick. The permanent cavity left by a bullet is proportionate to the surface area of the bullet as it passes through the tissue. For instance, if a AK47 round of 7.62mm diameter at its widest point passes cleanly through a target, it will leave a round 7.62mm hole (permanent cavity). If this hole goes through a vital structure in the body then the wound can be fatal, however if the bullet passes through soft tissues only then the permanent cavity can be relatively benign. This is a slight oversimplification of the concept, as bullets will rarely remain dead straight as they pass through human bodies, as they have a tendency to destabalise, and for the heavier back end of the bullet to want to overtake the front. This concept, known as yaw, increases the frontal surface area of the bullet as it passes through tissue, and hence creates a larger permanent cavity.
Here is my disagreement so far. I’m not certain that the author understands the distinction between cavitation and creating a cavity (or perhaps it is that he isn’t clearly delineating the difference). Cavitation has to do with the formation of voids due to change of state of a liquid to a gas, whereas some of what he is discussing has to do with the yawing and fragmentation of the 5.56mm round in tissue. There are both of these effects at work.
We’ve discussed the rocking back and forth in flight that occurs with the 5.56mm round, based on the very well researched paper Small Caliber Lethality: 5.56 mm Performance In Close Quarters Battle. This rocking back and forth during flight, which occurs even with boat tail 5.56mm, causes rapid yawing when it enters tissue. Fragmentation ensues, ensuring multiple fragments take different trajectories through tissue. This may be what the author is referring to when he mentions permanent cavity. Or then again, he may be referring to the high velocity of the 5.56mm round, and as I said above, both effects are at work.
But by mentioning Newtonian physics, he is on to something. It’s not only the energy of the projectile that’s important, but the velocity term is a function of the exit velocity, which means that it’s also important how much energy gets deposited in the object. If the bullet doesn’t stop, fragment, or otherwise leave its energy in the object, it will not do as much damage as one which does. It’s the same way with, for example, radiation. A high energy gamma (e.g., from N-16) can pass through a piece of tissue without ever interacting with orbital electrons and ionizing atoms. Thus, high energy photons can pass through a body without causing dose, depending upon depth, energy, etc.
In order to demonstrate the point, he provides two videos, one of 5.56mm in ballistic gelatin, and one of 7.62 in ballistic gelatin. But the most impressive thing the author does is convey his own experience treating wounds from 7.62 mm and 5.56 mm rounds, and then show you what an X-ray looks like of an upper thigh and femur that has been hit with a 5.56 mm round from a couple of hundred meters.
As I said, this was from a couple of hundred meters. Ponder on that a bit. While this article doesn’t specifically address the .308/7.62×51, some of the principles are applicable.
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On November 30, 2015 at 12:20 am, kurthofmannstlgunrightexaminer said:
“You’ll notice that the Mass component of the KE equation is halved, whereas the Velocity component is squared.”
I have to quibble with that. The half applies to everything it multiplies, including the velocity. Yes, the velocity is squared, and the mass is not, and that makes a big difference, but the energy equation could just as easily–and as accurately–be written this way:
KE =M * ½ (V1-V2)2
On November 30, 2015 at 12:45 am, Herschel Smith said:
I just quoted. I didn’t endorse.
On November 30, 2015 at 12:47 am, kurthofmannstlgunrightexaminer said:
Understood. Didn’t mean to imply otherwise.
On November 30, 2015 at 12:51 am, Herschel Smith said:
Got it. One could easily imply taking half of the square. The point [he made not have made] is that the velocity component is still squared. If you isolate the terms, one is linear, the other is squared. That’s their relationship. He probably shouldn’t have said it like that. It’s confusing to readers.
On November 30, 2015 at 12:53 am, kurthofmannstlgunrightexaminer said:
Precisely.
On November 30, 2015 at 12:38 am, Daniel Barger said:
A large part of what happens isn’t just bullet weight and velocity but design. Virtually ALL 7.62×39 ammo used against US Forces is FMJ. Such ammo is far more likely at ranges under 200 yards to
pass through soft tissue without expansion and often without yawing or keyholing. That’s just the nature of typical FMJ. NATO 5.56 is designed to break up, to successfully break up requires that the small round be moving very fast. Even so there is no guarantee that the round won’t pass clean through a body….in Somalia against asthenic underfed opponents many a serviceman reported shooting a skinny and watching them run off.
US forces need to abrogate the agreement limiting us to specific ammo types and use whatever works best for the theatre of operations….if that is HP ammo so be it.
