Do 5.56 fmj often break up when they hit flesh or water?

When they hit, rarely, as they penetrate, I'd say it depends on the FMJ and the velocity.

I do recall a bit of talk about the performance of the standard 62gr stuff overseas. Back when they went to the M4 carbine and other short barrels variants, the talk was that long range performance was disappointing.

They said that the FMJ usually broke apart at the cannelure as it tumbled through flesh, creating a second wound channel and so doing more damage. Some said it was designed to do this. Others just said it frequently happened.

They also said that when fired from the short barrel guns when the bullets got out to 200 or 250m (depending on who was telling the story) the velocity had dropped "too low" and they no longer broke apart.

like the line in one of my fav old movies...

"Can't say its true, and won't say its not, but, there's been talk!"
 
Look up ballistic gel tests. Folks who do war test such things.

I think its a "sometimes, maybe" Its been a while since I looked. As I recall,the 75/77 gr bullets might tend to bend,yaw and break.

Search "LuckyGunner" He has done and published a lot of gel tests.

PO Ackley "Handbook fir shooters" ....I forget vol 1 or 2? Had info on military gunshot wound trauma. Thats all been tested, goats,hogs etc.

Pretty much there are so many variables its tough to predict.
 
From what i hsve seen, they tend to yaw or tumble. The bullet bay flatten on its long axis and squish lead out the back. But break up or fragment ? Cant say as i have seen that.
 
Rarely. And the surgeon who spoke yesterday (bank shooting) regarding all the devastating damage to bone and soft tissue from the AR is both full of stuff and an obvious anti "black gunner". He said no handgun compared in the damaging effects. Yes it happens but not the norm.
 
Thanks for the responses.

Thanks Double naught spy. The video makes it definitive. Regular full metal jacket 5.56 ammo usually breaks up when passing through soft tissue.
 
Kind of surprised by some of these answers. My understanding is that 5.56 not only yaws when it hits, but also fragments ... which is why it tends to cause a lot damage than a much larger pistol round (230 gr. .45 for example). However, to do this it has to hit with a certain velocity. Which is why short barreled rifles start losing some of their effectiveness once you get out to 150-200 yards, and once you get out to 400+ yards the terminal performance of all AR's regardless of barrel length becomes somewhat compromised. And yes 77 gr. OTM ammo is generally considered superior to 55/62gr. as far as terminal performance is concerned.

And I do agree with another poster that the notion that a 5.56 round is somehow super deadly as opposed to any other bullet is wildly exaggerated. Yes, compared to a pistol round, which is generally traveling a 1/2 the speed, it does a lot more damage. Compared to a lot of rifle rounds, not so much. Of course, most ER doctors are probably never going to see someone who's been shot with a 50 BMG, .458 Socom or even a 300 BO round in their lifetime.
 
Due to the difficulty in making things exactly perfect, everything that is spun is going to have a degree of yaw.

And every projectile that ls longer than it is wide is going to tip, and eventually tumble passing through some flesh or some other similar substance.

Where the variables come in are how much, and how soon (measured by distance traveled in the target media.

The regular GI .30 cal bullet also tumbles. Because of its mass and speed it usually doesn't tumble until after it passes through a human size body. SO nobody sees that, and assumes it doesn't do what the 5.56 slugs do. IT does, (more or less) but not on a scale where it is ordinarily seen, which is what the 5.56 slugs do.

Very few ER docs have much experience with rifle wounds. Particularly the more powerful rounds. What they see is handgun wounds, mostly, .223 and 7.62x39 sometimes, which do "tremendous" damage, compared to what they usually see. Someone who has served as a medic/dr in an active war zone has a different point of view and probably isn't writing opinion pieces about how horrific 5.56mm wounds are. Interestingly, I don't recall any of those ER folks writing how horrific 5.56 wounds are comparing them to 12ga slugs...:rolleyes:
 
Or shoulder shoot a pronghorn with a 7mm Rem Mag loaded with 70 gr of surplus (old school) H-4831 behind a 160 gr Sierra Boat Tail . Messy.

A Doctor probably would never see it. The Coroner would. Exit would pass a small cantaloupe, lots of soupy crepitus. My first big game shot.

Later I built my 257.

Not all DR's are prepared for 2400 to 3200 fps trauma.
 
SS109 breakup inside human leg from ND.
https://www.researchgate.net/figure...th-a-556-mm-bullet-following-a_fig4_295542470

From AR15's Ammo Oracle: https://www.ar15.com/forums/ar-15/Fragmentation_and_the_5_56_/16-619367/
Unlike most FMJ rounds, M193 and M855's primary wounding mechanism is fragmentation. This is a good thing because without fragmentation these rounds otherwise would act like a ice pick and cause very little damage because of their small size. At the proper velocity, both M855 and M193 strike flesh and immediately begin to yaw (tumble)...

If the rounds are moving fast enough when they yaw to about 90 degrees of their original trajectory the stress on the bullet from traveling sideways through a dense medium (tissue) will overcome the structural integrity of the bullet and it will start to break up.

If the velocity is high enough this breaking up is pretty dramatic and causes equally dramatic wounds. This is because the fragments travel rapidly through the temporarily crushed tissue and tear it.
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Some of Fackler's thoughts...
https://pubmed.ncbi.nlm.nih.gov/6694223/

I mentioned the need for sufficient velocity. Apparently, that meant an impact velocity of at least 2700 fps for M193 55 gr. ball ammo for reliable fragmentation.
 
Interesting tidbit, there are reports from the Vietnam days (so that would be the M193 55gr round) that sometimes, (not always but often enough to be remarked on) that the 5.56 was "curiously less effective" at very short range (25m and under).

