6K psi = 75% of 8K psi. I don't have any absolutes but would suspect that the primer flowing is up in the area of 60K psi or 750% of the 8K. This is why I said it was irrelevant to the question asked.
As I said in a prior post the question will not truly be answered until someone performs an actual test in which a strain gage is placed across the gap & precise readings taken.
What I am convinced that many are forgetting the shortness of time the pressure is actually applied. All of the examples which are being used would be completely true "IF" a static load was applied. "IF" we plugged the end of the chamber & pumped up pressures of 6K & 8K then the action would be stressed 75% as much with the 6K pressure as the 8K. This is not the case though. Either the 6K or the 8K pressure in the shotshell will not deflect the standing breech of a break open shotgun to the same extent as would this static pressure.
When this breaks through then perhaps it will be recognised what I am saying. working on the premise that the charge will travel down a 30" barrel in about .0003 seconds with the paek pressure occupying no more than about ˝" in the chamber or 1/60th of the total barrel length then assume the time involved at peak pressure is around .00005 seconds. Assume this to be for the 8K load. Then the flatter peak curve of the the 6K load would take around .000066 seconds. What then will be the deflection to the standing breech with 8K being applied for .00005 seconds versus 6K being applied for .000066 seconds. I honestly don't have a definitive answer but my opinion is different than many have.
"IF" you fail to take into consideration that both Force & Time are involved as a static pressure level is not reached you simply have not looked at the entire equation. Things are a lot more involved than just saying that 6K pressure will stress the action only 75% of what 8K would. It might be nice if it were that simple, but its NOT.
