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Old January 15, 2012, 12:56 PM   #45
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Join Date: November 8, 2007
Posts: 2,001

One more time and then you can have the last word.

The troubles with trying to make an equation to convert CUP to psi is IRRELEVANT to my point and the evidence supporting it.

The data that produced CUP results at the 46,000 CUP SAAMI limit CLEARLY showes higher powder charge weights than the data that showes psi results at the 35,000 psi SAAMI limit. So, whatever the REAL peak pressures are, they are lower when meeting the psi limit than when meeting the CUP limit with the same powder.

The companies that actually operate both types of pressure measurement systems understand that. I have never heard any of THEM say that they actually measured the same load with both systems and found that that the .357 ammo that reached the psi limit was as powerful as the ammo that reached the CUP limit. In fact, some have said that they shot their NEW .357 Magnum data with the CUP system, DESPITE having the psi system available to use. Usually, that is powder vendors who do that, and the reason is left unstated, but obvious: if they use the psi system, their powders will appear less powerful than the powders of their competitors who choose to use the CUP system, and that would be bad for business. Also note that this means that not all CUP data is "old" data.

Saying "it ain't so" and using the variations in the pressure measurements, powder lot burn rates, etc. etc. to muddy the waters for makng comparisons may delude some, but most of us that have followed this for years are not confused by those arguments. And, I think that I have said enough that the other readers of this forum can make up their own minds.

As for the Handguns Magazine article, I did not read it, so I am not going to comment on its adequacy to make its point. I may try to find it later.

I will however point out that the industry has a habit of introducing new cartridges, adopting standards that make them look fantastic, loading some ammo to that level, then downloadng the commercial ammo later. One of the recent examples of that practice is the .454 Casull, which was given a 65,000 psi peak pressure spec by SAAMI, but for which commercial loads are usually restricted to 55,000 psi to avoid any problems.

I fully expect that S&W did the same with the .357 Magnum all those years ago.

But, that doesn't mean that they designed guns that would be unsafe with the ammo that reached the limit. The guns are supposed to be proofed with rounds that are 30% above the SAAMI limit, not 30% above whatever the ammo companies are currently loading below that limit. So, I still think that ammo that complies with the CUP limit is SAFE enough in modern guns that you are not going to hurt yourself by using it. And, I think that is SAAMI's position as well, since they still have the CUP standard as well as the psi standard. I think that puts me in good company as far as safety issues are concerned.

As for handloading to the CUP limit instead of the psi limit, it obviously needs to be done with care, and that is why I included some cautions. Many of the start loads under the CUP system are max loads under the psi system with this cartridge. So, if the psi system loads have left some people complacent with approaching max, they need to get a new perspective when using CUP data for the .357 Magnum.

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