Muzzle Velocity vs FT LBS

[robert1811]

its a pretty common conception that when it comes to self defense a rifle bullet vs a handgun bullet, the rifle is always superior for stopping power.

This is leading me to question why that is, and what to look for when looking at a velocity chart (which also lists grains etc. im looking at ballistics101.com) when it comes to stopping power.


A 223 which is 50 grains (im looking at Corbon FMJ) is moving at 3000 FT/sec with 1099 Ft/lbs of energy.

I have seen what this round can do from brassfetcher on youtube and it is devasting.

Now, in the handgun realm im talking big bore here, 44mag and the 460 magnum (I recently bought a 44 mag and a book on big bore revolvers!)

So im looking at Buff Bores 44mag, 270 gr. ft/sec of 1450 and ft/lbs of 1260

And

Buff Bores JFN 300gr, ft/sec 2060 and ft/lbs 2826

Obviously the 460 crushes the 223 and 44mag in terms of both catergories and weight. I thought I throw it in there to show that handgun velocities can get fairly close to rifle velocities. But I feel the 44mag is comparable with the 223 when speaking of lower velocity rounds in both catergories (and in someways trumphs the 223 IMO).

So why is the common saying that a rifle round has better stopping power than a handgun round? The 223 is lighter, travels faster but has almost the same ft/lbs'. The 44 is heavier travels slower but hits with greater ft/lbs.

Please do not post overpenetration is why 44 mag is a worse choice or that a 460 has extreme recoil and is the worse choice. That is not what this question is about.

I am truly curious, why and what should you be looking at when it comes to stopping in power (IMO the damage done) in terms of ballistics? What is the determining factor? Is ft/lbs or energy and or bullet weight a greater determing factor or is ft/sec?

[robert1811]

Edit

Obvoiusly there a heavier rifle choices out. I wanted to use the 223 to illustrate how devastating a non traditional hunting round can be but also how close a handgun round can be when meeting it. It wouldnt be fair for me to compare handgun rounds to each other because the weights,velocities, and ft/lbs are all relativly similar when looking stopping power results in .40 .357 45 acp. 10mm and 9mm, which is the premise of my rifle handgun question.

[Aguila Blanca]

Size of wound channel.

[jnichols2]

A very large handgun can indeed be more devastating than a small rifle.

The energy is a good indication of a round's effectiveness..

However; a hollow point round will normally be more devastating than a similar full metal jacket (FMJ). It will expand and make a larger hole than a FMJ.

The .223/5.56 has a design that sets it apart.
It tends to make a small hole like a FMJ in hard objects. But with sufficient velocity it will "tumble" in soft objects.

This tumbling effect can create truly horrible wounds.

Any explanation of how they designed the round for this tumbling effect must be directed to someone much smarter than I.

[carguychris]

Originally Posted by robert1811

Is ft/lbs or energy and or bullet weight a greater determing factor or is ft/sec?

This is the classic Big Slow Bullet vs. Small Fast Bullet question that has been debated over and over again ever since the advent of smokeless powder in the late 19th century. (With black powder, the Small Fast Bullet generally isn't a viable option.) There isn't One Correct Answer; if there was, the debate wouldn't have continued.

Originally Posted by Aguila Blanca

Size of wound channel.

Also...

Recoil and recovery for follow-up shots; the Big Slow Bullet generally has more recoil, making recovery more difficult.

Bullet drop and energy retention at very long range; the Big Slow Bullet generally has more of both, assuming the ballistic coefficient is the same, which it usually isn't. (FWIW using the two cartridges the OP initially discusses, .223 is the clear winner in this regard, as its ballistics are far superior due to the generally long, slender, and ballistically efficient bullet.)

Wear on the firearm. The Big Slow Bullet tends to shake things apart due to the higher recoil, but generally does not erode the bore as quickly.

Weight and cost of ammo. This is one comparison where the Small Fast Bullet is almost always the clear winner, which is why military cartridges have generally become smaller over the last century. A soldier can carry more cartridges if they're smaller, so he can fight longer without needing to be resupplied. OTOH this is less important for SD or hunting. Most SD encounters involve 2-4 shots and very few involve more than 10. Few hunters fire more than a couple dozen shots before returning to camp, and the handful of common hunting tactics that involve high round counts are usually performed from a fixed position where the ammo can be staged beforehand (e.g. prairie dog shoots), rather than having to be backpacked in.

