From 55k to 70k is still less than a proof load and not enough to pop primers.
Assuming that we accept that a 15Kpsi pressure increase won't pop primers, that's a reasonable point in terms of explaining why the primers pop. But it's absolutely not justification for ignoring the mismatch warnings. 70K is within 3% of being a proof load for the .223, and it's obviously well over SAAMI max for the caliber.
Furthermore, if you add in another factor (such as warm weather), then you do get to the point where the two factors, together, can provide exactly the reported result.
Patrick Sweeney's article says that most of the "5.56 ammo you buy isn't really 5.56 ammo."
Again, that's an interesting point, but it doesn't speak to the real issue. That is more evidence as to why it's not common for people to see a problem with this issue. We already know that not all .223 guns have .223 chambers. Now we find that not all 5.56 ammo is really 5.56 ammo.
But that doesn't change the fact that when you DO end up with REAL 5.56 ammo and a REAL .223 chamber, the mismatch can drive pressures up well above SAAMI max. And that it can, under certain circumstances result in blown primers and potentially other issues.
So do we tell people that they should ignore the warnings because they might not have a real .223 chamber or might not have real 5.56 ammo? Unless we can tell them how to know for sure what kind of chamber and ammo they have, it would be irresponsible to make such a recommendation.
The only people providing actual pressure data have already been listed on this thread.
Given that I listed sources like Winchester, Hornady, and SAAMI, that assertion is not remotely credible. Clearly ammunition makers and ammunition standards organizations have access to "actual pressure data".
Even if you want to dismiss all the other sources, I don't see how you're going to be able to make the case that Winchester and Hornady are simply relying on other experts when they provide the mismatch warning.
Secondly, there is a lot of "this could happen" type reasoning going on which leads me to believe that we don't know exactly what is going on.
Even your primary source (luckygunner) doesn't advise ignoring the mismatch warning, stating that his advice is to buy whatever chamber fits your needs and then avoid the mismatch. He also provides pressure data showing that some of his 5.56 testing in .223 chambers showed pressures over SAAMI max.
Maybe we don't know EXACTLY what's going on, but the basics (i.e. the mismatch can cause overpressure discharges) don't seem to be in dispute.
Here are the results. On the left is Lake City 855 fired from the Bushmaster. On the Right is the same ammunition fired from a Colt 601.
A few minutes with a 5.56 chamber reamer and no more blown primers.
So, trigger643, how can you explain the fact that reaming the chamber to 5.56 dimensions eliminated the secondary pressure spike?
(Ok, I kid.)
Thanks for posting your results.
Chamber/Ammo Mismatch=blown primers
Eliminate the mismatch by reaming the chamber and then retest using the same ammunition and firearms=no blown primers.
That
should be conclusive.
i've never heard of a popped primer when firing factory .223 or 5.56mm ammo in a bolt action rifle.
I have heard of a few instances where shooters reported difficulty opening the bolt after shooting 5.56 in a .223 bolt rifle.
The vast majority of popped primers happen with AR-15 rifles.
Which is a good reason to discount the secondary pressure spike as a mechanism given that it is not supposed to occur in barrels of 20" or shorter.
If you are convinced it's dangerous, simply do not shoot 5.56mm ammo in .223 chambers.
The issue here is making sure that others who haven't already made up their mind can get a clear view of the big picture so they have a chance of making an educated decision.
