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View Full Version : Ah! rumors about the early M16's "unstable bullet"


CrazyLarry
July 9, 2006, 08:52 AM
Venturing throught gun shops lately, I came across a Vietnam-era replica AR-15. The owner then began to spout off how that is truly what the M16 is all about, no charging handle/brass deflector so it is truly light, and a barrel twist that makes 55gr bullets lethal. This particular AR was chrome lined, but otherwise it was just like a Vietnam era rifle (sans full auto).

Then I come on here and read somwhere in here.....I believe:
http://www.ammo-oracle.com/body.htm
That this is all gunshop BS and that the bullet design is what makes a bullet unstable, not the twist rate. Rumor dispelled becuase we are scientists etc. etc.

Well, today at work I asked one with experience. A guy I work with, Tom, served in Vietnam from 65-66. When I questioned him about this ever holding true, he said that indeed, the bullets were unstable. he told me of hitting guys running in the upper shoulder (entry) and then seeing the exit wound come out of their lower abdominal, blowing out intestines. Tom claimed the rifles weren't bad, just kept it clean and never had any real problems with it. However, he did say the ammunition was crappy, that the brass was very thin and "soft." Due to this he claimed that when they were resupplied they would often dump live ammo (the old stuff they had carried)in the field to get rid of it. This they did by burying in fox holes as they left, but Tom said when they came back to these old sites the fox holes would be dug up. anyways, supposedly if they got the slightest rust/corrosion the ammo would really jam.

Also stated that while guys bitched about getting the M14s back, he loved carrying 800-1000 rounds of ammo on himself. And BTW, he was airborne and truly saw a lot of combat, also getting wounded i.e. this is a pretty reliable source.

Just thought it was interesting coming from first hand from him, great guy to listen to.

Harley Quinn
July 9, 2006, 11:16 AM
Thanks for the information.:D

HQ

Bud Helms
July 9, 2006, 12:08 PM
... the bullet design is what makes a bullet unstable, not the twist rate. I don't think it's that simple. The twist rate determines a range of bullet weights for best accuracy. Given a bullet weight within the range determined by the twist rate, I suppose a poorly designed bullet could cause poor accuracy performance, but that would have to be a really crappy design. Jamming? I can't make that connection. As I understand the early AR story, there was defintely a mismatch between the bullet weight and the twist rate of the rifling.

Now, corroded casings! THAT could definitely cause some cycling problems.

More knowledge will undoubtedly stop by this thread and straighten me out. :)

Jim Watson
July 9, 2006, 12:31 PM
No spitzer bullet is stable in dense media like water... or meat.
The question is, does it fragment or "tumble" in a way that makes it more damaging? Viet Nam era M193 ammunition is said to break up at the cannelure; current M855 at the seam between lead and steel cores; IF the velocity is still high enough/range short enough. Farther out, you depend on the bullet yawing or "tumbling" to enlarge the wound.

The British found the very stable .303 FMJ roundnose less effective on Afghans et cetera than lead .577-.450s. So they tinkered around with the original cut-nose Dum-Dum and several successive marks of expanding bullets to the point that they had to assure the early meetings at the Hague that they would maintain inventories of FMJs for declared wars against "civilized" nations, and keep the hollowpoints set aside for shooting at savages.

Their traditional Continental adversaries and allies begged to differ and the British gave up on that plan.

This all became academic when everybody started going to spitzer bullets based on the French Balle D and found that the pointed bullets would turn over on impact and make a wound nasty enough for any purpose. The British enhanced the effect with a light insert in the jacket nose of the Mk VII bullet.

Hard Ball
July 9, 2006, 12:45 PM
The original 1 in 14 twist was more lethal than the later 1 in 12 twist which is more lerhal than the current 1 in 9 inch twist.

Double Naught Spy
July 9, 2006, 01:05 PM
he told me of hitting guys running in the upper shoulder (entry) and then seeing the exit wound come out of their lower abdominal, blowing out intestines.
...
BTW, he was airborne and truly saw a lot of combat, also getting wounded i.e. this is a pretty reliable source.