[Brian Pfleuger]

Complex question.

There's a lot to it.

First of all "stopping power".
I really wish that term would drop off the face of the earth. If there's anything to "stopping power", beyond destroying the CNS, it comes from hydro-static shock. Hydro-static shock comes purely and totally from speed. A wider bullet at speed may produce more Hydro-static shock than a narrower bullet at speed but neither will produce any at low speed. Virtually no handgun round is fast enough to reach the minimum speeds required (about 1,800fps minimum) to produce Hydro-static shock. Some will get there, yes, but at what cost? The blast, recoil, follow-up shots, gun weight, everything is nuts in terms of SD.

Kinetic Energy versus momentum.
There's more to life than kinetic energy. Momentum is a big factor. Slow, heavy bullets have a lot of momentum. Momentum can be good or bad. Momentum is responsible for penetration. That's important. Kinetic energy doesn't produce penetration, momentum produces penetration. Penetration is good... isn't it? Maybe, it all depends what's on the other side.
Kinetic energy is what expands the bullet. It takes energy to bend metal.

You say "Please do not post about..." but that's really what it comes down to. A howitzer would be awesome for SD but the recoil and muzzle blast are a big obnoxious, not to mention the recoil and over-penetration.


In any case, the points and opinions can be argued one way or another but what CAN'T be argued is that there's a lot more to it than ft/lbs. That's why ft/lbs is the determining factor in a SD choice.

[JD0x0]

Rifle bullets generally cause much more hydrostatic shock, than pistol rounds. This is why you can turn a deer's heart and lungs, into soup, with a chest shot, rather than just making a big hole through them.

Rifle bullets, with correct weight and construction, for your intended target should pass through, creating a small entrance wound and generally a much larger exit wound. The fact that the rifle bullet is traveling so fast, then expanding creates devastating hydrostatic shock, as it quickly sheds energy. You could potentially kill someone with a high powered rifle without a direct hit to a vital organ. A hit to the shoulder could cause enough hydrostatic shock, to potentially, stop the heart, or rupture blood vessels in the lungs, causing them to fill with blood. Pretty much any pistol round, no matter the caliber, would just make a hole through the spot that was hit. Expanding bullets in pistol calibers tend to just make bigger holes. They shed energy faster so you have a potential loss of penetration (which wont matter if your HP's are passing through the target already)

Generally more speed= more hydrostatic shock. Lighter rifle bullets tend to travel faster, but lose velocity faster. If they are too light, and lightly constructed, there's a chance the bullet could just stop or shatter with the first bone it hits. Heavier bullets have higher sectional densities and ballistic coefficients generally but have a slower initial velocity. This means velocity over a range isn't lost as quickly, and the superior SD causes increased penetration. It's about finding the right bullet weight for the target you intend on shooting. Something smaller like .223 might be a little more picky with bullet weight, since generally bullets are light, and the cartridge doesn't develop a whole lot of energy compared to larger rifle rounds like the .270 which can shoot much heavier bullets at the same velocity as .223

[44 AMP]

This tumbling effect can create truly horrible wounds.

Any explanation of how they designed the round for this tumbling effect must be directed to someone much smarter than I.

I don't know if I'm smarter than you are (probably I'm not), but I do know a few things that apparently, you do not.

ALL rifle bullets tumble. Its because of their shape. The bullet base is heavier than the nose, so after a certain amount of penetration, the bullets swaps ends. The .223/5.56mm round got a huge reputation for this, only because of its small bullet size, combined with the use of a FMJ bullet.

Traditionally, .22 caliber centerfire rifles were always regarded as pest & varmint calibers. The were always loaded with bullets designed to expand as violently as possible (because a bullet holding together for penetration is actually counterproductive when your target is a small animal).

By the early 20th century, the majority of the world's militaries were using approximately .30 caliber rounds (or something between .26 and .32 calibers). These bullets DO tumble after impact. However, most of them do not tumble until after over a foot of penetration of soft tissue. This being the case, the point were a larger bullet tumbles is often after it has exited a person.

