223 vs 5.56

[JohnKSa]

Right now, you believe that you have the truth because you trust the sources you've trusted.

You have completely missed the point. While it is true that I (as anyone should) have more confidence in the warnings provided by multiple ammunition companies and idependent experts than I have in theories provided by anonymous folks on the internet, that is really a secondary issue.

The primary issue has more to do with addressing your objections to the warning/explanations to the sources, and especially the shaky "logic" you have used to defend those objections and the theory you have proposed.

That you are getting angry or frustrated means that somehow I'm challenging you to actually think in a way that is uncomfortable for you...

I'm not angry, and to the extent that I'm frustrated it is not because you have challenged me to think differently. It is because you:

1. Don't seem to see how logically bankrupt some of your reasoning is.
2. Repeately raise the same issue over and over again even after it has been definitively addressed. (more on that later in this post)

...I base my understanding on the actual evidence available (hearsay is not evidence).

This is, of course, not true since you have already admitted that you have no "actual evidence" to show that secondary pressure spikes have caused popped primers in ARs. You have theorized that they might, and have gone so far as to say that it's a more likely explanation than the one provided by the ammunition companies and experts, but you have, admittedly, done so in the absence of any "actual evidence" showing that any AR has ever popped a primer as the result of a secondary pressure spike.

I don't have the data to prove the conventional wisdom true...

Which means ONLY that you, personally, can not personally prove that the explanation provided IS true. It does not, in any way, give you the abilty to prove that the explanation is NOT true.

The inability to prove a premise is NOT equivalent to the ability to disprove that premise. The fact that I have no way to personally prove the existence of the Higgs Boson does NOT automatically mean I have disproved, or can disprove, its existence.

Furthermore, your lack of direct access to this data does not, in any way, call into question the warning/explanations provided by the ammunition companies and experts. Just like Frank Jones' lack of direct access to raw particle accelerator/collider data doesn't in any way call into question the explanation of the physicists who do have access the data and provided their conclusions.

But if we start quoting experts instead of data...

The idea that we can't accept anything as valid without looking at the data ourselves is ludicrous. As I mentioned earlier, if we get information from multiple, independent reliable and authoritative sources who all agree, it is reasonable to assume, in the absence of hard evidence to the contrary that the information is reliable.

If everyone had to prove everything for themselves, if everyone had to examine the raw data for themselves, the field of human endeavor would have stalled long ago when it became impossible for one person to be able to understand all of science and technology sufficiently to prove/examine everything personally before relying on it.

...we are simply falling prey to the "argument from authority" fallacy which doesn't do anyone any good.

Getting back to the second source of frustration mentioned above, there are at least two more examples from this latest post. This quote is one.

On page 2 of this thread, you made a similar comment about the "argument from authority" fallacy and I pointed out that your understanding of the fallacy is incorrect and provided some links and quotes that explained the correct meaning of the argument from authority fallacy.

That basic pattern has been a theme on this thread. You raise an issue and it is definitively addressed and yet you go on as if that never happened, raising the same issue again, sometimes only a few posts later, as if it were a new objection.

...focused on "this should not happen in a tight bore barrel 20" or less." to accuse me of not reading my own source data.

Here's another example. As I have already pointed out, at least twice previously, the quote is that "SEVERE" secondary pressure spikes should not occur in barrels 20" or less. Yet, in spite of that, you have raised the same objection again as if I had not already addressed it accurately.

 

[Jimro]

JohnSKa,

1, You can't show a pressure trace showing anything more than a normal, repeatable expected rise in the primary pressure curve from a mismatch.

2, I can show data showing secondary pressure spikes late in the firing cycle with 5.56 chambers, and a severe secondary pressure spike in a worn match AR.

Your objections to the secondary pressure spike data is that in the 5.56 data from lucky gunner it wasn't high enough, and that in the shootingsoftware.com it was with a match rifle. My response is that if the pressure coincides with extraction that even normal pressure can pop a primer out (in fact a partially popped primer in a bolt action rifle is associated with a low pressure event) and that the source noted that "this can happen in any rifle in any caliber" and hedged their language noting that "severe secondary pressure spikes shouldn't happen in a 20 inch or less tight bore barrel." So a less than severe pressure spike at the right time in the extraction cycle could give you a popped primer when the bolt face is not supporting the primer.