As an aside the 5.56/.223 is illegal for taking deer in many, perhaps most states whereas the
7.62AK round is not, with the proviso that SP/HP ammo is used, not FMJ. If 5.56 was so much
more effective against people it would be logical to use it against deer, an animal similar in size and weight to adult men.
Neither round is actually ideal for combat. Both are tradeoffs made to allow a serviceman to
carry more rounds on patrol.
As for the x ray of damage done by a 5.56 round……I’ve been radiographing people for nigh on 40 years. I’ve seen the same level of damage from 45ACP.
On November 30, 2015 at 12:46 am, Herschel Smith said:
But what you haven’t seen is that damage caused by a 45ACP at 200 meters. As for FMJ (or MC), the video isn’t of FMJ ammunition. It’s soft point. The points apply to soft point as well as FMJ or MC.
On November 30, 2015 at 7:08 am, Lina Inverse said:
NATO 5.56 is designed to break up
Not designed to do this, it just fortuitously turns out to be the case for conventional FMJ rounds. It’s wounding mechanism of breaking at the cannelure, and the rear part further fragmenting, all depending on the velocity when its impacts, was only elucidated by Dr. Martin Fackler in the 1980s. And it’s important to emphasize the velocity requirement, for every inch you chop off the standard 20 inch barrel reduces the effective range by 50 yards.
On December 1, 2015 at 2:45 pm, Archer said:
As an aside the 5.56/.223 is illegal for taking deer in many, perhaps most states whereas the 7.62AK round is not, with the proviso that SP/HP ammo is used, not FMJ. If 5.56 was so much more effective against people it would be logical to use it against deer, an animal similar in size and weight to adult men.
Remember that the people who write laws tend to know little-to-nothing of firearm function, ammunition specifications, or even elementary physics.
That said, it’s my belief that many (if not most or all) of those caliber laws are in place to prevent people from wounding (but not killing) deer with severely-underpowered .22LR rounds. Depending on how it’s written, 5.56/.223 rounds may or may not fall under such a ban; if the law is bullet-diameter-specific, 5.56/.223 is out of luck, but if it’s muzzle-velocity- or kinetic-energy-specific, a good .223 is OK. (Oregon, for example, allows rifles of .22 cal. or larger for deer, but no rimfires [centerfire only] or military/FMJ rounds. Thus, 5.56/.223 SP/HP is allowed, but the rimfire ban precludes .22LR.)
On December 5, 2015 at 12:42 am, sootsme said:
Out in the Pac Northwest rain forest, once the ol’ timers have a snort or two, they’ll tell you that more game has been taken by .22lr than all the rest combined, at least in that part of the world. This at ranges up to ~100 yards. Not an endorsement, just a little history regarding “common sense gun control”… your mileage may vary…
On November 30, 2015 at 4:11 pm, Phil Ossiferz Stone said:
/rereads article and accompanying commentary twice
Okay, who hunts?
Okay, which hunters prefer a fragmenting bullet that stops inside the animal to one that punches a full-caliber hole (or better) all the way through, and lets a lot of blood out and air in?
Okay, which hunters would abandon the latter in favor of the former in any kind of battlefield or self-defense scenario?
Neither would I. (Give me Hornady TAP rounds, please). All this post establishes is that FMJ 7.62×39 sucks and that Marines are tough SOB’s.
On November 30, 2015 at 4:28 pm, Herschel Smith said:
But the video is 7.62×39 soft point, not FMJ. 7.62×39 soft point sucks, and compared, 5.56×45 rules.
On November 30, 2015 at 8:04 pm, Joe said:
Well…the question of 7.62×39 effectiveness whether FMJ or soft point is rather more complicated than a blanket condemnation would imply. See the work of Dr. Gary Roberts … some of which can be found at http://www.ar15.com/content/page.html?id=310
The short and dirty is that the type of FMJ bullet construction (which has substantial manufacturing variation) has a dramatic impact on the effectiveness of the 7.62×39 FMJ round while the best soft point loadings are described by Dr. Roberts as essentially constituting “30-30 light” and having excellent barrier penetration capability.
Dr. Roberts has done comparable research and testing on basically all standard military rounds both U.S. and Russian … his findings make very interesting reading for all those interested in the topic and I would highly recommend they be considered (try Googling his name or internet handle which is DOCGCR) …. his work was archived at M4Carbine.net for a long time but I believe is now scattered about on various other sites…one of which is AR15.com…
On December 1, 2015 at 12:42 am, TSA_TheSexualAssault said:
The Russians/Soviets understood the advantages of a .22 high velocity round and developed the AK-74. AK-47 weapons shipped to the Africa and USA for cash. Still work fine, and monkey-simple to use.
