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I know each cartridge has been assigned a maximum pressure, but what goes into that determination? A model 70 Winchester in 30-06 has a max pressure of around 54000psi while a 300 WSM in the same gun has a max of around 63000. Why the difference?
 

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As near as I can tell, SAAMI specs are worked out between the regulatory body and the company submitting the round for standardization. Seems to me the strength of the firearm that will be chambered for the round, as well as the dimensions and strength of the brass, are taken into consideration when determining how much pressure to list the round at.

I will not encourage anyone to do so, regardless of the firearm used, but the various '06 offspring operate at much higher pressures and I've known more than a few people to spice up the old warhorse, in a strong bolt action. Rounds such as the 44/40 and 45/70 have two or three different "levels" of reloading, to accommodate the strength of the action/firearm they're being shot from. In the case of the '06, I will go so far as to say the early bolt-action rifles it was chambered in determined why the pressure was held relatively low.

Edit: The pressure rating of a given cartridge is NOT defined strictly by the thickness or strength of the brass, alone.
 

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From what I understand, it is the brass. Remember how we used to say this about audio systems. What good was it to have a thousand dollar turntable if you had a 3 dollar needle. The brass is the weekest link in the system. It almost always will be. Most factory stuff has to be loaded to accommodate all the firearms out there. As we move more into the future and companies get braver we may see pressure tolerances increase. They will never increas higher than the ability of the brass.
 

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The 30-06 has been around since, you guessed it, 1906. Consider how many different makes and models of rifles the 30-06 has been chambered in, in the last 100+ years. Not all of those rifles are as strong as a modern bolt action.
The 300 WSM hasn't been chambered in old rifles, since it's a relatively new cartridge. So, makers of 300 WSM ammo can be sure the rifle their ammo is used in is solid.
Not so with the 30-06, therefore the lower pressure limit.
 

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Likewise, the 44/40 specs from SAAMI restrict it to 16,000psi, so that it is safe in '73 rifles and a bunch of different revolvers it has been chambered in. When fired from a model '92, or a knock-off, the same cartridge can be very safely loaded to much greater pressure, as evidenced by the fact that Winchester used to load "WCF" rounds for the 44/40 at nearly twice the SAAMI spec.

Maybe with the newest cartridges brass is the limitation, but with a lot of our older cartridges, the strength of the action, steel and other metallurgy was taken into account when establishing pressure limits. To a certain extent, I think it's fair to say pressures were kept down "just to be safe", considering how imprecise their tools for measuring said pressure used to be! Say what you will about modern cartridges, but the science has moved forward a great deal in the last 100 years, such that there is a greater understanding, if not greater actual performance. ;)
 

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read bear trackers post as it preety well sums it up.--rifles are like chainsaws. why try and scream the tits out of them. load and tune moderately, and if you need more power,get a bigger gun.--just my take.--ps -have been guilty of trying to wring out the last drop of grunt.-i soon woke up.- as we all do.
 

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Also if the new short mags were not loaded to that 63,000+ psi then they would not be the new miracle cartridges they are touted to be.;)
 
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