Tumbling bullets in the AR-15

[cdoc42]

Following the shooting in Virginia, before it was clear what weapon was used, another fellow surmised it was an AR15 and related the devastating wound was probably due to the bullet "tumbling."

It is my impression that "tumbling" dates back to the Vietnam era and the introduction of the AR15 with a 1:14 twist that stabilized a 55gr bullet until it hit the target, then tumbled due to yaw and instability. At greater distances the accuracy was poor and the twist was changed to 1:12. I have a 1:7 twist and I don't see any keyholes at any distance. So my position was if the shooter used a modern AR15, tumbling was not part of the equation.

But the other fellow says he has both a 1:7 and 1:8 twist and both rifles tumble his bullets of ALL weights.

What do you other shooters think?

[ed308]

None of my ARs tumble bullets. The only firearm I've owned that tumble bullets is a Sig P238. A good cleaning of the barrels seems to fix it.

[Rob228]

I would guess whoever reported the tumbling was looking at very old information. From what I have read there were hundreds of fragments that the doctors had to remove, which leads me to believe the guy was using varmint bullets.

[rickyrick]

ARs and other guns that shoot .223/5.56 do a lot t of damage due to the high velocity of the bullet. You can get some pretty incredible terminal effects with light bullets.

[cdoc42]

I think it has been reported he used a "SKS" which I believe is 7.62 NATO or .308, which makes more sense given the damage that was done. A FMJ 5.56 would more likely poke a hole in the hip bone, slow down and the damage would be a result of whatever hydrostatic effect was left. A .30 caliber expanding bullet would more likely break the hip, expand and cause a lot of internal organ and blood vessel damage.


But that aside, the discussion relates to whether or not today's AR15 bullets "tumble" as they did in the 60's.

[CarJunkieLS1]

Originally Posted by cdoc42

I think it has been reported he used a "SKS" which I believe is 7.62 NATO or .308, which makes more sense given the damage that was done. A FMJ 5.56 would more likely poke a hole in the hip bone, slow down and the damage would be a result of whatever hydrostatic effect was left. A .30 caliber expanding bullet would more likely break the hip, expand and cause a lot of internal organ and blood vessel damage.


But that aside, the discussion relates to whether or not today's AR15 bullets "tumble" as they did in the 60's.

That is INCORRECT. The SKS fires a 7.62x39 cartridge. It is NOT a .308 or a NATO cartridge. I can not speak to the bullet that was used but I know for a fact the most common ammo is a 123 FMJ and I have seen first hand the type of damage that the round can do. Based on the assumption he used a FMJ the bullet struck a bone the damage was from bone fragments not from bullet expansion.

Many years ago 2 Police Officers were gunned down in my hometown. A SKS firing FMJ ammo penetrated the cars hood, firewall, dash, body armor car seats, and exited the trunk. Those rounds do not expand at all but they are extremely lethal.

[xandi]

Yeah the m855/ss109 round will tumble and break at the cannelure if its going fast enough

[FrankenMauser]

Bad crowns and/or crap ammo will make more bullets tumble than any amount of twist rate, velocity, or bullet weight discussion.

Many years ago 2 Police Officers were gunned down in my hometown. A SKS firing FMJ ammo penetrated the cars hood, firewall, dash, body armor car seats, and exited the trunk. Those rounds do not expand at all but they are extremely lethal.

Some FMJs expand.
Some don't.
Some penetrate well.
Some don't.

Many of the FMJs being stuffed into modern, commercial 7.62x39mm cases tend to fold over, tumble and separate (core and jacket), or fragment.

Jackets can be steel, copper, and/or various other allows.
Jackets can be thick or thin.
Cores can be hard or soft.
Penetrators may or may not be present in some old import ammo.

It isn't prudent to judge an entire array of cartridge loadings and hundreds of different FMJ bullets, based on the performance of a single example (with no specific details, at that).

I've fired a lot of FMJs, from .22 WMR to .30-06 to .450 Nitro. The best penetration I've ever seen was a tie between a soft-point hunting bullet (.375 H&H) and a hollow-point hunting bullet (.44 Mag).

Just because a bullet is a 'full metal jacket' doesn't mean that it's actually a tough bullet, or a good penetrator.

[CarJunkieLS1]

Franken I understand what you are saying but the very common 123 FMJ found in Russian X39 ammo just doesn't expand. Its a bimetal jacket that a magnet sticks too with a steel core. I've fired and seen fired enough of them into anything you can think of to know that they just don't expand, they do however deform, depending on what they are shot at.

I can say 100% that the instance I mentioned that a SKS and 123 fmj russian ammo was used and based upon the damage to the cars and wounds to the officers there's just ZERO evidence of bullet expansion.

[Chainsaw.]

