You're absolutely right... and your diagram exactly proves the point that I've been making all along. Headspace and case head protrusion are entirely different and unrelated.
I am beginning to see that any further discussion will be fruitless as what I see is a severe group think based on what I will call Strong Pressure Vessel Delusion or SPVD. The human mind is always trying to make sense of the world, people cobble together a view of how the world works based on their experiences, their intuition, and what trusted authorities tell them. Frequently the theories that come out make sense logically, legalistically, but are actually physically impossible. We argue all the time about how the universe works, and this thread is just another example of how different foundation theories, stated or otherwise, result in confusion and conflict.
I think someone suffering Strong Pressure Vessel Delusion perceives the world something like this:
It just makes sense that the cartridge case is strong: the weakest portion of a 308 case bursts just at 650 psia, the heaviest probably above 40Kpsia. From what I have read the strongest human jaw can create a bite force of 256 psia, while the Nile Crocodile can create a bite force of 5000 psia! So given that you cannot crush a case in your hand or pierce it with your teeth, your brain understands that a cartridge case is very strong. Being strong, the cartridge case can do the job, unsupported, like all the other pressure vessels you have ever seen or experienced. You have reasoned while firearms have chambers, they are not really necessary. You could, with duct tape or clamps, fasten the case down, hold the case mouth up in the bore, to form a gas seal, and all it takes is primer ignition and gas will vent out blowing the bullet up the barrel. In a way similiar to the many times you have used a compressed air tank to clear debri. Compressed air tanks are plenty strong, they don’t need to be inside something to work, they just need to be on something to work. In an analogous mode the chamber is there simply for precise alignment of the bullet to the bore, which is why we have all these discussions about neck sizing or partial neck sizing: these are simply ways to best utilize the precise launching axis that a chamber provides. The wise posters in these threads reinforce your concepts of SPVD. Ideas of case head support are baffling and inexplicable: it does not matter how much the case sticks out of the chamber. Case head protrusion has nothing to do with nothing and is related to nothing. As you have noticed, all firearms are different, case head protrusion is all different, this supports your view that the case does not need support, it is strong enough on its own to handle any and all combustion pressures. This is all very obvious. Cases are strong, so are compressed air tanks, fire extinguishers, and CO2 cartridges. All of them strong pressure vessels. While you do understand that headspace is a measure between base and shoulder, and you have found that too much space between case shoulder and chamber shoulder will cause a case separation, the fact that case head separations occur do not alter your view that a cartridge case is a strong pressure vessel: you don’t ponder this, or it is just one of those exceptions that prove the rule. Barrels are heavy and chambers are thick just for the weight and the subsequent recoil reduction that provides. In fact, you have concluded that the locking mechanism is just there to keep the cartridge in place and by itself does not need to be very strong. Given sufficient friction between case and chamber you could discard the locking mechanism entirely because the case would stay locked in place. You notice that drag racers use wide tires. From this you have deduced that the larger the case, the more gripping area. The more gripping area the more friction there must be between case and chamber. Thus it is theoretically possible to make a case so large that a locking mechanism is not needed. Unfortunately there is never enough friction and the locking mechanism has to be there to prevent the case from floating off into the air like a carnival balloon or a bottle rocket.
I believe the case is a gas seal: that is it is very weak, has to be supported or it will burst under combustion pressures . Since we are approaching this issue from two diametrically opposed views of the universe, I feel that nothing I say will alter your view of the universe. And really, nothing you are going to say is going to alter, by much, mine.
