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Anyway, I was looking at a new reloading manual, (actually a Hodgdon update magazine) and I was comparing the 223WSSM, 22-250 and 220 Swift. One thing I noticed was the pressure differences on the high side between the three. The WSSM's have some huge pressures...
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Actually, they all operate at very similar pressures. The difference is the measurement systems used. The "old" system when the .22-250 and .220 were introduced was a mechanical crusher system measuring in CUP, or Copper Units of Pressure. In the past decade or more, electronic measurements have become standard, and the WSSM cartridges are measured in psi.
Example: the current SAAMI standard for the .22-250 is 65,000 psi, virtually the same as the WWSMs. It is nominally the same "pressure" or contained force as with the old CUP value.