This was well known, but not anything of any real importance (or use) until we changed to the very small caliber bullet of the .223. Combining a very small bullet with the military full metal jacket design showed that it begins its tumble after only a few inches of penetration. This does result in larger wounds than if the bullet did not tumble, and was beaten like a cheap drum as justification for using the small bullet (small compared to previous standards).

Oh, and by the way, "truly horrible wounds" are those inflicted on myself, or my friends, only. Wounds inflicted on people I meant to shoot are not horrible, they are efficient.

I am truly curious, why and what should you be looking at when it comes to stopping in power (IMO the damage done) in terms of ballistics? What is the determining factor? Is ft/lbs or energy and or bullet weight a greater determing factor or is ft/sec?

I think you are missing an important point. And that is partly because of the terms we use to discuss these things.

Stopping power? What is that? Its a nebulous idea referring to one round supposedly being better at stopping (a person, usually) than another. And we look at things including size, weight, speed, shape, etc.

And it involves another vague concept, what amount of (the various factors named above) is needed to stop an attacker, without actually killing them. I say this because #1) if you kill them, they are stopped, and #2) the point of a defensive shooting is to stop, not to kill. If the attacker happens to die as a result of being stopped, so be it.

So, we look at what it takes to stop an attack, in terms of energy, or velocity, or some other easily quantifiable factor.

But what is being missed is that it is the placement of the hit, followed by what the bullet does after the hit, that not only matters most, it is the ONLY thing that really matters.

And, to further complicate things, when talking of 'stopping power" one must not include any cases where the attacker, once shot, decided to cease the attack.

What real world results shows us is that any bullet that gets in the right place works. And that above the minimum needed for that there doesn't seem to be a real world effect. Stopped is stopped, and dead is dead.

However, since it is potentially our selves and our loved ones at risk, and because we have a virtually ingrained "more is better" mentality, we tend to opt for more when practical.

The point at which the speed of the impact becomes a factor (beyond what the speed allows the bullet itself to do) is close to 2000fps. It is at around this point that hydrostatic effects do become a factor. Only the largest most powerful handgun rounds approach this level. The majority of rifle rounds begin well above it.

But shock alone rarely compensates for the bullet not going where it needs to go to stop the fight. Blow off a hand with a magnum rifle hit (or an artillery shell) and the attacker isn't stopped, unless they decide to stop (most would, I think, but history is full of examples, usually in war, of guys taking huge wounds-but not instantly fatal, and not stopping).

Stopping power is a very complex idea, and involves, or should involve a lot more than just the physical properties of the rounds used. They are certainly a big factor, but they aren't the only factor that needs to be considered.

[jmr40]

The handgun velocities you are listing are a bit optimistic. While they are obtainable from guns with 8" or longer barrels most people shoot the ammo in guns with 4" or shorter barrels. While a 44 mag might be listed at 1400 fps, 900-1100 fps is much more realistic. Rifle ballistics are taken from 24" barrels and shorter barrels will lose some velocity, but even a 16" carbine length barrel is going to be pretty close to advertised speeds. You'll still get around 2800 fps instead of 3000.

Using energy numbers can be very misleading. It is a good way to compare the effectiveness of rounds that are very similar. If you are comparing 44 mag, 45 acp and 45 Colt the numbers mean something because the rounds are similar. Same with comparing 308, 30-06 and 270. But if you try to use energy numbers as an argument in a 270 vs 44 mag debate they are useless because the 2 rounds kill game, or humans in very different ways.

If bullet impact speed is around 2000fps or faster, you will see a shock effect that puts stuff down much faster than the energy numbers would indicate, especially on smaller animals or humans. You can't get that kind of speed from handgun rounds so they depend on larger diameter, heavier bullets. Both methods work, just in different ways. A 223 soft point at 2700-3000 fps is going to put down a small deer or human fast. But on a much larger game animal the small bullet won't penetrate enough to reach vital organs. That is what the big bore handgun rounds are made for.

The big bore handgun rounds look good on paper. But they are designed to penetrate deep inside game much larger than humans. On a 1,000 lb brown bear they are the ticket. On a human, a 50 gr 223 softpoint @ 2700-3000 fps is the better stopper.