This explanation fits the facts and data available, without any missing pressure.

The alternate "common wisdom" explanation is that the extra friction of the leade spikes pressures to over 85k psi which expands the case head and causes the primer to go flying out on extraction. But we don't have any actual recordings of this happening, and only data showing a repeatable, not dramatic increase in pressure.

That still leaves us with math not adding up, where is the pressure coming from that is popping primers? The only actual data source we've seen that could do that is the secondary pressure spike reported with Winchester 55 grain ammunition.

And that is my "shaky" logic.

Now here is the kicker, I can't "prove a negative" which means that I can't prove that there won't be an event somewhere at some time that isn't solely due to a mismatch.

Jimro

 

[JohnKSa]

1, You can't show a pressure trace showing anything more than a normal, repeatable expected rise in the primary pressure curve from a mismatch.

1. Irrelevant. Since the warnings do not originate from me, the fact that I do not have access to the pressure trace data in question means nothing. If you can prove that the ammunition companies have made the warning in the absence of any pressure data to support the warning, THAT would be relevant.

2. This objection has already been raised and answered multiple times on this thread.

2, I can show data showing secondary pressure spikes late in the firing cycle with 5.56 chambers, and a severe secondary pressure spike in a worn match AR.

1. Given that the pressure spikes are under SAAMI max in all cases involving barrels of 20" or less, it is a mischaracterization to call them severe.

2. Given that the pressure spikes did not result in popped primers or any other signs of overpressure events in barrels of 20" or less, it is a mischaracterization to call them severe.

3. This claim has already been made and answered multiple times on this thread.

My response is that if the pressure coincides with extraction that even normal pressure can pop a primer out (in fact a partially popped primer in a bolt action rifle is associated with a low pressure event) and that the source noted that "this can happen in any rifle in any caliber" and hedged their language noting that "severe secondary pressure spikes shouldn't happen in a 20 inch or less tight bore barrel." So a less than severe pressure spike at the right time in the extraction cycle could give you a popped primer when the bolt face is not supporting the primer.

1. Your theory seems plausible. It may well be that the secondary pressure spikes DO sometimes result in popped primers in ARs in spite of the fact that you have presented no data to demonstrate that it actually has or does.

2. If you ARE eventually able to document that secondary pressure spikes can cause popped primers in ARs, that will not disprove the ammo/chamber mismatch warning since the ammo/chamber mismatch warning does not claim that an ammo/chamber mismatch is the only possible source for popped primers or other overpressure events.

3. This point has already been raised and addressed multiple times on this thread.

That still leaves us with math not adding up, where is the pressure coming from that is popping primers?

1. It does not leave us with the math not adding up since there is nothing in the warning that precludes other contributing factors from increasing the pressure. Chamber temperature, high ambient temperatures, etc. can all raise discharge pressures. When you combine a number of factors which don't commonly result in severe overpressure, the combination of those factors are known to and can be demonstrated in some cases to sum and result in a pressure that is higher than the single contribution of any one of the factors in isolation. Combine that with multiple sources indicating that the mismatch alone can cause pressures in excess of 75K and you have a more than adequate and completely credible explanation for how the ammo/chamber mismatch can cause popped primers in a situation where they would not otherwise occur.

2. This objection has already been raised and answered multiple times on this thread.

(I'm not trying to be objectionable by pointing this out, but at some point, isn't enough enough? How many times do we need to cover the same ground before we decide the grass on it is really and truly trampled to death? It would be one thing if you could raise a new point or rebut the counterpoint; simply reposting a point that has already been put to rest doesn't benefit anyone at all.)​

...I can't prove that there won't be an event somewhere at some time that isn't solely due to a mismatch.

On a practical note:

Because we don't shoot our firearms in tightly controlled laboratory conditions where we can insure that there are no additional contributors which might raise pressures, there's no real-world benefit of being able to demonstrate that the ammo/chamber mismatch can't be the "sole" cause of an overpressure event.

The entire point of such warnings is that because it's not possible to control all the circumstances rigorously, it becomes more critical to control the things that can be controlled. The knowledge that the damage/injury from an overpressure event was due to multiple contributors and not just a single one would not be any consolation at all.

 

[Jimro]

Brian,

I'd like to remind you of the Armalite warning.