On December 1, 2015 at 1:51 am, Pat Hines said:
Both math and experience in one article, bravo.
On December 1, 2015 at 7:25 am, nighthawk said:
As a combat veteran of Vietnam , let me say this: the 5.56 doesn’t penetrate brush and go on to it intended target. The 7.62, and even the .30 carbine will. Again this is my experience with a number of weapons in ‘Nam. I have no experience in desert type fighting. ( I do have experience in long range hunting) From my experience I will take almost any caliber over the 5.56. But everyone has their opinion and preference, as they should.
On December 1, 2015 at 9:23 am, WalkingHorse said:
Gents, it appears the above equation is incorrect if it really is intended to describe the energy deposited into the target. I can make sense of it in one case, where the projectile loses no mass during impact and leaves the target with velocity V2. The square term is misplaced, and should be applied to the initial and final velocity directly.
On December 1, 2015 at 11:51 am, Herschel Smith said:
This is a GREAT comment! You are correct. I copied and pasted, but taking the velocity and placing it inside the parenthesis (V1-V2)^2 is not correct for any condition or purpose. It’s mathematically incorrect. Think of it as calculating the kinetic energy entering, in which case it would be V1^2, and kinetic energy exiting, or V2^2, and subtracting the two.
Thanks for making the observation.
On December 1, 2015 at 12:10 pm, WalkingHorse said:
My pleasure, sir.
On December 1, 2015 at 12:41 pm, Joel QC said:
Is there really a difference between 7.62x51mm FMJ and 7.62x39mm FMJ? Unless its the old school West German ammo that acted like a big varmint round anyway.
I know, I know, physiology is nothing similar…but I have guided hunters whose magnum caliber (300WM) bonded bullets failed to expand on smaller whitetails at close range and the wound cavity looked like pencil stabs.
Throw some SP or HP in the works though and THERE you see a difference!
On December 1, 2015 at 5:13 pm, Lt. Greyman, NVA said:
A cherrypicked x-ray means nothing. Similar ghastly wounds were found from the genco Action Safety Round in 9mm (a French Product).
The point is that field experience shows that the .223 just plain sucks when it comes to stopping. In the Book, “BlackHawk Down” the author cites soldiers complaining that the round “just would not put them down even after 6 or 7 hits” and the the soldiers were “crowding around” the guys who had M14’s because they were reassured by the one shot stops. The .223 is plagued by stories like that. Not so the .30-06 or the .308.
In the civilian world, .223 has shown to be a poor stopper, with Randy Weaver taking a midline hit (which exited out of his armpit and he only noticed later!) and numerous other examples.
The .223 is a varmint round, not even legal for hunting deer sized game in most states because experienced hunters know that the round will not make a clean kill on normal sized game, and that is before you geld the round by firing it out of short barreled M4 (14 inch) or (even worse) a 7 inch “pistol”. The fact that it is FMJ just worsens that stopping situation. Everybody is looking for a replacement, from the .300 Blackout guys to the 6.8 Remington guys to those who would have us adopt the 7.62 x 39 outright.
There is an argument to be made that the 10mm round with full power ammo (like Underwood’s 135gr JHP) is superior to a .223 in both a 14 inch barreled Subgun (2050fps/1220ft/lbs) as well as a 6 inch pistol barrel (1600fps/800ft/lbs). The 223 only makes 600ft/lbs in a 7 inch barrel and less than 1000ft/lbs in a 14 inch M4 and you can’t carry it in a pistol!
On December 1, 2015 at 5:29 pm, Herschel Smith said:
“The point is …”
That’s not my point at all. That’s your point, and it isn’t your article, it’s mine. I understand your points though. Someone who comes in predisposed to hate the 5.56 will leave hating the 5.56 because … just because.
As for “Everyone is looking …,” “Everyone” is not doing anything. Everyone is no one. “Everyone” is an exaggeration when you don’t know what else to say.
On December 1, 2015 at 9:43 pm, Adam Sanchez said:
How sad. Lt. Greyman, NVA, made some good points. At least attempt to refute what he says.
Personally, I’m a big fan of 5.56/.223, but I realize it’s limits.
I have to agree. .300, or 6.8, are more effective man-stoppers. No need to “double tap” when rocking those calibers. No need for Mozambique Drills. ;-p
On December 1, 2015 at 10:03 pm, DAN III said:
Adam,
I’ve become a big fan of 300 Blackout. One of the reasons being it’s accurate performance in a short barrel, i.e., 8-9 inches using a 4x scope. I have hit 18″x24″ (combat effective zone) steel @ 200 yards easily out of an 8″ Noveske upper with 110 grain Noslers.
