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Old June 4, 2009, 09:25 AM   #1
Bartholomew Roberts
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Use of 5.56 M193 or M855 for self-defense and "Fleet Yaw"

I noticed in several of the recent "5.56 for home defense" threads that some posters mentioned they used XM193 or XM855 as their home defense load. There is some recent research on a concept called "fleet yaw" that people using these loads will probably be interested in reading.

Short summary: M193 and M855 do not yaw reliably. Dr. Fackler has been quoted as saying that 25% of the time, M855 or M193 fails to yaw and/or fragment, even when it has sufficient velocity to do so. Recent research cited by Dr. Gary K. Roberts has demonstrated a phenomenon that may help explain this called "fleet yaw."

Quote:
"Fleet Yaw is the other significant yaw issue discovered by the JSWB-IPT. Fleet Yaw is the terminal performance variation caused by inherent variability in each rifle and occurs in all calibers. 5.56 mm FMJ appears to suffer more Fleet Yaw induced variability than other projectile calibers & types. 6.8 mm OTM’s appear to have less Fleet Yaw variations than other projectile calibers & types tested.

What this means is that two shooters firing the same lot of M855 from their M4’s with identical shot placement can have dramatically different terminal performance results: one shooter states that his M855 is working great and is effective at dropping bad guys, while the other complains his opponent is not being incapacitated because M855 is zipping right through the target without upsetting. Both shooters are telling the truth."
M193 and M855 show the worst variations in Angle of Attack and Fleet Yaw. If you are using these for home defense, it may be worth your time to verify that the rounds do in fact yaw and fragment in your particular barrel. If you want to minimize Fleet Yaw problems without conducting your own experiments, then ammunition selection can help by either:

1. Using rounds with thin jackets and consistent production (OTM)
2. Using rounds that do not rely on yawing and fragmentation in order to be effective

Also, take some time to read the link. It is an education on terminal ballistics in a short Powerpoint that is well worth your time if you have even a passing interest in the subject.
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Old June 4, 2009, 11:59 AM   #2
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I have seen this on one occasion when I was expecting different results using M193 spec ammo. Hit a coyote with two shots. One went through it and nothing happened, the other left a cone shaped exit wound. The latter shot took it down very quickly.
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Old June 4, 2009, 06:03 PM   #3
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That explains some of the comments I got from my NCOs when I was on active duty. Those comments could be summed up as "when the 5.56 worked, it worked well, when it didn't work it was like poking small holes through them".

Frankly, the more I read WWII history, the more the fact that nothing works all the time is reinforced. Lots of failures then are glossed over by time and selective memory.
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Old June 4, 2009, 07:34 PM   #4
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Quote:
Frankly, the more I read WWII history, the more the fact that nothing works all the time is reinforced. Lots of failures then are glossed over by time and selective memory.
Careful, we don't want to whip the .30cal only rifle advocates into a frenzy. They don't like it when someone suggests that their .30cal battle rifles are not equivalent to ray guns!!
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Old June 4, 2009, 08:07 PM   #5
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I think my most jaw dropping experience was popping a duiker with a .375 H&H 270 grain softpoint and watching it run off. It didn't run far, but if it had been a haji with a grenade, I'd have been toast.

(shot placement was spot on, that duiker obviously was not up on his ballistics)



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Old June 4, 2009, 08:21 PM   #6
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There are definitely better and worse batches of ammunition on the .mil side of things. Part of the benefit of Mk 262 is that it's built to tighter tolerances and more consistent.
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Old June 4, 2009, 08:53 PM   #7
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I would suggest that the phenomena would be caused by something other than the rifle such as the bullet being slightly off its seat due to mishandling or mass manufacturing. A cartridge dropped on the floor could cause the tip of the bullet to become malformed and possibly move the bullet a thousandth or two from being concentric with the case. Considering the speed and rotational values either or both could cause changes in flight and terminal results.

NATO adopted the FMJ for the purpose of reducing battlefield deaths after the general public grasped the totals of WW I. This and the outlawing of gas changed the face of warfare for the civilized world. Commanders had also figured out that a wounded man took a lot more resources than a dead one.