The first few rounds of ALL ammunition, from whatever source or lot, should be checked for signs of pressure or any other defect before firing large quantities. If you have a problem, you can generally bet that the ammunition meets neither SAAMI nor NATO specifications.

When there isn't a mismatch folks generally blame bad ammo. When there is a mismatch, folks generally blame the mismatch. It doesn't matter what chamber leade you have if the ammunition is bad.

To address JohnSKa's concern,

It does not leave us with the math not adding up since there is nothing in the warning that precludes other contributing factors from increasing the pressure. Chamber temperature, high ambient temperatures, etc. can all raise discharge pressures. When you combine a number of factors which don't commonly result in severe overpressure, the combination of those factors are known to and can be demonstrated in some cases to sum and result in a pressure that is higher than the single contribution of any one of the factors in isolation. Combine that with multiple sources indicating that the mismatch alone can cause pressures in excess of 75K and you have a more than adequate and completely credible explanation for how the ammo/chamber mismatch can cause popped primers in a situation where they would not otherwise occur.

Having a complete credible explanation is not the same thing as having actual data to prove the complete credible explanation. You say this is irrelevant. Let it be known that the NATO proof load for 5.56 is 77,958 PSI (537.5 MPa), and the proof load, intentionally overloaded, does not pop primers.

However since NATO specification calls for ammo to be tested at high temperatures to simulate a desert deployment, blaming temperature as a proximate cause for a chamber pressure spike is pointing to ammunition that would have failed NATO specification testing. You can check the NATO EPVAT testing criteria for yourself, suffice to say that it is rigorous.

Let me quote a DTIC report:

Within NATO small caliber ammunition standardization, the NATO Design Mark has no official significance. It is generally accepted that the ammunition with this mark should, but cannot be guaranteed, to chamber correctly in a weapon. It should not be assumed though, that it will produce the expected performance or necessary level of safety required by the STANAG and MOPI.

This is the reason why the Brits I met in Iraq told me that they could not use American Lake City M855 ammunition through their L85 rifles, but that we could use their SS109 ammunition made by Radway Green. Both are NATO weapons, both loads are "NATO Spec" but true interoperability was not achieved.

Jimro

 

[JohnKSa]

Let it be known that the NATO proof load for 5.56 is 77,958 PSI (537.5 MPa), and the proof load, intentionally overloaded, does not pop primers.

My last post (as well as several others I have made on this thread) already addresses this. Even if we are willing to accept that a proof load doesn't pop primers in ARs **, that assumption doesn't preclude the ammo/chamber mismatch from being the primary contributor in popped primers and other overpressure events since "we don't shoot our firearms in tightly controlled laboratory conditions where we can insure that there are no additional contributors which might raise pressures".

"Combine that with multiple sources indicating that the mismatch alone can cause pressures in excess of 75K and you have a more than adequate and completely credible explanation for how the ammo/chamber mismatch can cause popped primers in a situation where they would not otherwise occur."

**It is probably worth pointing out the source for this factoid that you have repeatedly stated as truth.

Unfortunately 77k psi won't pop the primers out. Case head expansion doesn't start until 85k psi according to Clark, who has tested more cartridges to failure than I care to count (and I believe him on this), and primers don't pop out until pressures are higher than that.

85k was the pressure noted by Clark in his tests.

No offense meant to Clark, but for research purposes, he is essentially an anonymous source. You have repeatedly taken me to task for citing the consensus of conclusions of multiple ammunition companies and other independent experts, making statements like: "Right now, you believe that you have the truth because you trust the sources you've trusted." and accusing me of "quoting experts instead of data".

I've tried to use other points to demonstrate that you are operating with a pretty impressive double-standard and are apparently not aware of it, perhaps this will resonate a little more strongly.

It appears that one of the major pillars of your theory is based on a quote from an anyonymous source. Using your own standards, you should not have relied on this quote unless you were in possession of the pressure trace data that the source used to demonstrate that 223/5.56 primers will not pop at 77Kpsi.

At the very least, using reasonable research standards, you should not have relied on it in the absence of corroborating evidence from authoritative and reputable sources.​

 

[Jimro]

JohnSKa,

Clark shared his data, and is available to answer clarifying questions. That is what a researcher would consider a "primary source" when conducting research. A secondary source is one such as a news article, textbooks, etc that interpret data/events from primary sources.

