I quoted Mark when he said, in the video, that the breech cap was "the hardest, strongest part in the whole gun" which is clearly the same as saying that the barrel (and every other part on the gun) was not as hard/strong as the breech cap.We don't know that the barrel tenon was or wasn't tempered, or what alloy was used. Mark didn't cover that in any of the videos I've seen.
So we don't need to know what alloy was used for the barrel or how it was heat treated to know that it was not as hard/strong as the breech cap. Besides, even if he hadn't made the statement, the fact that the barrel threads sheared instead of the breech cap threads would be pretty telling evidence of which was harder/stronger.
Sometimes, there could be, I agree. But what I said was very plain and also true. ..."hardening only one side of a threaded connection can't make it any stronger than the threads on the other side of the connection." Is it possible that the barrel tenon was designed so it was just only very slightly less hard/strong than the breech cap? It's a possibility, of course, but I don't see how making up all these possible explanations fits with your repeated assertions about how we shouldn't speculate.Having said that, sometimes there is a good reason to use a softer or weaker material or lower temper on one side of a threaded connection.
We don't need to know the chamber pressure, nor do we need to know if the overpressure was caused by a barrel obstruction to know what happened and to see how the gun failed.Without knowing the chamber pressure that was actually generated and if there was or wasn't a barrel obstruction, it really is all speculation.
1. We know that an overpressure event resulted in three parts of the gun being driven towards the shooter with lethal energy levels. (In spite of the fact that it is pretty clear that this is due to design choices, we could speculate that isn't because of the design but is due to some unknown factors, but I believe your position is that we shouldn't speculate.)
2. We know that the breech design allowed gas to act on an area more than 3x larger than a breech plug design would have. (It's true that we can speculate about whether or not the force applied was really 3x larger due to assumptions we could make about how the gas escaped around the head of the case, but I believe your position is that we shouldn't speculate.)
Why would it? Is there any reason to believe that this failure calls the strength or safety of other firearm designs into question?Which I guess begs the question if any manufacturer does such testing, and should they?
Are you speculating that perhaps he tested to failure but found the failure benign and then further speculating that had he tested with even higher pressures he might have discovered a different failure mode similar to the one that produced this video?Even if he did, I can't imagine having tested loads above the pressure that caused failure because you'd have already established that failure point.
It looks like what you're really saying is that no one but you should speculate, or perhaps that speculation is only acceptable if it makes Serbu look better. Similarly, it also seems that what we know is only what we know if it puts Serbu in a positive light, and everything else we know isn't really what we know.