[JD0x0]

Personally, I think bullet tumbling is overrated. Yes it's better than a FMJ simply penciling through your target, but if you have the option to use expanding bullets why wouldn't you? It's one thing if you're only limited to FMJ rounds because you're in the military or something, but no hunters that I know ever try to get their bullets tumbling. They like expanding bullets with enough 'oomph' to leave an exit wound.
I don't think any pistol cartridges can reasonably achieve 2000-2200fps in a pistol, except, the 5.7x28, and 4.6x30 which use extremely light bullets (around 23-31grains) but these are pretty anemic rounds, and likely don't have enough energy to create serious hydrostatic shock in a human or human sized animal, even though they fall in the 2000-2600fps range. The rounds were mainly designed to penetrate armored targets that could be fired from small SMG's and pistols, usually with high capacity magazines at a high rate of fire to make up for the lack of power.

Also no rifle or handgun has 'stopping power' until you get into anti material calibers, IMO.

[robert1811]

Hey JDX in regard to a rifle round penetrating straight through the target and doing immense damage.

I thought the object of hydro static shock (this was the correct term to "damage done" I was looking for) was to dump as much of the bullets energy into the intended target so it all implodes in the target.

Or is this rule of thumb strictly for convential handgun calibers, due to lower velocity? (again I know the target plays a HUGE HUGE factor here)

Oh and thanks for explaining that higher velocities is what creates this effect. I thought it was a higher ft/lbs. Am I understanding this right?


I understand a lot of this has to with what the target is, but as soon I try to label the target in my head, I already start thinking. A 240gr JHP 44 mag moving at 1200 ft/sec and has 767 ft/lbs of energy VS. a 357 mag (buff bore) JHC 125gr bullet moving at 1700ft/sec with 802 ft/lbs of energy, (the 44) may be the better choice when say hunting an ELK because of the 44 mags ability to penetrate due to sectional density.

[robert1811]

IMO there is such a thing a stopping power, notice I didnt say knockdown power. Im simply relating the effect of hydro static shock, which can vaporize soft meaty things in the body without touching them, force whatever your shooting to stop moving. IMO this would cause a one shot stop. How often is debateable, but I dont think there is any mistaking my claim.

[Brian Pfleuger]

I don't make any differentiation between "knock-down power" and "stopping power". Neither exists in any particular definable condition. No firearm that is portable by a human is capable of literally knocking down a man sized (weight) target. It might fall down, it might jump and lose it's balance as a reaction but there is not, can not be, enough force to "knock" it down.

Hydro-static shock is not "knock down power". It is a shockwave that passes through the in-compressible fluids in the body and disrupts/damages the NERVES, mainly, in the various tissues. Any remote damage (ruptures) in the tissue is a result of pressure waves in an closed space (a "bag of water", essentially). For instance, I have seen a deer's heart torn open even though the bullet remained intact, wasn't within several inches of the heart and there was no wound channel (such as from bone) leading to the heart. This is from the pressure wave. It's the same effect that blows a milk jug to bits even though the bullet only hits a tiny spot.

While disrupting the nerves or rupturing the heart may very well cause the target to drop on the spot, it is not the same as the force of the bullet directly "knocking down" the target.

Handguns, certainly those typically carried for SD can not reach the velocities required for hydro-static shock, with a very few exceptions such as the FN5.7.

[robert1811]

^ no kidding...... I understand what hydro static shock is and can do. Notice how i said it isn't "knockdown power". This term would imply that the shooter would also be "knocked down" upon firing the weapon due to equal and oppossite force/reaction (newtons 3rd law).

However, incapacitating a targets CNS will lead to them dropping dead on the ground. Hydrostatic shock can do this. This would imply stopping power, not necessarily knock down power which is why I didnt term it that. Again how often this will happen and what "magic bullet" can make this happen is debatable.