If you have a problem with his data, please let me know. His test rifle was a manual action falling block, which eliminated the gas system as a confounding factor.

Clark posted his results, you can find them here: http://www.thehighroad.org/archive/index.php/t-303359.html

If you wish, I'll stop talking data and simply start throwing counter expert arguments, like this one.


It’s long been accepted that a primer popping out of a case when a round is fired is an absolute indication of high pressure. This is usually referred to as “blown” primer. However, it can also occur because a gas-operated, semi-automatic rifle is not properly timed. In other words, the bolt unlocks before the case releases its hold on the chamber, and the primer pops out. It’s not an entirely unusual occurrence with AR-10s. Jeff Hoffman with Black Hills Ammunition refers to these as “dropped” primers.

.....

Bottom line: No matter the cause, blown, dropped or pierced primers are not normal. They’re an indication something is wrong. Remember, it’s not always high pressure or the ammunition. Believe it or not, sometimes our rifles, just like gun writers, are not perfect, either.

If you want me to prove that proof loads don't pop primers, I'd ask you to look at the bolt fact of centerfire Remington and Marlin rifles, as they are advertised as proof tested. If there is no gas cutting ring around the firing pin, then the primer didn't fail. If you find a new rifle with a gas cut ring on the bolt face, obviously it experienced a primer failure.

However, once again I can't prove a negative. It is impossible to say that a proof load won't blow a primer any more than I can't prove you've stopped beating your wife. I can say that proof load level pressures are not known to pop primers.

Jimro

 

[JohnKSa]

Clark shared his data, and is available to answer clarifying questions. That is what a researcher would consider a "primary source" when conducting research. A secondary source is one such as a news article, textbooks, etc that interpret data/events from primary sources.

Using your definition, ammunition manufacturers also clearly qualify as primary sources.

You can't simply accept any data that fits your conclusion and reject any data that does not. That isn't sound science/research. You need to apply the same standard of acceptance or rejection to the data regardless of whether it fits or doesn't fit your conclusion.

If you're going to reject data from some sources on the basis that you don't have their raw data to personally review, then you should apply the same standard to other sources.

If you're going to call one source a "primary" source and accept conclusions from that source without reviewing the raw data used to generate the conclusions, then you need to accept data from other sources that meet your defininition of "primary" sources without imposing the personal review requirements on their data.

If you have a problem with his data...

This is about the blatant double standard in your data selection criteria. If you had been objective in your data selection standard, YOU would have had a problem with his data.

If you wish, I'll stop talking data...

That's ridiculous. Nobody said anything about not "talking data". This is about being reasonable and objective in the methods one uses to select or reject data.

If you want me to prove that proof loads don't pop primers, I'd ask you to look at the bolt fact of centerfire Remington and Marlin rifles, as they are advertised as proof tested. If there is no gas cutting ring around the firing pin, then the primer didn't fail. If you find a new rifle with a gas cut ring on the bolt face, obviously it experienced a primer failure.

This paragraph contains two unjustified assumptions.

First of all, it assumes that all proof loads are maximum pressure proof loads, and second, it assumes that proof cartridges are identical to service cartridges with the exception of the pressures involved. In point of fact, both of those assumption are incorrect.

http://saami.org/specifications_and_information/publications/download/206.pdf

According to this SAAMI publication, in the .223 a load generating a pressure of 73.5Kpsi--well below the pressures we have been discussing is still an acceptable proof load.

However, an even more important point is noted in the publication.

NOTE: The heat treatment of cartridge cases for Definitive Proof Loads may be different from the treatment of service cases, at the option of the manufacturer.

Other case modifications to minimize firing casualties, such as gas leaks around primers are also permissible. The use of such options must not affect the stressing of the firearms components.​

In other words, SAAMI allows the manufacturers to take special precautions to insure that the proof loads do not damage the firearms under test via gas cutting. That fact:

1. Demonstrates that SAAMI acknowledges that blown primers are a likely result of proof testing.

2. Completely disproves the contention that the absence of gas cutting in new firearms is evidence that proof loads will not cause blown primers.

 

[Jimro]

JohnSKa,

You write "well below pressures we are talking about here" but cannot show those pressures. If you could, you would have by now.