The vietnam era 556 had massive terminal effect due mostly due to velocity. IIRC the original loading out of a 20" barrel resulted in butt nekkid speeds somewhere in the range of 3600 fps. This combined with the twist rate apparently made for some rather grievous wounds for suck a small bullet. One report was of a short fire fight where several VC were killed, one what shot in the ankle, apparently the hydrostatic shock was so great that the veins in the leg blew out which lead to the person bleeding out in short order. Now this of course is all hearsay and from my crappy memory so take it for what its worth. But yeah, it used to do nasty things. Todays guns/ammo I dont think are quite so devastating given some of the coroner's reports. Non the less, I dont want to be on a two way range with one.

[FrankenMauser]

Franken I understand what you are saying but the very common 123 FMJ found in Russian X39 ammo just doesn't expand. Its a bimetal jacket that a magnet sticks too with a steel core. I've fired and seen fired enough of them into anything you can think of to know that they just don't expand, they do however deform, depending on what they are shot at.

I can say 100% that the instance I mentioned that a SKS and 123 fmj russian ammo was used and based upon the damage to the cars and wounds to the officers there's just ZERO evidence of bullet expansion.

Good.

How can you apply those questionable examples to .223/5.56 bullets tumbling?

[Mobuck]

Intentional bullet tumbling is a factor of bullet design. Bullet tumbling as a consequence of firearm design is poor engineering.

[stagpanther]

Is the OP talking about in-flight instability--or the propensity for the bullet to yaw upon impact with flesh?

[Bartholomew Roberts]

cdoc42, you are confusing two different concepts - what happens to a bullet in flight and what happens to the bullet when it hits the targets. Bullets are spin-stabilized in air. If a round is actually tumbling in the air to the extent it keyholes a paper target, then the round doesn't have a fast enough twist for its length and your accuracy will be very poor.

The twist rate has nothing to do with what happens when the bullet hits the target. I am not aware of any rifle in the world with a fast enough twist rate to spin stabilize a bullet in tissue - which is mostly liquid. All spitzer bullets will eventually tumble because of the way their shape decelerates when it hits a target. A heavier bullet will usually take longer to decelerate/tumble and may well exit the target before that happens. The angle of the nose of the bullet when it hits the target also has an impact on this.

Light spitzer bullets will decelerate or tumble faster - and if they are moving fast enough, they may even break up under the stress.

Regardless of whether you use a 1:14, 1:12, 1:9, 1:8, or 1:7 twist, 55gr M193 will tumble when it hits ballistic gel. Where it tumbles and the result you get when it does, depends on several factors but twist rate isn't one of them.

Also, the twist rate on the M16 was changed from 1:14 to 1:12 because during artic tests, 1:14 provided borderline stability in the colder, denser air.

[CarJunkieLS1]

Originally Posted by FrankenMauser

Good.

How can you apply those questionable examples to .223/5.56 bullets tumbling?

I can't speak to 5.56 bullets tumbling I made no reference to such either. I made reference to the devastating wound characteristics in the shooting victims in the OP. He stated it was surmised that it was an AR-15 and the bullets tumbled that caused those wounds. I said it was wrong and that a 7.62x39 was used and I made an assumption that FMJ's were used.

[mehavey]

Let's take a look at some facts:
http://www.ciar.org/ttk/mbt/papers/m...ckler.unk.html

(...including Figs. 3 & 7)

[44 AMP]

Every bullet that is longer than it is wide has the potential to yaw, and then tumble while travelling through flesh (or gel). EVERY bullet.

Many cartridges do not have the energy to drive the bullet far enough through flesh for the tumbling to occur. Many others have the energy to drive the bullet completely through before tumbling occurs.

The 5.56mm got its reputation because of two things. First, it was the first time (in history) we used a bullet small enough and fast enough to often show the tumbling effect within a body, and second, it was played up, primarily as a way to convince troops that the "little .22 caliber" could be effective.

I took a look at the linked report (Fackler) and one thing stood out to me, the wound channels of the 5.56mm and 7.62x51NATO (US). (and btw I hate he put everything in the metric system, I think in inches )

15cm tissue (gel) depth call it 6 inches.
The wound cavity of the 5.56mm is at about at its maximum.

The 7.62NATO bullet cavity reaches its max about 30cm of penetration.

Think about that for a moment.

[bfoosh006]

Stagpanther ... has it right... Yaw is the correct term in context to 5.56. The greater the impact angle ( yaw ) the "earlier" the M193 bullet will fragment from the loosely used term tumbling>

Quote ...
"The bullets go through this yaw process on the way to becoming stable, and can yaw by as much as 4 degrees at short distances. You can see in the graph above that the bullet becomes very stable from about 100-400 meters, but the greatest variability - unfortunately - is within CQB range. The angle of attack has a profound impact on how a bullet behaves when striking tissue. Consider the two bullets in the picture below::







And not all 7.62x39 bullets behave the same.. the Yugo bullet will tumble quite differently then the average Com Bloc bullet.

[cdoc42]

Wow! What a load of valuable information here! You can never get old enough to know everything.