So Tom is there in 'nam. There is an enemy running along and 1 and only 1 soldier fires a single shot at the running man and he is hit with one round going in the upper shoulder and his intestines are blown out his lower abdomen with M193 ammo? It has to be only one guy firing as that would be the only way to know that the shoulder round is the round bursting out the intestines

They don't make ammo like that anymore.

I spoke with a guy who served in the late 60s. After I purchased my first AR15, he told me how the ammo was designed to "crawl around inside the body." If you shot a guy in the arm and it hit bone, it would crawl up the arm, following the bone, thereby doing more damage than had it just passed through.

I honestly don't think many soldiers ever really knew the design history of the firearm or ammo while in 'nam. As with other wars, I don't doubt they were told many things about the superiority of the firepower and such, but a lot of it wasn't completely true.

El Paso Joe
July 9, 2006, 01:06 PM
I vaguely remember on my last "all expense paid vacation" to the Far East (1972) that I ran across the formula for twist and stabilization in a Gun Digest Treasury (I no longer have it - it bit the dust in one of my divorces...). I ran the numbers for a 55gr pill at 3200 fps in a 1 in 12 or 1 in 14 twist (I don't remember which) and I think the result was that it would stabilize a bullet 1.4 inches long... Unfortunately there was no formula to tell when the bullet was "over stabilized" but my hunch was that at that rate of twist, it was.

The next point is basic Physics 101 - conservation of energy. By the time the bullet (and fragments) all come to rest, all the energy must have been used to do "work" - and that includes rotational energy from a high rate of twist. This "work" usually resulted in damage to the target.

A good rule of thumb for stabilization is Greenhills Formula (I don't think that was the one I used in 1972) - If you Google it on the web you can probably find it and some good commentary.

Harley Quinn
July 9, 2006, 01:28 PM
Plan A does not normally work, so go to plan B. But, then Plan C may be the best, when all is said and done.

Soft tissue vs hard objects (vest or flak Jac, helmet). I believe if you want something to go through steel then it better not be in a yaw. I'll take a straight shot, over a beer.

http://ghlin2.greenhills.net/~apatter/general.html

HQ

JR47
July 9, 2006, 02:08 PM
The original M16 rifles of the early 1960's weren't nearly as accurate as the A1 or A2. At close range, though, the little rounds did tear things up. Much like the early reports of the Soviet 5.54x39 rounds. There were some documented close-range shootings that revealed the bullet taking a strange path. These were, unfortunately, usually from draftees attempting to leave the combat zone.

The rifles themselves were incredibly sensitive to powder fouling, the presence of corrosion in the unplated chambers, rough chambers straight from the factory, and the flimsy magazines issued at the time. The use of ball powder also resulted in a much higher than design firing rate, and buffer failures.

The flash-supressors, of the open-end type, were also difficult to manuver through the jungle without fouling on the undergrowth. We also found that the things would wick moisture up the barrel via capillary action during movement through wet foilage.

The rifles would also fail to drain quickly after immersion.

As to cleanliness. The initial instruction stressed how clean the weapons operated, and that the necessity for cleaning had been greatly reduced. They issued one cleaning rod for every three rifles!

I went through three M16 rifles in November of 1967. All but one failed due to bolt-over jams. The one that didn't was traded immediately prior to firing to an ARVN Ranger for his M2 Carbine, a bunch of 30 round mags, and most of a case of ammo.

In the end, I went back to my original M14 rifle.:) :)

MisterPX
July 9, 2006, 03:37 PM
So your Para buddy carried 1K rounds on him?
And somehow the ammo they carried was no good once they got "new" ammo which may have been older than what they had?

Just because they were there doesn't mean they know what they're talking about. As an example, we have a Ranger who is adamant that the AK47 is an open bolt gun.

Death from Afar
July 9, 2006, 03:45 PM
+ 1 Jim.