Even if we take 62k PSI as a starting point (measured by CIP, which would be 55k measured by SAAMI), add 12k psi to get to 74k PSI (measured by CIP), we are still less than the 77k (measured by CIP) used a proof load for 223 Rem and 5.56 NATO.

Now if you start at 55k (measured by SAAMI), add 12k PSI (as measured by SAAMI) you get to 67k PSI (as measured by SAAMI) which is still 10% under the proof load of 73K PSI that you say.

Of course, if you want to take the 58k (5.56 pressure CIP standard) and add 12K PSI, you get to 70K PSI, which is perfectly in line with the ballistictools.com referrence for firing a 5.56 cartridge in a 223 chamber, which is still less than any of the proof load pressure levels.

As far as my double standard goes, I'm very glad you are an engineer and not a scientist, any primary source that won't share data must be weighted below a primary source that does share data when discussing data interpretation. No matter how trustworthy a primary source, if they don't show HOW they came to that conclusion then we are back to Aristotle ending an argument by saying, "The Master has spoken!" which is "argument from authority" and the weakest argument.

A weak argument is still an argument, I'm more interested in the data than the argument.

To prove your argument, you need to show a mismatch with a pressure curve elevated enough to pop a primer. If you do that, I will be very happy.

Jimro

 

[rebs]

I have fired both 5.56 and 223 in my colt and s&w sport with no problems at all. Some of it was LCD military ammo.

 

[JohnKSa]

You write "well below pressures we are talking about here" but cannot show those pressures.

Multiple sources, including some of your own indicate that the mismatch alone can result in pressures in the neighborhood of 77KPsi. You've tacitly accepted this figure for the entire thread--why are you rejecting it now?

You have admitted on multiple occasions on this thread that the mismatch can result in pressures equivalent to proof loads but have repeatedly claimed that proof loads won't pop primers. Now we have evidence that SAAMI knows that proof loads can pop primers and therefore allows gun companies to take steps to prevent that occurrence from damaging guns during proofing.

Now, suddenly you want to backtrack and claim that there's no evidence that the mismatch can cause proof load pressures. The numbers haven't changed, the facts haven't changed. The only thing that has changed is that now there's evidence that your claim that proof loads can't pop primers is false. It's not reasonable for you to now try to reject what you accepted before just because it no longer supports your premise. If you accepted it before, then from an objective and reasonable standpoint, you should still accept it.

It's not scientific, objective, reasonable, or logical to suddenly reject data/facts that you previously accepted and to reject it simply because new evidence brought to light shows that the previously accepted data no longer supports your premise. The data/facts are supposed to produce the conclusions, it's logically and scientifically bankrupt to allow the conclusion to drive the data selection process.

...any primary source that won't share data must be weighted below a primary source that does share data when discussing data interpretation...

This is grasping at straws.

You got caught accepting data from one source that clearly did not meet the standard you applied to other people's sources. Then you claimed your source was a primary source to attempt to cover the double-standard--unfortunately, the sources on the other side of the debate were also primary sources. Now you're claiming that some primary sources (namely yours) are better than other primary sources in an attempt to salvage your argument in the face of hard evidence showing that your data selection process was obviously biased.

If I were to point out that Clark has not shared any pressure curve data with you, demonstrating that your new attempt to defend your own primary source and reject mine is baseless; past performance indicates that you would find some new creative reason why Clark's conclusions are acceptable and the the ammunition companies' conclusions are not.

To prove your argument, you need to show a mismatch with a pressure curve elevated enough to pop a primer.

That is incorrect.

For me to convince you I would need to show that. At least that's what it would take right this moment--it seems fairly likely that if such data were to present itself that the requirement would change since you've already demonstrated that you will creatively find rationale to dismiss any evidence that doesn't agree with your premise (even evidence which you previously accepted as truth) and just as creatively find justification for accepting evidence that bolsters your premise (even when it doesn't meet the standards for evidence selection that you impose on others).

For anyone willing to objectively examine the evidence, this debate is over. By your own admission, we have multiple authoritative, primary sources which all provide corroborating conclusions and, on the other hand, we have no evidence at all demonstrating that secondary pressure spikes can pop primers in barrels under 20" in length.

Furthermore, the argument about whether or not secondary pressure spikes COULD possibly pop primers, even if proven, was not going to invalidate the warnings. As noted before, even if it IS true that secondary pressure spikes can pop primers, that still doesn't in any way disprove, invalidate nor even weaken the ammo/chamber mismatch warning since the ammo/chamber mismatch warning does not claim that an ammo/chamber mismatch is the only possible source for popped primers or other overpressure events.