[JD0x0]

Robert, yes the idea is to dump as much energy into the target as possible, but there's a balance. Shed that energy too fast and you risk not wounding deep enough or not getting through bones that you need to penetrate through. I am okay with not dumping 100% of the energy if it means creating an exit wound. Again, it's about a balance, you obviously don't want to just pencil through with a FMJ, but with a good soft point, you could achieve impressive expansion which dumps a majority of energy in the target and still guarantees or offers an extremely high probability of an exit wound. I find that exit wounds tend to be a little more 'discouraging' to threats, and it can help you track your target.

Extremely light varmint rounds which dump their energy as quickly as possible could cause shallow 'explosions' which just blows a shallow chunk of flesh out, where the entrance wound is. Or the bullet could just hit a shallow bone and disintegrate, barely doing damage.
At the same time, if you go with something too heavily constructed for your purposes, you risk "wasting" energy because the bullet penetrated through and through before it had a chance to dump a large portion of it's energy, which is now going to go somewhere behind the target.

[robert1811]

I appreciate the explanation, it really put things into perspective for me. Kudos.

[jnichols2]

I don't know if I'm smarter than you are (probably I'm not), but I do know a few things that apparently, you do not.

ALL rifle bullets tumble. Its because of their shape. The bullet base is heavier than the nose, so after a certain amount of penetration, the bullets swaps ends. The .223/5.56mm round got a huge reputation for this, only because of its small bullet size, combined with the use of a FMJ bullet.

Traditionally, .22 caliber centerfire rifles were always regarded as pest & varmint calibers. The were always loaded with bullets designed to expand as violently as possible (because a bullet holding together for penetration is actually counterproductive when your target is a small animal).

By the early 20th century, the majority of the world's militaries were using approximately .30 caliber rounds (or something between .26 and .32 calibers). These bullets DO tumble after impact. However, most of them do not tumble until after over a foot of penetration of soft tissue. This being the case, the point were a larger bullet tumbles is often after it has exited a person.

This was well known, but not anything of any real importance (or use) until we changed to the very small caliber bullet of the .223. Combining a very small bullet with the military full metal jacket design showed that it begins its tumble after only a few inches of penetration. This does result in larger wounds than if the bullet did not tumble, and was beaten like a cheap drum as justification for using the small bullet (small compared to previous standards).

Oh, and by the way, "truly horrible wounds" are those inflicted on myself, or my friends, only. Wounds inflicted on people I meant to shoot are not horrible, they are efficient.

Very enlightening stuff, particularly the part in boldface.

[lcpiper]

I suppose if one does the math and follows the physics it leads them down a path to the best choice available to the shooter for his intended purpose.

I need a defense round, so the target is a man therefore I need X Energy.
X Energy given different calibers provide a range of choices which can be effected by barrel length, even the weapon type/action, etc.
This leads me to a range of choices for my purchase.
But I need to again consider the physics involved, less recoil means quicker follow-on shots and sometimes greater magazine capacity, barrel length effects the sight radius and accuracy.
Weight plays an important factor here too.
Barrel length and magazine capacity swing back into play when it comes to concealability.
And lastly you get down to preferences, the feel of the grips, etc.

Or just buy the nextest newest neatest everyone's gota get it bullet launcher you can afford and roll with it


And don't forget, "If it was good enough for John Wayne ..."

[RBid]

I would love to see any non-pro shooter get into rapid fire with a .44 Mag. That would be a popcorn worthy YouTube video.

[Hunter Customs]

For self defense at normal self defense distance I put more emphasis on power factor.

Lets take two of the rounds you quoted, the 50gr 223 moving at 3000fps makes a power factor of 150, the 270gr 44 moving at 1450fps makes a power factor of 391.5.

I would easily choose the 44 at handgun distances.

Best Regards
Bob Hunter
www.huntercustoms.com

[Frank Ettin]

Originally Posted by Brian Pfleuger

...Hydro-static shock is not "knock down power". It is a shockwave that passes through the in-compressible fluids in the body and disrupts/damages the NERVES, mainly, in the various tissues. Any remote damage (ruptures) in the tissue is a result of pressure waves in an closed space (a "bag of water", essentially). For instance, I have seen a deer's heart torn open even though the bullet remained intact, wasn't within several inches of the heart and there was no wound channel (such as from bone) leading to the heart. This is from the pressure wave. It's the same effect that blows a milk jug to bits even though the bullet only hits a tiny spot.