I have fired a lot - and I mean a lot- of mark 7 .303 ball at various critters over the years. My dad used to go mental if I ground the nose off to make them into crude hollowpoints due to the risk of jacket seperation in the barrel, so I was using the mark 7 load as issued. If it hit a bone it really did start to open up, but if it passed through without h itting a bone it was useless.

DPris
July 9, 2006, 04:28 PM
In '72 we were told the M-16 bullets tumbled on impact in USAF SP school.
In '94, I was doing a project with a 16-inch .223 and a 16-inch 9mm AR, part of which involved firing into my penetration box with several 8-inch squares of one-inch pine lined up about a half-inch between each one.
.223 55-grain FMJ tumbled as it passed through the boards and came to rest base forward. 9mm FMJ did not tumble, penetrated farther, and came to rest nose forward. Interesting enough, the 9mm AR was slightly more accurate at 100 yards. Both ARs were Colt Lightweights.
I have not used the .223 on people (been lucky), and FMJ results do not necessarily translate to HP performance. There are a number of factors involved- bullet weight, rifling twist, velocity, and bullet construction are all included.
Denis

CrazyLarry
July 10, 2006, 02:39 PM
yeah I would probably opt for ammo straight off a helicopter and in the case still, compared to stuff i had been humping around in a jungle with for days on end.

Make sense??:eek:

MisterPX
July 10, 2006, 02:55 PM
It would only make sense if the ammo wasn't sealed or if they slept in penetrating oil.;)

CrazyLarry
July 10, 2006, 04:21 PM
and it was there and free......

DonR101395
July 11, 2006, 09:32 AM
The original 1 in 14 twist was more lethal than the later 1 in 12 twist which is more lerhal than the current 1 in 9 inch twist.

The current barrels are 1 in 7" twist on the M4.

calvinike
July 11, 2006, 09:38 AM
Those early M16 bullets must have been made by the same people who invented the JFK magic bullet.

Harley Quinn
July 11, 2006, 11:05 AM
I believe the whole thing was a major mistake (tumbling bullets etc.).
They finally figuered it out, at the cost of many lives (expendable comes to mind).

The Department of War must have figured that one out also. Very slowly though. (Absolute screw up, the whole thing. A majorl scar on the US and the servicemen who had to go through it and give their life for the mistake's made).

Robert McNamara and his war was a Cluster fxxx from the get go. IMHO. Then they put him in charge of the World bank. Go figure:eek:

HQ

HorseSoldier
July 11, 2006, 11:56 AM
Robert McNamara and his war was a Cluster fxxx from the get go. IMHO. Then they put him in charge of the World bank. Go figure

That's the Kofi Annan school of management (i.e. see Bosnia, Rwanda, and then Kofi's promotion to Sec Generalship . . .). In jobs where you can manage to be held unaccountable for anything you do, no matter how utterly disastrous, how can one help but move on up?

DPris
July 11, 2006, 12:19 PM
A tumbling bullet, as it penetrates live tissue, is actually desirable in a light FMJ bullet in that caliber and in that role. It does much more damage in passing than an FMJ that doesn't. Think about it. Remember, this tumbling starts after initial penetration. The entrance hole is a perfect circle, like any other type of bullet would be. The tumbling was not a major flaw of the M16 system.
Denis

CrazyLarry
July 11, 2006, 03:10 PM
didn't Stoner design it with this purpose in mind? i.e. to tumble? Much like the AK-74 nowadays

BUSTER51
July 11, 2006, 04:03 PM
THEY WERE 1 IN 12 twist ,and as long as you use 55 grain ammo they stabilize just fine .Any problems with the early M16's were the falt of 2 a$$holes 1 named Kennedy and the other named McNamarra ,they changed mr Stoner's spec's and took off the chrome lined barrel and chamber .they fu*ked up the ammo and tryed to use left over powder the gov had in stock .once they went back to spec no more problems .Mr Stoner and Armalite did a fine job ,if those 2 idiots didn't **** in the soup there would have never been a problem .you keep them clean and oiled and no problem .some folks are lazy pigs and don't take of thier weapon and have problems .I used said issued weapon (1971/1972)and i never had a problem .

