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is SUPPOSED to be taken in a SAAMI spec test barrel. Those barrels are made to much tighter specifications than factory guns, with minimum specs where they will create the most pressure. When these barrels wear beyond certain values, they are supposed to be retired. This is the barrel that sets the CHARGE weights, and one would think that there SHOLD be minimal differences in the results from lab-to-lab, since that was the INTENT of the testing protocol.

The VELOCTIY measurements are a DIFFERENT story. Because the SAAMI-spec'ed test barrels tend to produce higher pressures AND VELOCITIES than the commercially available guns, the manual publishers typically ALSO test their published loads in a typical gun chambered for the cartridge to give the relaoder a more REALISTIC idea of what velocities he is likely to achieve with the published loads.

So, the pressure is actually from one gun and the velocity is usually from a different gun. Shooting the same loads in several commercially available guns will demonstrate that there is a LARGE variation in velocities from them. THAT is a large part of the explaination of the velocity differences for similar loads from manual-to-manual. BUT, it doesn't have a thing to do with the CHARGE WEIGHT differences, which are SUPPOSED to be coming from as nearly identical tests as possible.

There are a lot of differences in things like powder lot variations, primer brands, case capacties, bullet designs, etc. that DO affect the pressure tests differently in different manuals. More than a 10% variation is unlikely from those factors, so that is why most start charges are reduced 10% below the max loads.

But, SAAMI has also changed the pressure standards and even the measurement protocols several times. Some of those changes are due to "new information" that comes from being able to observe the whole pressure curve (PSI) instead of just the effects of the peak on a copper cylinder (CUP). Especially in revolvers, it was found that the pressure curve looks much different than in a test barrel chambered for the same cartridge. And, in rifles, secondary pressure peaks sometimes appear when power burning rates are not really suitable for the cartridge. So, loading data has been adjusted to reflect such new knowledge.

BUT, new knowledge does NOT explain all the changes that SAAMI has made in pressure standards. The .357 and .44 Magnum cartridges have CLEARLY been down-rated in the transition from CUP to PSI. "Reasons" given by the various gurus don't really stand-up to factual discussion. It has gotten so bad that it is obvious that SAAMI should have adopted a "+P" designation for those cartridges in the PSI standard that is similar to the old CUP standard. But, they have consistently failed to do that, although they have allowed the old CUP measurement process and standard to continue in use. That is why we consistently see new data for these cartridges in CUP in some new manuals.

SAAMI is an INDUSTRY group, not a government regulator, so the standards they produce have some influence from commercial considerastions as well as safety. I suspect that there is a large push to make newer cartridges seem more desirable than the old ones, so that we will rush out and buy new guns, loading tools, etc, and make them bigger profits. Some of the new revolver cartridges were standardized at pressure levels that are just too high for long brass and even gun life. So, why not let the old cartidges CONTINUE to have the same "luxury" of loads that are going to beat-up guns and brass if used continuously? Especially now that SAAMI has the "+P" designations in the new PSI standard?

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