Fortunately, logic does not require that the person on the losing side of a debate must be convinced in order for the argument to be proven. That is the case here. The argument is proven at this point regardless of your objections.

Fact: The mismatch can generate proof load pressures. (Even you accepted this as fact for the entire duration of the thread up until your last post when you realized it no longer supported your conclusion.)

Fact: Proof load pressures can pop primers. (SAAMI documention provides evidence.)

Conclusion: The mismatch can cause popped primers.

That's even before we get into adding in real-world practical issues like considering the effects of other contributing factors such as high ambient temperatures, etc. on the mismatch.

 

[Jimro]

JohnSKa,

Were those pressure traces at the luckygunner article or the shootingsoftware.com article?

I've had tabs open on two computers and I must have misplaced the evidence you claim I'm ignoring.

Also, please link, ISBN or any source to the SAAMI evidence of proof loads popping primers. It was my understanding that if a proof load popped the primer or suffered any other failure then the rifle failed proofing.

Now, I also have multiple sources saying that all the symptoms associated with the mismatch can be attributed to ammunition defects, and instances where these same "mismatch symptoms" happened in 5.56 chambers.

The mismatch doesn't explain those symptoms showing up in 5.56 chambers, now does it?

Jimro

 

[JohnKSa]

...the evidence you claim I'm ignoring.

You're not ignoring anything and I didn't say you were.

What I said was that when you realized that proof loads could actually pop primers, you immediately changed your position (which you had held for the duration of the thread) from accepting the fact that the mismatch could cause proof load pressures to rejecting it.

Also, please link, ISBN or any source to the SAAMI evidence of proof loads popping primers. It was my understanding that if a proof load popped the primer or suffered any other failure then the rifle failed proofing.

Please look at the pdf document on the SAAMI.org website from the link I provided. The quote immediately under the link is from that document. SAAMI allows the manufacturer to use specially heat treated cases and "other case modifications" during proof testing to prevent primers from popping.

Now, I also have multiple sources saying that all the symptoms associated with the mismatch can be attributed to ammunition defects, and instances where these same "mismatch symptoms" happened in 5.56 chambers.

This objection has been repeatedly addressed on this thread. It is irrelevant. The mismatch warning does NOT claim or even imply that the mismatch is the EXCLUSIVE cause of overpressure symptoms in .223 rifles. Therefore the existence of other issues which can cause similar symptoms in no way invalidates, weakens, or even calls into questions the accuracy of the mismatch warning.

The mismatch doesn't explain those symptoms showing up in 5.56 chambers, now does it?

Your attempt to prove that other things can cause overpressure symptoms or that overpressure symptoms can occur in 5.56 chambers as well as .223 chambers, has NO bearing on the validity of the mismatch warning. Since the mismatch warning only provides information about a SINGLE issue that can cause overpressure events (namely the ammo/chamber mismatch) there is nothing about the existence of other causes of overpressure events that calls the accuracy of the mismatch warning into question.

Going back to the stove analogy, the fact that you can burn your finger on a hot exhaust pipe doesn't mean that a warning about burning your finger on a hot stove is invalid. If you were warned that THE ONLY WAY to burn your finger was on a hot stove, then proving that you could burn your finger in other ways than on a stove WOULD prove that the warning was false.

However, if someone points out that touching a hot stove is one way to burn your finger, proving that you can burn it other ways doesn't have any bearing at all on whether the stove warning is accurate or not. It's a complete non sequitur.

In the same way, IF someone were to claim that the ammo/chamber mismatch were THE ONLY WAY to get overpressure symptoms in a .223, then proving that there are other methods of achieving overpressure symptoms in a .223 rifle would disprove the accuracy of the warning because that would prove it is not THE ONLY WAY.

But the mismatch warning does NOT claim that the mismatch is the ONLY way one can get overpressure symptoms in a .223 rifle. It only claims that it is ONE thing that can cause an overpressure event. Therefore proving that there are other things that can cause overpressure events does not call the accuracy of the warning into question in any way at all.

