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Old January 18, 2022, 09:56 PM   #14
Join Date: March 4, 2005
Location: Ohio
Posts: 19,883
Old Roper,

I don't know where you got those numbers, but unfortunately they are not correct. SAAMI says ammunition manufactured to their standards "can be expected to produce velocities within a tolerance of ±90 fps of the tabulated limits." This same velocity number is given in all the standards, so it applies to rimfire, shotgun, centerfire rifle, and centerfire handgun cartridges.

Pressure tolerances vary with peak pressure. It is a range of pressures and not a plus and minus tolerance. That is, it is the span or extreme spread of pressures that is limited, but the middle of the range does not have to be centered on the average value. The range is called the Maximum Extreme Variation (MEV) and for statistical reasons is equal to 5.16 times the standard deviation of the pressure. The maximum extreme spread is therefore determined by the SAAMI standard's Maximum Average Pressure (MAP) and it's standard deviation (SD) limit. For centerfire rifle, that limit is 4%, and 5.16 times 4% is an allowed pressure variation range of 20.64% of the MAP. This is rounded down to the nearest 100 units of measure. So if you load a 30-06 to the SAAMI Maximum Average Pressurized vale of 60,000 psi or 50,000 CUP, the maximum variations, after rounding, will be spans of 12,300 psi, or 10,300 CUP.

For centerfire handgun the standard deviation limit is 5%. For shotgun shells it is 7.5%. For rimfire SD is limited to 4%, like centerfire rifle.
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