Ah! rumors about the early M16's "unstable bullet"

CrazyLarry:

I never claimed that Tom was wrong, nor did my tone ever get hostile as yours has become. I simply stated why I had a hard time believing the claim that you wrote, especially because your post was supposed to help quell a rumor but seemed--to me at least--built upon a rumor itself.

Given what Art Eatman and Al Thompson have written, I'd say Tom's claim is more credible in my eyes. Isn't that the purpose of these threads?

If you are going to post messages and expect everyone to agree with you, or that everyone will completely understand everything you write, I'm afraid you will end up disappointed.

<Art Edit>
 
5.56 bullets can do some crazy things when they hit bone and tissue. I have heard the stories from Viet Nam about someone getting shot somewhere with a M16 and the bullet exiting in a totally different place. I always held these stories with a grain of salt until I deployed to Iraq for the first time.

Here are a couple of instance that I have seem firsthand on 5.56 bullets traveling a erratic path after hitting living tissue. I saw a guy get shot in the foot with a M249 SAW about 5 meters away. The bullet struck the bones in the ankle, turned 90 degrees, went up his lower leg shattering his shine bone, and came out sideways blowing out his knee cap. This was with M855 62 gr. Ball.

I saw a buddy of mine shoot an insurgent about 200 meters away with a M4 through the side. It hit a rib and the bullet exited his lower back, taking a kidney with it. Also with M855 62 gr. Ball.

In almost all the the shooting I have seen with 5.56 the bullet has either tumbled or fragmented if the ranges are 250 meters or less with an M4 or 450 meters or less with a M16A2 or M249. The wounds generally are pretty nasty. Once the bullet starts to tumble or fragment, it usually doesn't follow a straight path.
 
Demon5Romeo:

Now we're talking apples to apples. It's always good to get info from an actual witness.

Sounds like you and your comrades-in-arms are doing good work over in "the world's largest kittybox." Stay safe and don't uncover any "t*rds" under the sand.

Your sig line mentions Saddam's kids. When a guy names his sons Uday and Qusay, I'm afraid to ask what he named his daughter.
 
As I recall from The Black Rifle, Gene Stoner specified 1:14 twist when they scaled down the AR10 to use the 222 Remington Special (early name of .223/5.56) which barely stabilized the bullet. Thus, it would dive and dart once it hit a semi solid medium, like flesh. The military (in its infinite wisdom) wanted cold weather accuracy for arctic conditions so the twist was quickened to 1:12, which brought accuracy up but the lethality down some.
 
http://www.ammo-oracle.com/body.htm#twistduh

Q. If I increase spin or barrel twist, won't that decrease wounding by making a round more stable in tissue?

No.

[...]To describe how stable a given projectile is we use the gyroscopic stability factor (Sg). Generally you want a factor of 1.3 or greater for rifle rounds. 1.5-2.0 is a generally accepted value for 5.56 rounds.

For M193 the following variables apply:

axial moment of inertia (A) = 11.82 gm/mm2
transverse moment of inertia (B) = 77.45 gm/mm2
mass (m) = 3.53 grams
reference diameter (d) = 5.69 mm

Using the gyroscopic stability formula: Sg = A2 p2 / (4 B Ma) and assuming sea level we use an air density of 1.2250 kg/m^3 and discover that this this projectile will need on the order of 236,000 rpm for good stability (Sg > 1.3).

At 3200 fps M193 is typically spun up to more like 256,000 (1:9" twist) to 330,000 rpm (1:7") so that Sg approaches 1.9 or 2.0. 1:12" rifles will spin rounds at around 192,000 rpm and 1:14" rifles around 165,000 rpm. You can see why 1:14" rifles might have had trouble stabilizing M193 rounds.

Clever math types will see that density of the medium traversed (air in this case) has a dramatic effect on the spin required to maintain the Sg (density being in the first term's divisor). This is why cold conditions tend to dip "barely stable" rounds below the stability threshold. Without doing too much calculus it will be seen that an increase of three orders of magnitude (1000) in this variable will be a dramatic one for spin requirements. To balance things spin must be increased to compensate.

