[Jimro]

JohnSKa,

That's why I keep asking what credible evidence you have (and pointing out that none has so far been provided) to call their conclusions into question.

Please list those conclusions, because the only conclusion ever given is "using 5.56 in a 223 chamber can cause a dangerous pressure spike." Please tell me where in the firing cycle the pressure occurs. Tell me the timing of when the primer is ejected. Please don't say, "Well a mismatch causes increased pressures that lead to popped primers" because that doesn't answer the mail about what I want to know. We've already agreed that using 5.56 ammo in a 223 chamber can lead to increased pressures which will pop primers, but we don't know WHEN that happens, primary or secondary pressure spike, or whether an ignition delay is a culprit.

This is the conclusion you have. You don't have conclusions plural.

The mismatch pushes the pressures up near the threshold limit for problems, and if you get one round that's a little hotter than rest, or slightly oversized compared to the rest, or has the bullet seated out just a tiny bit farther than the rest, or one that hits the chamber when the barrel/chamber temp is hotter than it was for the previous rounds, that one pops a primer while the others don't.

But I think I'm getting through to you because you also wrote:

Why must there be one single explanation for all the incidents of popped primers? There's no logical reason to impose that criteria. I don't see anyone trying to claim that every popped primer in an AR is due to a chamber mismatch. There could be any number of reasons that might cause a primer to pop in any particular gun or with any particular ammo, and none those reasons would invalidate a claim that the mismatch could be one additional cause

.

Which is good because every claim so far about a popped primer in a 223/5.56 gun has been blamed on an ammo/chamber mismatch.

I'm not saying a mismatch doesn't exist, I'm trying to figure out where in the firing cycle that pressure takes place. I believe that if it were a mainly a chamber issue we would see it on the primary pressure peak, and popping primers would be much more consistent.

The reason why pressure trace data is important is that it shows WHERE the pressure happens in the cycle. If it happens on the first peak (the peak that industry normally measures and then stops) then clearly we can blame it on a chamber mismatch. If it happens on the second peak (the only data we've been able to get from that is from the lucky gunner article and shootingsoftware.com) then the bullet is already far down the bore or beyond the muzzle (as in the case of the 7mm STW trace at shootingsoftware.com) when a secondary pressure spike hits, then it ISN'T THE CHAMBER.

I've already written how a more generous chamber could minimize pressure issues due to ignition delay.

The comments by Sweeney regarding his experience with the mismatch strongly support the idea that the pressure rises aren't super-dramatic. He states that he doesn't usually see issues unless there is another contributing factor--such as high ambient temperatures. That sounds like exactly the scenario I laid out in the paragraph above. The mismatch pushes the pressures up near the threshold limit for problems, and if you get one round that's a little hotter than rest, or slightly oversized compared to the rest, or has the bullet seated out just a tiny bit farther than the rest, or one that hits the chamber when the barrel/chamber temp is hotter than it was for the previous rounds, that one pops a primer while the others don't.

And once again, we are back to the condition of the ammunition, and not necessarily the chamber. As you can get popped primers in a 5.56 chamber too, when there are "additional factors" applied.

I totally agree with you that using 5.56 ammo in 223 chambers will lead to higher pressures. From the data available, and expert testimony by Patrick Sweeney, the main pressure event under normal conditions is not dramatic due to a mismatch.

So what I am very interested in is in finding out where in the firing cycle that popping a primer happens. If it was in the first pressure peak I would expect a flattened primer as the bolt is still locked, or if a burst primer I would expect case head expansion measurable by a micrometer. If it happens during a secondary pressure spike and the bolt is unlocked, I would expect the primer to get blown out without any case head expansion, even if the secondary pressure spike doesn't go above SAAMI or CIP pressure maxes.

And that is why having access to data would help me understand where the bullet is when the primer is popped. That is something that the experts haven't told us, or possibly even looked at.

Now I want to build an AR with a gas system that I can turn off with a SAAMI minspec chamber, and run some 5.56 loads through it with that gas turned on and off to see if I can duplicate popped primers with the gas on, and not with the gas off.

And lastly,

Yes I can. If the pressure increase puts the peak pressure right at, or very near the limit for popped primers, then the pressure variations from one shot to the next that are evident in any pressure curve data could easily result in popped primers some shots (or maybe even only once out of a number of shots) but not every shot.

Is a statement directly invalidated by you quoting Sweeney who noted that the increases were not dramatic, and NONE of the actuall numbers of pressure increase (claims of 70 to 77k) are responsible for out crimped in primers, although the only data we have access to shows a much less dramatic increase (from the SAAMI spec to the CIP spec when using 5.56 in a 223 chamber).

That data that shows only a modest increase in the primary pressure spike indicates that it is a secondary pressure concern, or possibly a delayed ignition issue that we didn't see in the data we have available.

But, to agree again, yes using 5.56 in a 223 chamber will show a pressure increase. But I can't answer the questions, understanding the mechanisms of failure, without access to actual data, not just "conclusions" which is why I'm talking data and not "conclusion."

Jimro