WhyteP38
July 11, 2006, 04:13 PM
That's the Kofi Annan school of management (i.e. see Bosnia, Rwanda, and then Kofi's promotion to Sec Generalship . . .). In jobs where you can manage to be held unaccountable for anything you do, no matter how utterly disastrous, how can one help but move on up?How? Well, if you did your job right, you'd probably be booted ASAP. The last thing a criminal syndicate wants is an honest man.
he told me of hitting guys running in the upper shoulder (entry) and then seeing the exit wound come out of their lower abdominal, blowing out intestines.
I find this hard to believe. Were these guys hit from straight ahead, at an angle while passing, or straight from the side? If from straight ahead or at an angle, the bullet must have had a lot of momentum to make such an abrupt change in direction and still blow out someone's intestines. If straight from the side, the bullet must have had a lot of momentum to power past bone, tendons, and muscle, then head south and still blow out someone's intestines.
when they came back to these old sites the fox holes would be dug up. anyways, supposedly if they got the slightest rust/corrosion the ammo would really jam.
Something must have gotten garbled in transmission. Why would anyone bury ammo they felt was crap, and then dig it up later and use it when it was certainly crappier after being buried, especially in a rifle where cleanliness is highly important to proper functioning?

CrazyLarry
July 11, 2006, 04:37 PM
Our guys would bury the crap ammo, and when they left VC/NVA whatever would supposedly dig up their old fox holes

CrazyLarry
July 11, 2006, 04:38 PM
THEY WERE 1 IN 12 twist ,and as long as you use 55 grain ammo they stabilize just fine .Any problems with the early M16's were the falt of 2 a$$holes 1 named Kennedy and the other named McNamarra ,they changed mr Stoner's spec's and took off the chrome lined barrel and chamber .they fu*ked up the ammo and tryed to use left over powder the gov had in stock .once they went back to spec no more problems .Mr Stoner and Armalite did a fine job ,if those 2 idiots didn't **** in the soup there would have never been a problem .you keep them clean and oiled and no problem .some folks are lazy pigs and don't take of thier weapon and have problems .I used said issued weapon (1971/1972)and i never had a problem .

also my understanding.

WhyteP38
July 11, 2006, 04:41 PM
Interesting. Since the ammo was a caliber they couldn't use, did they dig up the ammo for the components? It's difficult to see how the ammo would help them, unless they used the components for some sort of anti-personnel IED.

CrazyLarry
July 11, 2006, 04:44 PM
most likely for rifles they had stolen through working on base maybe or picked up after a firefight. They had plenty of our rifles :eek:

HorseSoldier
July 11, 2006, 04:46 PM
My understanding is that the VC were pretty opprotunistic as far as weaponry goes, including stuff captured from US or ARVN units, so they probably could find some use for 5.56mm ammunition if it was remotely servicable.

Edit to add, "What CrazyLarry said."

WhyteP38
July 11, 2006, 05:12 PM
Interesting. I've read several accounts from 'Nam vets claiming the VC and NVA avoided picking up M-16s because of the supposed problems with the gun and the round at that time. However, those accounts were also written by vets who didn't like the gun and the round, so maybe their accounts were mostly BiaSed.

JR47
July 11, 2006, 07:39 PM
The NVA weren't as interested in our weapons as the VC. The VC were pretty much equipped with hand-me-downs. They'd take just about any functioning arm. The NVA were a trained military force, with better logistics, and tended to use Soviet arms pretty much exclusively.

