I figure things this way as to the "Garand Dafe" ammunition. While the phrade has been floated around for decades for the newer Garand enthusiast who have a CMP or DCM rifle the SMP recently included this in the pamphlets that ship with their rifles:
So as many consider the CMP to be the leading authority on the M1 Garand service rifle and consider the CMP as the former mentioned experts they are going to accept that as gospel. This argument has persisted for decades and will continue for decades regardless of how you or I choose to explain it. One of those “Nobody’s right if everybody’s wrong.” Buffalo Springfield’s lyrics are just as correct now as then.
Moving along to chamber pressure in any rifle. We have come along way in pressure measurement especially with new pressure sensors and yes, there is no mathematical correlation between CUP (Copper Units of Pressure) and actual PSI (Pounds Square Inch). Matter of fact years ago in this forum one member posted an actual formula they had derived but it really never worked out.
A big part of the problem is the older CUP method for measuring pressure verse the newer piezo method are not the same. Measuring pressure involved a defined method. Now told in the CIP method and even the CIP numbers won't agree with the SAMMI numbers. All of these methods are well covered in how it's done. When measurements are not taken using the same procedure they will obviously give different results.
In conclusion rather than argue a point where there are no winners and nobody is about to change their views let sleeping dogs lie. This forum and just about every gun forum out there in the Internet world has endless pages of this same argument.
Uh Oh, big warning here.
Just My Take....
Ron