Through human flesh (which varies from 980 - 1100 kg/m^3 or about 1000 times the density of air) something on the order of 95,000,000 - 100,000,000 rpm is required to stabilize a projectile at speed. Given these differences it will be seen that the difference between a 1:12 or 1:14" twist when it hits flesh and a projectile launched from a 1:9 or 1:7" weapon is so small as to be beyond measuring. But the game isn't over yet.

[...]

In summary, and to take the most extreme case, a M193 projectile spinning at 350,000 rpm (from a 1:7" rifle) is going to upset in flesh (yaw) exactly as fast as one spinning at 150,000 rpm (from a 1:14" rifle). Claiming that twist rate has any impact on the speed of yaw and therefore terminal performance is just not in line with the laws of physics.
Click to expand...
 
Great, but the Arctic testing still revealed that the higher twist rates didn't stabilize the bullets sufficiently to give reasonable accuracy.

Using your math, the 1:14 twist may well have failed to stabilize the bullet enough to maintain in-line flight. At the distances used in jungle fighting, the bullet may already have begun to yaw/keyhole just as the average engagement range was reached.

I personally witnessed a SOG Team in which a member had taken his XM77, removed the flash supressor, and used a file to notch the crown. After replacing the flash supressor, he test-fired the weapon. It was wildly inaccurate at more than 25 yds. The bullets were key-holing at that distance. His experience had been that even these rounds were unpredictable in bullet path in flesh. More unpredictable than the issue ammo. I wouldn't recommend field-expedient testing of that sort, as it's not onlt your life on the line, but your buddy's as well. You see a lot of crazy crap at times like that.:)
 
Why would it show on paper?

If it took the body (human or other) to start the keyhole process?
If it is yawing and tumbling and shows on paper it surly can't be doing a good job for accurracy.
If you can't hit your target it has to be very depressing if you are being over run.
Sounds like they needed more hand grenades. Talk about fragmentation.

But you still need a good shooting rifle or pistol, if it gets there by chance it is going to take 3 times the ammo needed to get the job done.

HQ
 
Harley,
In shooting ARs & Mini-14s for a few years, I've never seen a 5.56 or a .223 bullet hit a paper target sideways. Admittedly, most of that has been with various commercial loads, but even in four years of qualifying with the original M16 I never saw anything but a perfect hole in the paper out to 100 yards.
I think it's important to understand the difference (and there is one) between the two types of "stabilization" as applied to the 5.56 round.
One refers to keeping it flying straight (in relative terms) in trajectory and following a predictable path/arc.
The other refers to what it does in living tissue.
Some twists and velocities may result in an erratic flight once the bullet gets out to a certain distance.
Bullet spin, velocity, and construction can affect what a bullet does once it encounters living tissue (along with the density & depth of that tissue).
You're absolutely right in saying that yawing in flight is not conducive to accuracy, but the M16 & variants are generally not considered to have an accuracy problem. The "problem" lies in what the bullet does (or does not do) when it arrives, rather than what it does in getting there.
That's what gives rise to the old saying among military gunnies that if you want a target rifle, get a 16, if you want a battle rifle get an AK. :)
Denis
 
for any of the ladies that were offended by my delited reply on this subject I appoligize and will watch it in the future.:o 4 or 5 scotch's and I fell like it's the early 70's again.:eek:
 
Buster51

I was wondering how long that post was going to last. I am glad I got to read it. Refreshing to say the least.:D

At least they did not shut the thread.:cool:

DPris, Thanks for the explanation. My son carried the varient, 3 shot burst when he was in, he liked it.
HQ
 
Bs

A lot of what was told to servicemen about the M16 rifle, and its round was/is BS. When the M16s took their place as general service rifles in Vietnam, many of the troops were (understandably) skeptical. Lots of BS went out, about the "tumbling" bullet, about the "never needs cleaning" rifle, and every possible variation. And then even the BS was misunderstood !

