Primer flattening in a high pressure rifle load is entirely out of the scope of this question. When the primer ignites in a rifle cartridge it actually tends to shove the case forward to the extent of its head space. Pressure from the powder after it ignites pushes the case back against the breech reseating the primer. When loading low pressure cast bullet loads in rimless cases the primer thrust can set the shoulder of the case back & the pressure may not be enough to set it back. It is always advisable to keep such cases "ONLY" for further low pressure use & not to reload a full power load as it would have the same effect as excess headspace, "BUT" this is not the question we were discussing here.
"BUT", you spent nearly as much wordage telling me why my example was irrelevant as I did stating it.
The point of the example is to point out the principle that, as keith stated above, the pressure inside the shell/hull acts in ALL directions............... including against the inside of the case head, driving it back against the breech. This reaction is why higher pressures do stress the breech more than lower pressures. The flattening of primers was entirely relevant, and I heartily disagree with your claim that it is not. It
PROVES that the case head is driven rearward with great force into the breech. And that, was why I used it as an example.
I'm done with this one.
A man convinced against his will,
is of the same opinion still.
SRH