Back to the 5.56 in the home. It takes about 20 meters for the bullet to stabilize so unless you have a really big house there is no telling what will happen.
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Old June 4, 2009, 09:39 PM   #8
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Quote:
There are definitely better and worse batches of ammunition on the .mil side of things. Part of the benefit of Mk 262 is that it's built to tighter tolerances and more consistent.
+1 and that would go for any match rounds.

I really like the 68gr OTM's by Hornady. Excellent accuracy and good terminal ballistics.
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Old June 4, 2009, 09:56 PM   #9
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The adoption of "controlled pairs" was meant to deal with this.

In the words of Capstick, "If it's worth shooting once, it's worth shooting twice." and "In the grand scheme of things, an insurance shot is only the price of a bullet."

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Old June 5, 2009, 01:49 AM   #10
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i dont understand why "civilians" use fmj's for self-defense....i never signed the geneva convention, thats why my self-defense mags are loaded with 55gr v-maxes or hornady TAP ammo.....fmj is what i use for plinking cuz it is cheaper, but when its four legged varmints it is the 55gr v-max and when it is 2 legged varmints it is TAP.
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Old June 5, 2009, 03:18 AM   #11
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Quote:
geneva convention
Wrong convention.

Secondly, NATO spec rounds are actually not bad inside 100 yards.
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Old June 5, 2009, 06:31 AM   #12
Bartholomew Roberts
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Quote:
I would suggest that the phenomena would be caused by something other than the rifle such as the bullet being slightly off its seat due to mishandling or mass manufacturing. A cartridge dropped on the floor could cause the tip of the bullet to become malformed and possibly move the bullet a thousandth or two from being concentric with the case. Considering the speed and rotational values either or both could cause changes in flight and terminal results.
Except that in order for your suggestion to be plausible, all of the dropped/malformed ammunition would have to end up in one rifle in order to alter the rate of yaw that dramatically. Considering that they have observed the phenomena universally across different cartridge types and calibers, I don't see how you could continually get those results if it was strictly an ammunition only issue.

Quote:
NATO adopted the FMJ for the purpose of reducing battlefield deaths after the general public grasped the totals of WW I.
NATO didn't exist until around 1949, so I really have to question how much its choice of projectile was influenced by WWI. Also the Hague Convention prohibiting the use of expanding bullets (which the United States did not sign) entered into force in 1900. The second Hague Convention which prohibited projectiles "calculated to cause unnecessary suffering" (which the United States did sign) entered into force in 1907. So I also question how either of these could have been influenced by WWI. Not to mention, all of the nations fighting in WW I were already using projectiles consistent with those conventions, so the idea that continuing to use them would somehow mollify the public strikes me as a strange one too.

In any case, probably a better topic for a separate thread since there is no relation to the subject at hand in any of that.

Quote:
Back to the 5.56 in the home. It takes about 20 meters for the bullet to stabilize so unless you have a really big house there is no telling what will happen.
Most of the laboratory test shoots of gel take place at distances of 10 yds or so and scientists seem to have no difficulty reproducing results at that distance, so it seems there is a fair amount of consistency in what happens under 20m.
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Old June 5, 2009, 11:44 AM   #13
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The use of non-expanding bullets comes from the British use of the Dum-Dum bullets (named for the arsenal in India where they were manufactured) in the Zulu and Boer wars in South Africa. They tended to do massive damage when hitting non-critical areas of the body.

Now my quick thought on the variation in yaw performance based on identical guns (this may be covered somewhere else) is that it may be somehow related to the heating of the barrel changing the performance of the rounds as the barrel expands/contracts. If this changes the fit of the bullet, then you get less spin, more yaw. The tendency of a bullet to wander after impact is largely related to the lack of angular momentum gained by spinning the bullet (this effect is why rifling works). The more spin, bullet radius, or mass, the larger the angular momentum. Bullet weight matters because it both increases mass and decreases velocity (which reduces spin rate coming out of the same barrel).
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Old June 5, 2009, 05:11 PM   #14
Bartholomew Roberts
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My understanding is that the difference in yaw is linked to the rifle - as in one barrel will have 100% of rounds yaw, while a second barrel may have only 50% yaw (just an example, not actual numbers)

So if the yaw decreased/increased as the barrel heated up, you would expect to see it across the board for all rifle barrels as they all heated up; but it appears that only some of the rifles are displaying this tendency.