Changes in the ammo specs, misunderstanding of the rifle mechanism, and the situations that only happen in combat all added to the BS, and the myth/legend of the M16 being the "deadliest rifle ever" or the "worst POS we ever had" became part of our culture.

FMJ bullets DO "tumble" after hitting flesh. Bigger bullets do it slower, and penetrate more deeply before turning base first, but they do it. All bullets take random and unpredictable direction changes after hitting bones. Smaller bullets are more extreme in this regard.

These facts were emphasized with the M16 round, to convince the troops that the rounds would work well, even though the were "tiny".

The BS about the M16 rifle/round are now "proven facts" and debated endlessly, with greater or lesser relationship to the real world performance of the gun/ammo system.

The AR design and it's ammo have been tinkered with for over 40 years, and have come a long way, but they will never be all things to all people. Nothing could be, but unreasonable expectations and beliefs still persist.

There is no magic bullet. There is no free lunch. When someone claims otherwise, chances are they are selling something!
 
I was talking to some Australian Training Team Veterans' who said that when they were not terribly pleased to be issued with US M16's (Australia at the time issued the FN-FAL) and that the first thing they did was to dissapear to the range with a large volume of ammo and shoot out the rifling to ensure that the bullet was unstable.

I to have heard tales about the instability of the initial M-16 bullets because of rifling twist rates and note that Gabriel Suarez in'The Tactical Rifle' indicates M193 ammo will yaw to 90 degrees, flatten and fracture at the cannelure if impact velocity is at least 2,700 fps. He quotes US Army Ballistic Lab research for this.

2,700 fps equates to 150 yards in a 20'' bbl or 75 yards in a 16'' bbl.
From 2,500-2,700 there may be a break at the cannelure without fragmentation and Below 2,500 fps he writes, there will not be any break up and the wound will not be dramatic.
 
I was talking to some Australian Training Team Veterans' who said that when they were not terribly pleased to be issued with US M16's (Australia at the time issued the FN-FAL) and that the first thing they did was to dissapear to the range with a large volume of ammo and shoot out the rifling to ensure that the bullet was unstable.
Click to expand...

That seems like a good way to make your sights useless.

I to have heard tales about the instability of the initial M-16 bullets because of rifling twist rates and note that Gabriel Suarez in'The Tactical Rifle' indicates M193 ammo will yaw to 90 degrees, flatten and fracture at the cannelure if impact velocity is at least 2,700 fps. He quotes US Army Ballistic Lab research for this.
Click to expand...

Fragmentation of M193 will occur the same whether fired from a 1:14" barrel or a 1:7" barrel.
 
He's right because if you shoot a different weight Round than designed for the rifling what will happen is the round can yaw off target. This is what happened to my unit in Fort bliss, Texas at a firing range.
 
At what distance did your "yawing" occur? My guess is beyond 100 yards, a mismatched bullet weight & spin rate can result in steady trajectory out to a certain distance, and then you may get an erratic change in bullet flight.
Did you experience it closer?
Denis
 
Bullets are either stabilized in air (or other media) or they are not, period. 55 grain bullets fired out of 1/7" twist barrels are not "overstabilized", they are stabilized. 62 grain M855 ammo is stable in flight from a 20" AR for about 90 - 110 yards under most atmospheric conditions, after which the bullet begins to yaw and its trajectory is affected. Shooting the rifling out of an M16 so that its bullets would tumble is about the most ridiculous thing I've ever heard relating to 5.56mm terminal ballistics. Flesh is typically 600 times more dense than air and a 5.56mm projectile, whether it's rotating at 1 turn in 7 inches or 1 turn in 12 inches will be rendered immediately unstable in flight. Whether it tumbles and fragments like the projectile of yore is dependent on its velocity, bullet construction and the medium it's penetrating far, far moreso than its rotational speed. 55 grain M193 ammo is just as effective when fired from a barrel with a 1/7" twist as it is when fired from a 1/9" twist and when fired from a 1/12"... there is no practical difference assuming velocity is the same.

HTH,
vanfunk
 
That's about what I thought.
Match the bullet weight, velocity, and barrel twist, and you can do much better.
Denis
 
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