Finally, the fact that overpressure symptoms can occur in other caliber rifles than just .223 (5.56, for example) does not disprove the warning either. Many of the things that can cause overpressure events are not peculiar to a particular caliber--they can appear in any caliber. So while the 5.56ammo/.223 chamber mismatch issue can only show up in .223 chambers, any of the other overpressure causes can show up in pretty much any caliber out there. The contention that an overpressure symptom in 5.56 calls the validity of the warning into question is therefore also a non sequitur. There's nothing in the warning that suggests that overpressure events can only occur in .223 chambers OR that the only cause of overpressure events is the ammo/chamber mismatch.

 

[Jimro]

Just for reference.

Cartridge, 5.56mm, Ball, M193

Weight - 182 grains
Length - 2.26inches
Primer - Percussion (Crimped into case)
Propellant - WC 844 or CMR 170
Charge - 28.5 (WC 844)or 26.5 (CMR 170) grains
Projectile Weight - 56 grains
Chamber Pressure - 52,000 psi
Velocity - 3250 fps, 15 feet from muzzle

Cartridge, 5.56mm, Ball, M855

Weight - 190 grains
Length - 2.26inches
Primer - Percussion (Crimped into case)
Propellant - WC 844
Charge - 26.1 grains
Projectile Weight - 62 grains
Chamber Pressure - 55,000 psi
Velocity - 3025 fps, 15 feet from muzzle

SAAMI Reference http://www.saami.org/specifications_and_information/specifications/Velocity_Pressure_CfR.pdf SAAMI does not list a 5.56x45 pressure range. Since we cannot compare pressures due to the chamber differences we need to look at velocity as a proxy.

223 Remington:

55gr Projectile
3,215 fps nominal 15 feet from the muzzle
550 MAP, 564 Max Probable Lot Mean, 585 Max Sample Lot Mean (all numbers PSI/100)

62gr Projectile
3,080 fps, 15 feet from the muzzle.
550 MAP, 564 Max Probable Lot Mean, 585 Max Sample Lot Mean (all numbers PSI/100)

The M193 load exceeds SAAMI spec by 35 fps, the M855 load does not exceed SAAMI max velocity.

Federal lists 223 55 gr ammunition at 3,240 fps, exceeding SAAMI spec, and puts 5.56x45 in parenthesis http://www.federalpremium.com/products/details/rifle.aspx?id=69 and 62 gr ammunition at 3,020, only 5 fps from M855, http://www.federalpremium.com/products/details/rifle.aspx?id=71

Please compare the chronographed velocities of ammunition found here: http://www.ar15.com/content/page.html?id=213 and I think that the Federal ammo linked is clearly at the "milspec" level of performance, having the 55gr load chrono'd to 3038 fps from a 16" barrel, different lot 2980 from a 14.5" barrel. With that performance it is on par with M193 loads known to pop primers. Chrono reports here: http://www.ar15.com/mobile/topic.html?b=3&f=16&t=287820&page=2

It should also be noted that different lots of Federal AE 55 and 62gr 223 loads have come with uncrimped primers. http://www.surplusrifleforum.com/viewtopic.php?f=96&t=25953&sid=6c0491b211e61829d71dde6b3605a6ae

Please also note the two tests, Guatemalan M193 and Winchester Q3131 which exceed the US Milspec for M193 for velocity with a 20" barrel.

As Armalite put it before, if you you have an ammo malfunction, odds are the ammo was never spec'd to NATO or SAAMI standards.

Jimro

 

[Jimro]

JohnSKa,

Since the mismatch warning only provides information about a SINGLE issue that can cause overpressure events (namely the ammo/chamber mismatch) there is nothing about the existence of other causes of overpressure events that calls the accuracy of the mismatch warning into question.

Let me quote another primary source, one JonhSKa.

From the beginning it has been clear that the pressure rise due ot the mismatch is not spectacular although it is cause for concern. Because it is not a dramatic pressure increase, it often goes unnoticed EXCEPT when additional circumstances (such as high ambient temperatures, high chamber temperatures, etc.) cause an additional pressure increase on top of the pressure increase cause by the mismatch.

The JohnSKa position from reply #51 is that somehow this "not spectacular" pressure rise is concerning, even though no symptoms of overpressure are showing up except when "additional circumstances" increase the pressure on top of that. I respect your position, and mine is not far from it, that a chamber mismatch in combination with an ammunition failure to meet either NATO or SAAMI specifications will cause symptoms associated with a mismatch, and in 5.56 chambers it is an ammunition failure alone.