After the '68 Tet Offensive, the VC ceased to exist as a combat arm.:)

BillCA
July 11, 2006, 08:36 PM
As I recall, the original M16 cartridge was manufactured using DuPont IMR extruded bar powders (4895 & 3031 IIRC). With this powder the M16 ran clean. At some point the powder was changed to a ball powder (Olin/Winchester) I think for various reasons (my memory is fuzzy here). The ball powder was easier to load and they were able to add more powder to up the velocity of the round.

Unfortunately, the ball powders caused secondary fouling problems. Late in the war it was determined that the calcium content in the ball powders was too high and that caused sticky extraction, gummed up the gas port & tube and lowering the reliability of a dirty weapon.

According to Speer, circa 1974, the original M16 had a 1:14 twist rate which DoD found didn't stablize the boattail military bullet sufficiently at long range so a 1:12 rate was adopted.

Art Eatman
July 12, 2006, 09:50 AM
There was an excellent article during the 1990s in Soldier of Fortune magazine about the whole political deal for the M16 and its ammo.

Yes, originally the cartridge used an IMR powder; the cyclic rate was designed for it at around 700 rounds per minute. Yes, Olin's political efforts led to the use of ball powder--which increased the rate of fire by around 200 rounds per minute.

I don't recall the details about the bullets; I remember there was some discussion of the two-projectile bullet.

I bought one of the first Mini-14s, whenever it was they first came out. Some guys I knew at Fort Hood through sports car stuff would occasionally "liberate" some "extra" 5.56 FMJ ammo. I noticed that at close range the bullet would blow up and fragment on jackrabbits. Say within 50 yards. Well, let me waffle a bit and say that the exit wounds resembled those from a Sierra 52-grain HPBT. Trying to find and examine the bullet leftovers was nowhere near being a priority...

Art

Art

WhyteP38
July 12, 2006, 10:16 AM
I still have a hard time believing the "blowing out intestines" from a shoulder hit statement, for the reasons I mentioned previously.

CrazyLarry
July 12, 2006, 11:11 AM
hitting a guy while running, in the back.....would mean you shot him while he was running away from you, much like the shot Tom Berenger pulls with a short burst in the movie platoon. why is it so hard for you to see a bullet tumbling down like this? anything else you need to nit pick?

226
July 12, 2006, 11:20 AM
No charging handle? You probably mean forward assist?

The owner then began to spout off how that is truly what the M16 is all about, no charging handle/brass deflector so it is truly light,...

http://m14firinglineforum.com/upload/images/smilies/NAVY1.gif

CrazyLarry
July 12, 2006, 11:54 AM
yeah forward assist

WhyteP38
July 12, 2006, 12:42 PM
hitting a guy while running, in the back.....would mean you shot him while he was running away from you, much like the shot Tom Berenger pulls with a short burst in the movie platoon. why is it so hard for you to see a bullet tumbling down like this? anything else you need to nit pick?It's not a nitpick. It's the only type of wound you referred to in your original post, and it's the only support offered for the thread's topic: the M-16's "unstable bullet." In fact, the rest of the post about crappy ammo is irrelevant to the topic, and the discussion of VC/NVA grabbing US weapons is a tangent.

Your original post said nothing about hitting a guy in the back while he was running away. It said "running." That could be someone running toward you, past you, or away from you. That's why I asked about the direction in my first post. However, now that you state it, I still don't understand how that particular type of hit caused that particular type of wound.

I'm not saying and have never said it didn't happen. I have said and am saying that I don't understand the dynamics involved, because it seems to me the bullet would have to do four things that, taken together, seem improbable:

1) A forward-moving 5.56 bullet enters the target's upper shoulder. Assuming relatively even ground between shooter and target, the bullet impacts either on a flat or--given the relative height differences between American and Vietnamese men--very slightly downward angle.

2) The previously forward-moving 5.56 bullet takes a drastic turn downward. Normally, I would expect the bullet to fragment, go through the shoulder, or lodge in the shoulder. But okay, let's say the bullet or a fragment of it moves downward at a roughly 45-degree angle (it may actually be a greater angle, but it shouldn't be less).