For my purposes the 300 BLK is a great trunk gun, highly concealable in it’s 8-9″ barrel length pistol configuration.
In essence what one has with 300 BLK/AAC is the 7.62x39mm in it’s Blackout iteration of 7.62x35mm.
But if push-comes-to-shove/SHTF, the 5.56mm will be my weapon of choice, simply because of the ammunition availability.
On December 2, 2015 at 12:22 am, Adam Sanchez said:
I agree. 5.56/.223 for the availability.
On December 1, 2015 at 10:19 pm, Herschel Smith said:
I have no desire to refute him or anyone else. I made the points I made and don’t need to do anything else. Look, I don’t mind disagreement with anything I say. But I was accused of “cherrypicking” data (or linking someone who did), and then he proceeded to cherrypick data and give me anecdotal evidence rather than data from the field.
His comment was a childish outburst and tantrum, not something that warranted a refutation.
On December 2, 2015 at 2:57 pm, Lt. Greyman, NVA said:
Data on 10mm is published by Underwood. I cited published works in my argument with quotes from known book sources. I used Ballistics by the Inch site for .223 energy. Not anecdotal.
On December 2, 2015 at 2:37 pm, Lt. Greyman, NVA said:
I care not one whit if the .223 is wonderful or not, hated or not. I care about facts, as do the men in combat. Combat is a crucible which burns away pretensions. In combat the .223 is not trusted by the men who use it.
On December 2, 2015 at 3:21 pm, Herschel Smith said:
Then offer up salient points and data in an objective, clinical manner instead of screaming opinion. You don’t know that the 5.56 isn’t trusted by the men who use it. You just made that up. I personally know many of them who do. Don’t speak in broad platitudes and with sweeping statements that add nothing to the discussion. See Joe’s comment above. I don’t require that everyone agree with me. I require that people not be a jerk.
On December 2, 2015 at 2:52 pm, Lt. Greyman, NVA said:
1. I never said “the point is”.
2. It is your article and I would never try to take it away from you. I saw the comments section and thought it was a invitation to comment about the subject.
3. I will do better next time. I apologize to “everyone” as I forgot to mention the 6.5mm Grendel guys as well as the Army itself (See: http://usacac.army.mil/CAC2/MilitaryReview/Archives/English/MilitaryReview_20120831_art004.pdf )
On December 2, 2015 at 3:22 pm, Herschel Smith said:
Educated comments are not the same thing as shouting sweeping judgments that are too easily falsifiable.
On December 2, 2015 at 6:25 am, Lina Inverse said:
To the extent the men in BlackHawk Down were using 5.56 NATO rifles with 11.5 inch barrels they might not have been achieving sufficient velocity for their rounds to break at the cannelure, or have the back half further break up. The stopping power of conventional 5.56 NATO FMJ rounds does depend on an unplanned, undesigned, and not even understood until the ’80s “trick”, so it is marginal, which we can see the Army and Marines implicitly acknowledging with their new bullet designs.
On December 1, 2015 at 9:37 pm, Adam Sanchez said:
*Yawn*
How silly. This conversation is getting old like the .45 vs 9mm debate that permeates so many gun forums online.
Look, here’s the deal: Sure. I’d rather get hit with some Iraqi/Syrian/Afghani Insurgent’s, nasty, 20 year old, Tula FMJ in 7.62×39, than what I shot during OIF. But you know what?!? I GUARAN-*damn*-TEE that you wouldn’t want to be hit by Silver Bear SP, Wolf Army Standard HP, Hornady Zombie Max, Hornady V-Max, or Hornady SST in 7.62×39. Youtube it…. ;-p Nasty wounds with effective knock-down.
Guys, I’m sorry, but technology is changing how we view “standard” milspec ammo. Not everyone in the world shoots straight up ball. Last I checked, the Geneva Convention didn’t apply to my stash at home.
On December 1, 2015 at 9:47 pm, DAN III said:
Adam,
“How silly. This conversation is getting old like the .45 vs 9mm debate that permeates so many gun forums online.”
You took the thoughts right out of my head. Same as the .45 vs 9 mm debate that not only permeates the internet but has permeated every gun magazine from American Rifleman on up….for the last….umpteenth decades !
For those berating either round….not one is willing to stand downrange and take a round (caliber of one’s choice) for scientific posterity.
No one wants a hole in them….not even from the lowly 22lr.
On December 1, 2015 at 10:22 pm, Herschel Smith said:
You’re being ridiculous. If you don’t like the subject, don’t read it or don’t comment. It pertains to information concerning ballistics and ammunition. That qualifies as a legitimate subject for my web site. I make that decision, not you. The fact that it may be controversial is irrelevant to me. Have you ever read this or similar websites before? Since when does the fact that something is controversial disqualify it from being discussed?