A key factor seems to be the angle of attack of the round on impact.
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Old June 5, 2009, 11:37 PM   #15
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I don't think it should surprise anyone that bullets hitting living beings behave less consistently than those hitting homogeneous test mediums. Ballistic gelatin and other tissue simulates are nice, but we have to recognize their limitations compared to striking targets of variable densities.
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Old June 6, 2009, 12:07 AM   #16
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Quote:
NATO adopted the FMJ for the purpose of reducing battlefield deaths after the general public grasped the totals of WW I. This and the outlawing of gas changed the face of warfare for the civilized world. Commanders had also figured out that a wounded man took a lot more resources than a dead one
Where do you guys get this stuff? Don't you read history books?

* Soft-point and hollow-point bullets were banned by the Hague Conventions in 1899, about 15 years prior to WWI.
* The use of poisonous gas was also outlawed under the same clause of weapons designed to increase the seriousness of injuries. The German military approved use of mustard gas because it is not poisonous, it just eats at moist tissues (lungs, eyes, sinuses, etc) to cause injuries.
* Military commanders had figured out that wounded people take two to carry them back a long time ago. The Romans had ways of dealing with the enemy wounded that would lie on the battlefield until dark then crawl back to camp and live to fight another day: they turned large dogs loose on the battlefield after they were done for the day. During the Middle Ages, commanders started to realize the psychological effect of crippled soldiers wandering around back home. We learned to exploit it as a tool, that's all.
* NATO was formed in 1949 to form a large unified miitary force to respond to the USSR's armed forces after the USSR started toppling small nations after WWII. That was about 30 years after the end of WWI.
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Old June 6, 2009, 01:11 AM   #17
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Obviously most of my information was wrong. I'm not a historian.

What I stated was what was often passed around the dinner table by my uncle (USMC, D-Day, Omaha Beach to Berlin), another uncle (Army, Anzio) and Dad (USN, Pacific). I heard it so many times that I assumed that it was correct and never followed up. I apologize for statements.

Let's get back on track. I'm still trying to wrap my head around the "fleet yaw" problem.
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Old June 6, 2009, 06:06 PM   #18
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If you're using an AR15 for HD why aren't you using soft points?
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Old June 6, 2009, 10:11 PM   #19
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Quote:
If you're using an AR15 for HD why aren't you using soft points?
Because I am happy with the performance of XM193 and 68gr Black Hills OTM.
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Old June 6, 2009, 11:26 PM   #20
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Have you considered any of the brands that use Barnes triple shock? Lots of expansion quickly
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Old June 6, 2009, 11:36 PM   #21
RockyMtnTactical
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Have you considered any of the brands that use Barnes triple shock? Lots of expansion quickly
I wouldnt use anything over the 68gr OTM Nosler other than the Mk262 Mod1 Sierra 77gr MK, Nosler 77gr, or Hornady 75gr OTM bullets.
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Old June 7, 2009, 08:52 AM   #22
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Quote:
If you're using an AR15 for HD why aren't you using soft points?
I used to say the same thing. Always kept mine loaded with some kind of expanding bullet. But it turns out that M193 is _usually_ better if you are going to be shooting people. It would take pages and pages to explain and that's what this site is for: http://ammo.ar15.com/ammo/

Just don't get confused and go out and buy some generic FMJ ammo. You want true military M193.

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Old June 7, 2009, 10:36 AM   #23
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Given the "defense" part of home defense, I figure that whatever ruins Wily Coyote at a hundred yards most likely won't be salubrious for people at five to twenty yards. Mr. Sierra is real helpful for that...
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