3a) It must traverse a path of about 14 inches through the shoulder joint, past the rib cage, and into the intestine area. It must somehow miss the shoulder joint--no mean feat given the hit in the upper shoulder--rib cage, both, or hit one or both. And that is assuming it misses the shoulder blade.

or

3b) If the 5.56 bullet hits the upper shoulder but does not travel internally, it must exit the shoulder and then somehow re-enter the target.

4a) A downward-deflected 5.56 bullet/fragment misses the shoulder joint and rib cage, reaches the intestine area, and changes direction again into a forward-moving bullet/fragment that has enough momentum to exit the lower abdomen and blow out the intestines.

or

4b) A downward-deflected 5.56 bullet/fragment hits either the shoulder joint, the rib cage, or both but powers through rather than deflecting, reaches the intestine area, and changes direction again into a forward-moving bullet/fragment that has enough momentum to exit the lower abdomen and blow out the intestines.

I have a hard time understanding how this could happen once, but since your original post stated "he told me of hitting guys [plural] running in the upper shoulder (entry) and then seeing the exit wound come out of their [plural] lower abdominal, blowing out intestines," this type of hit supposedly happened more than once. These dynamics seem remarkable to me.

Art Eatman
July 12, 2006, 02:50 PM
Well, bullets can hit bone and deflect; a major portion can wind up almost anywhere in a body.

One of Charles Whitman's bullets--granted, a 6mm Remington--hit a guy in the right shirt pocket. The bullet deflected off a rib, downward through the right lung and through the stomach into the intestines. At 420 yards.

Art

Al Thompson
July 12, 2006, 03:00 PM
I've witnessed via autopsy (on critters) bullets do strange things when bones are hit. You may not be aware that the intestines will protrude with just a small cut - seen that a time or two as well. :barf:

One of my platoon sgts was in the 173rd in "Nam and would agree with Crazy right down the line.

CrazyLarry
July 12, 2006, 03:39 PM
<Art Edit>

I asked Tom if he ever saw bullets coming in one place and exiting in another strange location, so he gave me that example from his personal experience. As I recall he claimed to have seen that happen twice, and then I didn't care to REALLY elaborate on it since as a vet he might no want to recall all of the people he may have killed at 530AM on a Sunday morning.

If the shooter had higher ground (maybe even flat?) I don't see any huge fallacy in his statements

WhyteP38
July 12, 2006, 04:13 PM
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>

Demon5Romeo
July 13, 2006, 11:28 AM
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.

WhyteP38
July 13, 2006, 12:05 PM
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.

BigG
July 13, 2006, 12:55 PM
As I recall from The Black Rifle, (http://www.epinions.com/content_66857242244) 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.

Warbow
July 13, 2006, 02:37 PM
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.

davlandrum
July 13, 2006, 04:30 PM
Warbow - now I know why I flunked physics.....my eyes melted just reading that....

JR47
July 14, 2006, 01:21 PM
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.:)

Harley Quinn
July 14, 2006, 02:57 PM
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

DPris
July 14, 2006, 04:24 PM
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

BUSTER51
July 14, 2006, 05:09 PM
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:

Harley Quinn
July 14, 2006, 05:39 PM
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

44 AMP
July 14, 2006, 06:46 PM
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!

Lawyer Daggit
July 16, 2006, 12:46 AM
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.

Warbow
July 16, 2006, 11:40 PM
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.

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.

Fragmentation of M193 will occur the same whether fired from a 1:14" barrel or a 1:7" barrel.

U.S.SFC_RET
July 17, 2006, 12:43 AM
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.

DPris
July 17, 2006, 10:30 AM
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

vanfunk
July 17, 2006, 04:41 PM
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

U.S.SFC_RET
July 19, 2006, 03:53 PM
We all couldn't hit crap past the 200 meter target to be sure.:mad:

DPris
July 19, 2006, 04:58 PM
That's about what I thought.
Match the bullet weight, velocity, and barrel twist, and you can do much better.
Denis