To be fair, we haven't really dug into to other conditions that can cause an over pressure like symptom such as bore condition, chamber friction, etc. But JohnSKa from post #51 seemed to think that those additional factors might be important, and so do I.

Jimro

 

[Bart B.]

Jimro says:

If you want me to prove that proof loads don't pop primers, I'd ask you to look at the bolt fact of centerfire Remington and Marlin rifles, as they are advertised as proof tested.

Having shot hundreds of Lake City arsenal 7.62 NATO M60 proof loads (41 gr. IMR4475, 172-gr FMJBT bullet, 180-gr. case and FA956 primer; 67,500 cup pressure), none had any visible evidence of primer issues. They were hard to distinguish visibly from standard M80 ammo with the same case, powder charge and primer but with a 147-gr. bullet when fired in the same Garand.

 

[Jimro]

For reference,

The SAAMI 223 "commencement of rifling angle" is 3 degrees, 10 minutes, 40 seconds based on the link Brian Pflueger provided. The CIP "commencement of rifling angle" is 3 degrees, 10 minutes, 36 seconds based on a cartridge spec drawing I got ahold of from CIP.

So in an absolute sense the CIP 223 Rem reference chamber is slightly different than the SAAMI reference chamber, but not enough to matter (only 4 seconds angle difference, 1/275th of a degree), which explains why the CIP pressure standard for 223 Rem is higher than the CIP standard for 5.56x45, as the chamber can account for the 4k PSI increase in pressure.

Jimro

 

[JohnKSa]

...it often goes unnoticed...

...even though no symptoms of overpressure are showing up...

These two quotes do not quite say the same thing.

One (mine) says that the mismatch, in isolation, often does not produce overpressure symptoms.

Your statement, says that the mismatch, in isolation, does not produce symptoms. I would not go quite that far because it does appear that the mismatch can sometimes, in the worst case scenario, as it were, produce symptoms, even in isolation.

The context of my comment (that you quoted) was an explanation of why the mismatch did not always seem to produce symptoms--an observation made by several persons, including some of the independent experts. The reason is that the maximum pressure rise quoted as being caused by the mismatch is a maximum, not a minimum or even an average. In the worst case scenario, the data available suggests that the mismatch can cause problems in isolation. But it does not always cause problems in isolation because clearly, not every scenario is a worst case scenario.

...seemed to think that those additional factors might be important, and so do I.

Any factor that contributes to a significant pressure rise over what is expected is important. Since the mismatch can, by all accounts cause a significant pressure rise over expected discharge pressures, it is important. In the worst case, it could even be critical in isolation. If it is combined with another contributing factor then pressures can rise to critical levels even if the mismatch pressure rise alone wouldn't otherwise be catastrophic.

It's an important thing to understand. For example, a person who has been ignoring the mismatch warnings with apparent impunity may discover that if they are put in a situation where another contributing factor (e.g. high temperatures or an unusual amount of fouling in the chamber--factors which would otherwise generally be considered benign) is present, that they may begin experience pressure problems.

At that point a proper awareness of the mismatch and what it can do would be very useful. A person focused on trying to resolve the pressure problems in that particular environment would be confused (for example) as to why high temperatures (which typically result in relatively minor pressure increases) are suddenly apparently causing overpressure events unless they were aware that the mismatch was a potential contributor.

 

[Jimro]

JohnSKa,

I agree, a throat mismatch will lead to higher pressures. From what we've seen that pressure increase is both observable and repeatable, and will increase the odds of some defect in the ammunition causing a pressure spike that pops a primer.

I think, based on ammunition lot testing over chronographs, that a lot of the 5.56 ammo known to pop primers (Winchester Q3131, Fed AE, Guatemalan surplus,) are hotter than actual NATO specifications. I know that the FBI OTM load was specified much hotter than SAAMI or NATO MAP based on their contract specification.

A looser leade can alleviate some of the pressure, but it cannot alleviate all of ammo defects, which is why we see popped primers in 5.56 chambered AR rifles. I think that quite often in the AR the popped primer is due mainly to the powder burning improperly to cause a mistiming of the gas system, or a secondary pressure spike pops the primer back out after the bolt unlocks.

Jimro