Most modern proof loads for shotguns are a double charge (or very close to it) so if you are wanting to exceed safe levels, you would be, indeed,
I believe current SAAMI proofing standard is something like two shots of 19,000 to 20,000 PSI under an ounce and a half without measurable dimensional changes. Almost 200% pressure. Where did I say ANYONE was shooting "proof" loads? Where did I say shooting proof loads was safe? Do you think shooting proof loads in a shotgun is safe? I would be very surprised if any of the manufacturers have a person hold the gun when proofing them.
SHR970 mentioned proofing his reloads in a shotgun, but I think anyone outside an engineering lecture hall would realize that didn't mean shooting 19,000 PSI loads to prove they were 19,000 PSI. How exactly would that test even show anything at all? If the gun doesn't fail critically you assume they are below the SAAMI proofing load? Anyone with any flexibility in thought would assume he is testing his reload batches in a cheap gun so if he made a mistake or pushed things just a little too far it wouldn't damage his expensive gun, not following SAAMI proofing standards. The reason that should be obvious is he says proofing the loads, not the shotgun.
Does a double charge equal double pressure? It is my understanding it would be an extremely rare coincidental fluke if it did. Pressure is dependent on a number of variables, some of them interrelated, and I don't think changes in ANY of those variables has a linear relationship to pressure. It wouldn't surprise me if some double charges result in triple or greater pressure. That is why a near double pressure load can be used to proof without resulting in any dimensional changes, but a double charge almost always results in catastrophic failure. That is some very basic information.
The high pressure developed by a pistol or a rifle cartridge in an adapter drops wildly as soon as the bullet leaves the "muzzle".
But, what about before it leaves theadapter muzzle? What about bolt thrust? Pressure on the hinge of a break action? There's more than just the chamber walls that has to hold when a cartridge goes off.
You cannot just extrapolate date. If you could all the ammo makers wouldn't have pressure barrels. Incredible.
You sir, are correct. I'm not recommending anyone do it. I'm just saying they do and I have fired a few of the shells. I also don't recommend you drive more than double the speed limit on the highway, although people do, and I have. I'm not telling people to drink until at twice the legal limit, although people do, and I have. They really didn't know the pressure. When I fired them I didn't really know either. I'm not sure I would fire them again. UAs I understand it, unlike with a lot of metallic cartridge reloading, there are no clear warning signs of pressure overload in a shotgun. I was reassured because I knew this gun had been firing the load for decades, and I knew it had been checked for dimensional changes by someone I believed to be a competent gunsmith with some regularity.
It's not like I am talking about 357 ROF here... I'm talking about working up , a published load to max and then pushing it slightly past the published data. Hoping for something of maybe 13,000 PSI(a jump similar to +P for metallic cartridges), but like has been said, you can't extrapolate the data and they don't have pressure barrels, so who knows what level the pressure is really reaching. Likely WELL below a proof load, though. I wouldn't have run them through a pump or semi-auto and was clearly advised not to.
Challenger is the classic "why you can't extrapolate" example pounded into students heads. There were 23 previous data points between 53 and 81 degrees farenheit. They used that data to decide it was safe to launch at 31 degrees. That is just idiocy. Not the same as working up 1/10th a grain at a time.
