When the crusher system was first placed into use the pressures were recorded as PSI as seen in old data. At this point in time they did not have the means of reliably calculating true PSI. When the PE system began to be used which recorded true PSI it was realized a distinction had to be made between the different systems so PE pressure took on the use of PSI & the others became either LUP or CUP depending upon the mat'l used for the crusher. There are several factors which affect the reading of the crusher measurements which ate not consistent from load to load so there is no absolute conversion from one to the other. The British did however by recording crusher pressures & PE pressures simultaneously work out a formula which would give close results for their crusher pressures compared to PE pressures. This formula was 1˝ times crusher pressure in tons, minus ˝ ton = PE tons. Thus (3 x 1.5) - .5 = 4. As the British ton was the long ton of 2240 lbs then 3 tons (6720lbs) crusher pressure became 4 tons (8960lbs) PSI. This formula was good only within the limited range of LUP's normally encountered in measuring pressures of shotshells & no attempt should be made to use it for CUP as used for the higher pressures of rifles.
