I don't know that I buy into Burrard's formula.
I was looking at data for International the other day, and Hodgdon still publishes pressures using both systems in the same chart.
Apparently, they are unable to convert and don't want to re-shoot old loads just to get PSI.
Interesting that they can assure SAAMI standards with loads published in LUP.
Comparing very, very similar loads within .1 grain of charge and with primers considered by most to be so similar as to be interchangeable, the difference is indeed 'in the area' of 15%.
I don't find anything approaching 33%.
