Different organizations use different pressure testing methods, which results in different numbers describing the same event.

According to Wikipedia, NATO specs the 5.56 at 62,366 PSI.

NATO pressure specification

According to another source, NATO does its pressure measurements at the mouth of the cartridge, as CIP does in Europe. This results in a pressure reading different from our SAAMI method.

NATO method

SAAMI specs the 223 at 52,000 CUP and at 55,000 PSI.

All these pressure measurement methods, plus the CIP crusher specs, are readily converted to one another.

I don't have data to create a conversion for NATO specs, but if you want to compare CIP and SAAMI pressure numbers for rifle cartridges, then, to a good approximation:

CIP PSI = 18,419 + .695* SAAMI PSI

CIP CUP = 2428 + .825 * CIP PSI (very precise fit)

CIP PSI = 4772 + 1.067 * SAAMI CUP

This last result is extremely curious. For all practical purposes, CIP PSI is numerically the same as SAAMI CUP, offset by an amount equal to the strength of the brass case.

If you want to assume that NATO is using the CIP method (maybe, maybe not), then 62,366 NATO PSI would be very close to 54,000 SAAMI CUP, vs. the SAAMI 223 spec of 52,000.

Last edited by denton; 12/12/08.
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