Note; that many, many years ago Burrard stated that pressure bbls in England had been fitted with both crusher & PE measuring equipment so the pressure could be measured simultaneously by both methods. Within the range of shotgun pressures a workable conversion was arrived at. While not exact it was considered to be "Close Enough" for all practable purposes.
The formula was 1˝ crusher tons - ˝ = PE tons. Realizing the British ton is the Long ton or 2240lbs then this comes out as follows for PSI;
3x1˝ - ˝ = 4PE tons
4tons x 2240 = 8960PSI.
Notice this is only 22 PSI different from the figure Drew gave us, certainly within workable range.
The 3Ľ ton pressure of a 2 3/4" chambered British gun would by this same formulla convert to 9,800 PSI
Inso far as I know this formula is applicable "ONLY" for British crusher pressures.