Bearing in mind that combat reports must always be taken with a grain of salt, as there is never any way of knowing if something "failed" because it didn't work, or if the GI simply didn't hit the enemy in a vital spot, and all such things (good and bad) get embellished and retold over and over, and as Tolkien remarked about his stories, "the tale grew in the telling..."

True or not, there was a belief that a really close range (and so highest velocity) SOME of the time the 5.56 didn't do the tumble and "massive wound" thing but did the icepick 'punch a small hole through" thing.
 
I think the early m16 barrels had slower twist rate (1:12?), which made the bullet more prompt to tumble. Now I heard more complaints on 5.56 bullets going through and through, without sufficiently disabling the enemy.

-TL

Sent from my SM-N960U using Tapatalk
 
variables

believe it is a matter of record that some 5.56 FMJ projectiles will fragment some of the time. I would think that there are many variables effecting whether or not that happens. Velocity at impact, such effected by range and barrel length. Too, barrel twist rate as well. Early 20" slow twist M16 barrels had slow twist rates which supposedly contributed to projectile yaw, subsequent fragmentation and effective wounding. As barrels shortened, twist rates increased , projectiles grew heavier and velocities dropped, the 5.56 projectile reportedly became more stable, and reports began about the 5.56's lack of wounding effect.
 
I think the early m16 barrels had slower twist rate (1:12?), which made the bullet more prompt to tumble
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Early 20" slow twist M16 barrels had slow twist rates which supposedly contributed to projectile yaw, subsequent fragmentation and effective wounding.
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I have a theory, about the yaw, and tumble and, it has nothing to do with the twist rate.

First point, the "slow" twist of the early ARs. It wasn't slow at the time it was the regular twist rate for most .22CF cartridges. .22 cal twist rates were 1-12" or 1-14". The AR-15 had a 1-12" twist and so did the GI M16 barrels. That twist rate gave good accuracy shooting bullets of 55gr and under. They used the same twist rate as commercial sporting rifles. For accuracy.

Experts who have studied such things will tell you ALL bullets will yaw and eventually tumble passing through flesh. Even all the WWII battle rifle rounds with "large" (compared to .22 cal) bullets do this. This is known, and has been for a long time. Just not by most people. Most people never see it happen, because it takes something on the order of 2 feet of passage through flesh for a .30-06 to reach its tipping point, and the overwhelming majority of the time, the bullet has exited the body before that. SO since "nobody" saw it, most people assumed they didn't tumble. But, they do, they just don't do so inside a person, usually.

The smaller lighter and faster .22cf bullets tip "sooner" and often while still inside a human body. But, other than experts in the field, no one realized that, either, because until a .22cal military rifle was being considered (the AR) nobody was shooting people with .22 CF or varmints with FMJ ammo.

Remember that until after we adopted the 5.56mm, about nobody considered any of the .224 centerfires as anything other than varmint rounds. Varmint hunters never saw "horrific wounds" from an FMJ tumbling, they didn't use FMJ (and were shooting varmints, much smaller than humans). They saw "horrific wounds" from thin jacketed bullets at high speed "blowing up" on impact. Which is what they wanted.

SO, along comes the military, who must use FMJ ("solids") and because the bullets DO hold together enough so that the yaw and tumble (and breaking up when sideways) can be seen by the users and the doctors, people think its a new thing, something the round was "designed to do"

I don't think it was "designed" to do it, any more than any bullet is designed to do it. I think that prior to the use of the 556 in combat no one noticed (again outside of experts) that it happened and that "it was designed to do that" is just one more piece of the inaccurate BS told about the M16 rifle & round to give skeptical troops more confidence in the new rifles that looked like a toy and shot a tiny bullet that wasn't even legal for deer in most states.

I got told a lot of those things by various NCOs when I was a private.

the twist rate of the M16 was the same twist rate that was routinely zapping varmints at range, and shooting groups small enough to hold benchrest titles for many years.

Stoner said more than once that he designed the AR15 to be lighter and more accurate than the AK. I've never seen anything where he said he designed the rifle, twist rate, or the cartridge to make the bullet tumble on/after impact. IF you have, please share!!

Simply put, all bullets get "knocked off plumb" when they hit something. They are going to tip, and eventually tumble. That's what bullets do. How soon, and how much, and if they do it inside flesh depends on lots of variables. I think anyone claiming the 556 was specifically and intentionally designed to do it, is passing on misinformation, most likely without realizing they are doing it.
 
SO, along comes the military, who must use FMJ ("solids") and because the bullets DO hold together enough so that the yaw and tumble (and breaking up when sideways) can be seen by the users and the doctors, people think its a new thing, something the round was "designed to do"

I don't think it was "designed" to do it, any more than any bullet is designed to do it.
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No, it was not designed to come apart. Other FMJ have been known to do this as well. If it was 'designed' to come apart while tumbling, I would love to see the spec sheet with the design parameters that make this happen.

I think anyone claiming the 556 was specifically and intentionally designed to do it, is passing on misinformation, most likely without realizing they are doing it.
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And a lot of people doing it either learned it in the military or learned it from someone who was who learned it in the military...which goes along well with similar things taught to recruits like that the bullet was made to wound and not kill or that .50 BMG was illegal for use against people and could only be used for materials. Recruits are/were fed a lot of informational garbage to make them feel confident about their training.
 
slow twist

Rereading my post I can see where I could have worded things a bit more clearly. I did not intend to imply that the early M16 was twisted 1-12" to INTENTIONALLY impart earlier yawing. And yes, 1-12/1-14" was indeed standard at the time, I've got bolt varmint rifles so rifled. But the result of the slow (by comparison to current faster twists) was tumbling, fragmentation and reportedly at least, wounding effect. As twist rates tightened to stabilize longer projectiles, and correspondingly, velocities dropped with shorter barrels, those properties were reduced.
 
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