On December 2, 2015 at 7:12 am, DAN III said:
Mr. Smith,
“Since when does the fact that something is controversial disqualify it from being discussed?”
Controversy is good. It makes one think. It exercises the mind.
Thanks for your interesting essays.
On December 2, 2015 at 12:25 pm, eatgrueldog said:
And check this out: ”
It is common for proponents of light and fast arrows to counter that
the faster arrow will have traveled a greater distance through the
tissues in the same time period than will the heavier, and slower, arrow. This would be valid were it not for the nature of resistance forces.
As the arrow’s velocity is increased the resistance does not increase equivalently. The resistance increases exponentially. The resistance of a medium to penetration is reliant on the square of the object’s velocity (assuming objects of a given coefficient of drag; i.e., using arrows with the same external profile, material and finish). In other words, if the arrow’s impact velocity doubles, the resistance increases by a factor of four. If the impact velocity quadruples, the resistance to penetration increases 16 times!”
I know he is talking arrows, but the resistance will still hold true. More resistance at bullet speed instead of arrow speed says more damage and larger wound channel to me
On April 22, 2018 at 9:06 pm, Georgiaboy61 said:
@ JoelQC
Re: “Is there really a difference between 7.62x51mm FMJ and 7.62x39mm FMJ?”
The former is a full-bore, full-power center-fire rifle round, whereas the latter is an intermediate round designed to fill the ballistic niche between battle rifles on one hand, and weapons utilizing handgun ammunition, such as pistols and submachine guns.
Typically, intermediate rounds are designed to be used in battle carbines (assault rifles), such as the AKM/AK47 family of weapons. Intermediate rounds trade some muzzle velocity and hence, long-range performance, in return for a smaller, lighter projectile fired from a case which is typically shorter and less-voluminous than a full-sized rifle cartridge case. Since an intermediate cartridge holds less propellant, it generates less recoil when fired and is therefore more-controllable on fully-automatic fire in comparison to full-blown rifle cartridges (which are often difficult if not all-but-impossible to control on full auto).
The 7.62×51 NATO round is 12mm longer than the 7.62×39 round. M80 Ball (FMJ) 150-grain ammunition typically has a muzzle velocity of ~ 2805 fps when fired from a 20-22 inch barrel, whereas 7.62×39 123-grain FMJ typically leaves a 16-180-inch muzzle at ~ 2350-2400 fps.
The 7.62×51 M80 Ball round is typically supersonic (and thus effective) out to 1,000 yards under most environmental conditions; my ballistic solver shows that M80 @ 2805 fps goes subsonic at 1058 yards, a distance at which it still packs 412 pound-feet of force. 7.62×39 124-grain FMJ leaves the muzzle at 2350 fps, and goes subsonic at 601 yards, at which time it has 346 pound-feet of energy. By way of comparison, the M80 rifle round is moving at 1662 fps with 919 ft.-lbs. of energy at 600 yards.
Assault rifles are optimized for select-fire use with the typical range envelope of modern combat, i.e. 0-300 yards (meters), with an absolute effective range in the 600-800 yard range (depending on load, MV and other factors), whereas a traditional full-power military battle rifle cartridge functions optimally out to 800 yards, and remains potent within the range envelope of 0-1200 yards.
Clearly, these are different types of cartridges and different types of weapons, designed for somewhat different roles and missions.
On June 7, 2018 at 8:07 am, lsume said:
The point made about fighting in Vietnam and the projectile not penetrating bush is logical. However, fighting in the desert is a different theater of combat. The tumbling effect of the 5.56 is far more damaging than the thru and thru. One of two cousins that are retired police officers now carried different hand guns. The one who carried a 44 magnum and I went round and round about his choice. In those days, he carried what was a standard load 44 mag. I would argue with him that a great deal of the energy he packed was still in the projectile after it penetrated his intended target. He could never understand my logic. My concern was for the potentially innocent bystander that could get hit by the projectile after it penetrated the target. As I recall, his 44 mag ammo was a full metal jacket over a standard lead projectile. As I recall, he was not using hollow points back then. The tumbling effect of the 5.56 makes that rifle at relatively close range extremely severe to the target. As a retired mechanical engineer I am very familiar with kinetic energy and have done the calculation very many times. One of the contributors to this discussion made an excellent point when subtracting the remaining energy in the projectile after leaving the target. A tumbling multifractured round that’s energy is fully absorbed in the target is far more lethal than the projectile that stays in tact and fully penetrates the target in my opinion.