While disrupting the nerves or rupturing the heart may very well cause the target to drop on the spot, it is not the same as the force of the bullet directly "knocking down" the target.

Handguns, certainly those typically carried for SD can not reach the velocities required for hydro-static shock, ...

Correct. In general, velocity must be in excess of 2,000 fps for hydrostatic shock to be a factor.

At the velocity of most self defense handgun cartridges, hydrostatic shock is too negligible.

Originally Posted by robert1811

...However, incapacitating a targets CNS will lead to them dropping dead on the ground. Hydrostatic shock can do this...

No it can not -- at least unless one is using a cartridge firing a bullet at a velocity considerably in excess of the velocity of most self defense handgun cartridges.

Let's consider how shooting someone will actually cause him to stop what he's doing.

1. The goal is to stop the assailant.
   
   
2. There are four ways in which shooting someone stops him:
   
   
   1. psychological -- "I'm shot, it hurts, I don't want to get shot any more."
      
      
   2. massive blood loss depriving the muscles and brain of oxygen and thus significantly impairing their ability to function
      
      
   3. breaking major skeletal support structures
      
      
   4. damaging the central nervous system.
   
   Depending on someone just giving up because he's been shot is iffy. Probably most fights are stopped that way, but some aren't; and there are no guarantees.
   
   Breaking major skeletal structures can quickly impair mobility. But if the assailant has a gun, he can still shoot. And it will take a reasonably powerful round to reliably penetrate and break a large bone, like the pelvis.
   
   Hits to the central nervous system are sure and quick, but the CNS presents a small and uncertain target. And sometimes significant penetration will be needed to reach it.
   
   The most common and sure physiological way in which shooting someone stops him is blood loss -- depriving the brain and muscles of oxygen and nutrients, thus impairing the ability of the brain and muscles to function. Blood loss is facilitated by (1) large holes causing tissue damage; (2) getting the holes in the right places to damage major blood vessels or blood bearing organs; and (3) adequate penetration to get those holes into the blood vessels and organs which are fairly deep in the body. The problem is that blood loss takes time. People have continued to fight effectively when gravely, even mortally, wounded. So things that can speed up blood loss, more holes, bigger holes, better placed holes, etc., help.
   
   So as a rule of thumb --
   
   
   • More holes are better than fewer holes.
     
     
   • Larger holes are better than smaller holes.
     
     
   • Holes in the right places are better than holes in the wrong places.
     
     
   • Holes that are deep enough are better than holes that aren't.
     
     
   • There are no magic bullets.
   
   
3. With regard to the issue of psychological stops see
   
   
   • this study by Greg Ellifritz.
     
     As Ellifritz note in his discussion of his "failure to incapacitate" data (emphasis added):

     Originally Posted by Greg Ellifritz

     
     ...Take a look at two numbers: the percentage of people who did not stop (no matter how many rounds were fired into them) and the one-shot-stop percentage. The lower caliber rounds (.22, .25, .32) had a failure rate that was roughly double that of the higher caliber rounds. The one-shot-stop percentage (where I considered all hits, anywhere on the body) trended generally higher as the round gets more powerful. This tells us a couple of things...
     
     In a certain (fairly high) percentage of shootings, people stop their aggressive actions after being hit with one round regardless of caliber or shot placement. These people are likely NOT physically incapacitated by the bullet. They just don't want to be shot anymore and give up! Call it a psychological stop if you will. Any bullet or caliber combination will likely yield similar results in those cases. And fortunately for us, there are a lot of these "psychological stops" occurring. The problem we have is when we don't get a psychological stop. If our attacker fights through the pain and continues to victimize us, we might want a round that causes the most damage possible. In essence, we are relying on a "physical stop" rather than a "psychological" one. In order to physically force someone to stop their violent actions we need to either hit him in the Central Nervous System (brain or upper spine) or cause enough bleeding that he becomes unconscious. The more powerful rounds look to be better at doing this....

   • Also see the FBI paper entitled "Handgun Wounding Factors and Effectiveness", by Urey W. Patrick. Agent Patrick, for example, notes on page 8:

     ...Psychological factors are probably the most important relative to achieving rapid incapacitation from a gunshot wound to the torso. Awareness of the injury..., fear of injury, fear of death, blood or pain; intimidation by the weapon or the act of being shot; or the simple desire to quit can all lead to rapid incapacitation even from minor wounds. However, psychological factors are also the primary cause of incapacitation failures.
     
