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Old November 29, 2011, 06:11 PM   #49
Join Date: March 4, 2005
Location: Ohio
Posts: 11,264
My point was just that the M80 is not shorter on both velocity and energy, but only on energy, being spec'd 10 fps faster. This applies only to comparing the FMJ ball loads (M80 vs. M2), of course.

I mentioned the SAAMI pressures not because the military loads to them, but because that affects what velocities you can get to in bolt action rifles. The slightly higher pressure limit in the smaller case makes up a little for its lack of powder capacity if you observe the SAAMI limits. But, as I perhaps should have expressed more explicitly, under its own constraints, the military loads would not benefit from that.

Then we get into the whole mare's nest of the new specs. The military never embraced the practice of referring to copper crusher results as CUP, but continued to call them psi into the mid 1990's at least. This caused a lot of confusion among American handloaders. They've now switched to Piezo transducers so the 50,000 psi number has changed. The 7.62×51 peak pressure used by the NATO allies and the CIP is 415 MPa, which converts to 60,191 psi. The European standards use a pressure barrel with the sampling port nearer the case mouth, and this causes their transducers to report pressures typically a couple thousand psi lower than SAAMI transducers do on most high power rifle cartridges. So the same peak would be reported at about 62,000 psi in SAAMI spec test gear, which is the current SAAMI Piezo spec. Since it is also NATO's spec (after translation), presumably it is also the current U.S. military spec, but I don't have a U.S. military spec sheet.

I also don't know what the military spec for the .30-06 is now, assuming they've updated it. But if it, too, corresponds now to the CIP/NATO specification, then it should land on about 60,500 psi after translation for pressure sampling locations. I don't know that they've done this, but if so, it would mean the peak pressure specs are no longer are the same on the two cartridges.
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