Re: Bartholomew Roberts post, when I re-read my original post, I think I understood that twist stabilized a bullet in flight, not after it impacted the target. Key-holes would be different because it reveals instability at the point of impact because you can see that effect. On the other hand, the other fellow with whom I had the conversation that led to this post told me that all of his bullets tumble, regardless of twist. From the posts that followed herein, I wonder how he could determine that without shooting into ballistic gelatin or other experimental media.

[Slamfire]

I recommend reading "The Gun" by Chivers. https://www.amazon.com/Gun-C-J-Chivers/dp/0743271734 You can get a used version for $6.00! Chivers did excellent research on the development of the M16. He examines the massive propaganda campaign to sell the rifle and replace the M14. The rifle and its cartridge were sold based on whole bunch of lies and pseudo science. Gun writers and Gun Magazines were highly complicit, if not central to this. One of the lies was the "devastating effect" of the tumbling of the bullet. I remember a relative who came out of boot camp, around 1968, and he was repeating that nonsense about the horrible wounding effect of the M16 due to the high velocity and tumbling of the bullet. M16 advocates were claiming decapitations, arms and legs blown off, and because this was repeated endlessly in the Gun press, this nonsense is still vaguely remembered, after sixty years.

Well, any long bullet, if you can get it to tumble, will cause nasty wounds. The British had been doing it with their 303 rounds since WW1, nothing new there. However, getting the thing to tumble, now that is the trick, the bullet does not dance predictably. When the 5.56 does not tumble, all you have left is a poodle round that makes a small hole.

[hdwhit]

cdoc42 wrote:
But the other fellow says he has both a 1:7 and 1:8 twist and both rifles tumble his bullets of ALL weights.

Lots of unknowns here.

Does this "other fellow" know enough to understand how he would determine whether a bullet was tumbling in flight? I know a lot of people who have more guns than Carter's has little pills that think smokeless propellant explodes when the primer is struck. And I'm pretty sure none of them understand the difference between tumbling in flight as opposed to tumbling within the body of the target.

Also, how does this "other fellow" take care of his guns? If he's feeding them a diet of imported bi-metal projectiles and he shoots a lot, he just might have tumbling bullets because he's worn his barrel out to the point where it is effectively a smoothbore.

[cdoc42]

hdwit, my impression was that he had keyholes, which I interpret as instability in flight. As I said, short of using ballistic gelatin or some similar medium, how can anyone determine their bullet tumbled AFTER it entered the target? Especially, as well pointed out here on these posts, differences in bullet construction determine how they act after entering the target. Even at that, on a practical basis it's difficult for the average shooter to figure it out. I'm shooting a 52gr Sierra Match HP in my .22-250 for ground hogs which is not particularly advised for hunting by Sierra. But I hit one standing hog in the back and the front looked like someone opened him up with a zipper. Another running hog was hit from the side and dropped dead on the spot but the bullet never came out and all I could find was the small entrance wound. Same bullet. Same rifle. Go figure.

[bfoosh006]

cdoc42.... you may have experienced a difference in impact yaw between those two kills... just like the photos show.

And that would be exactly why Sierra doesn't recommend it for hunting... inconsistent bullet performance.


Without trying to sound flippant in any way.... Sierra didn't design that bullet as a hunting bullet...so the design parameters revolved around accuracy, not reliable consistent expansion....

The newer Sierra TMK's were specifically designed to be less "Yaw dependent"... and have a "mechanism" to promote reliable consistent performance. ( The poly tip )


As for testing bullets for whether or not they "tumble" ... you would have to shoot quite a few rounds to be able to tell if they do...

Soggy 24hr soaked newspaper... will show a reasonable "wound channel"... not as good as gel... but...

If the bullet fragged consistently , 9 out of 10 times, then you could maybe trust its performance.

A strictly tumbling bullet would NOT frag... and would be intact, but probably slightly bent... after travelling maybe 18-24".

[Jimro]

This is one of those subjects that keeps coming up. All spitzer style full metal jacket bullets will tumble in tissue. All of them, it isn't unique to the AR-15 or M16.

The only question is how long it will take for that tumbling to begin. For a standard 7.62x51 M80 projectile, that starts around 8 inches. For a standard 5.56x45 projectile (assuming no fragmenting happens) that happens around 3 inches.

The longer and skinnier a spitzer bullet is, the shorter time it takes to disrupt in tissue. The shorter/fatter bullets take a much longer time.

The reason spitzer bullets tumble in tissue is that like all modern projectiles, they are spin stabilized. However unlike their round nosed forefathers, they have the center of gravity moved much more rearward. This means that the tissue medium can "torque" on the nose portion bullet much more effectively than the older round nose bullets which would have almost equal forces acting on the bullet BEHIND the center of gravity.

I hope this explained things succinctly.

Jimro

[stagpanther]

I would add that the bullet's construction charcteristics--and how that's affected by it's velocity--adds a bit to that equation.