     The individual may be unaware of the wound and thus have no stimuli to force a reaction. Strong will, survival instinct, or sheer emotion such as rage or hate can keep a grievously wounded individual fighting....

   
   
4. And for some more insight into wound physiology and "stopping power":
   
   
   • Dr. V. J. M. DiMaio (DiMaio, V. J. M., M. D., Gunshot Wounds, Elsevier Science Publishing Company, 1987, pg. 42, as quoted in In Defense of Self and Others..., Patrick, Urey W. and Hall, John C., Carolina Academic Press, 2010, pg. 83):

     In the case of low velocity missles, e. g., pistol bullets, the bullet produces a direct path of destruction with very little lateral extension within the surrounding tissue. Only a small temporary cavity is produced. To cause significant injuries to a structure, a pistol bullet must strike that structure directly. The amount of kinetic energy lost in the tissue by a pistol bullet is insufficient to cause the remote injuries produced by a high-velocity rifle bullet.

   • And further in In Defense of Self and Others... (pp. 83-84, emphasis in original):

     The tissue disruption caused by a handgun bullet is limited to two mechanisms. The first or crush mechanism is the hole that the bullet makes passing through the tissue. The second or stretch mechanism is the temporary wound cavity formed by the tissue being driven outward in a radial direction away from the path of the bullet. Of the two, the crush mechanism is the only handgun wounding mechanism that damages tissue. To cause significant injuries to a structure within the body using a handgun, the bullet must penetrate the structure.

   • And further in In Defense of Self and Others... (pp. 95-96, emphasis in original):

     Kinetic energy does not wound. Temporary cavity does not wound. The much-discussed "shock" of bullet impact is a fable....The critical element in wounding effectiveness is penetration. The bullet must pass through the large blood-bearing organs and be of sufficient diameter to promote rapid bleeding....Given durable and reliable penetration, the only way to increase bullet effectiveness is to increase the severity of the wound by increasing the size of the hole made by the bullet....

   
   
5. Urey Patrick was in the FBI for some 24 years, 12 of which were in the firearms training unit where he rose to the position of Assistant Unit Chief. John Hall is an attorney who spent 32 years in the FBI, including serving as a firearms instructor and a SWAT team member.
   
   
6. And sometimes a .357 Magnum doesn't work all that well. LAPD Officer Stacy Lim who was shot in the chest with a .357 Magnum and still ran down her attacker, returned fire, killed him, survived, and ultimately was able to return to duty. She was off duty and heading home after a softball game and a brief stop at the station to check her work assignment. According to the article I linked to:

   ... The bullet ravaged her upper body when it nicked the lower portion of her heart, damaged her liver, destroyed her spleen, and exited through the center of her back, still with enough energy to penetrate her vehicle door, where it was later found....

[Koda94]

What is the determining factor?

IMO Marksmanship and penetration. I suppose under stress if your marksmanship is reduced then more and bigger bullets would be ideal.

Didn't the FBI determine what the ideal penetration distance was?

[KyJim]

Specifically regarding the .223/5.56mm, at speeds above about 2600 to 2700 fps, the bullet will enter a soft target (body) and begin to tumble severalinto the target and begin to fragment. While this is not good for most handgun rounds, the .223/5.56 fragments are traveling fast enough that they penetrate deeply enough to reach vital organs. Thus, you have a very devastating wound. That's one reason why the carbines (16 inch barrels) begin to lose effectiveness at distances of more than 100 yards (some say even beyond 50 yards).

[robert1811]

Koda yes the FBI says its a minimum of 12 inches.

THANK YOU GUYS! Excellent insight. And yes I have a lot of those documents in PDF format on my laptop. Also ive seen plenty of surgeon videos showing bullet wounds explaining what will happen to victims for the purposes of teaching med students.

I find it very interesting.

[johnwilliamson062]

I always just go with LOTS of bullets. It doesn't really matter which kind. LOTS of 22lr works well enough.