Pressures with 3 Dr. Schultze with 1 1/8 oz.
(pressures converted from long tons/sq. inch to psi by Burrards formula)
2 1/2 case with 1/8 turnover 2.13 tons = 6,040 psi
2 1/2 case with 3/8 turnover 3.03 = 9,060 psi
2 3/4 case in 2 1/2 chamber 3.22 = 9,700 psi
3 case in 2 1/2 chamber 3.71 = 11,345 psi
When long cases are used in short chambers, the paper overlaps the cone and causes greater resistance to the passage of the shot and wads. The pressure then goes up considerably, while muzzle velocity and recoil are both increased.
A few comments; First this reflects what Burrard originally said & was the truth as stated. These shells would have all be roll crimped/Turnover. The increase in pressure of the 3/8" turnover above the 1/8" turnover shos the pressure rise from an increased crimp strength. The amount of turnover is not stated on the 2 3/4" shell but as not otherwise stated it can I believe be safely taken as the normal 1/8". This allows the end of the unfired shell to enter the cone of the 2" chamber thus effectively increasing Crimp Strength & even more so on the 3" shell.
What was later proved was that if the normal 2" load was put in a 2 3/4" case & then closed with a Fold/Pie crimp, the loaded shell was essentially the same length as the 2" shell closed with a roll crimp. This allowed adequate room for the crimp to open, un-restricted & pressures were then "Normal". In a normal length cone, the slight overlap of the "Fired" shell was not enough to create an undue restriction. This, of course, does not apply with those stepped or unduly short cones in which the fired shell would actually lap into the bore itself. This was all well reported on my Burrard who incidentally made no claims as to having "Discovered" it. He simply reported on the work which had been done by "Professionals" in the ballistics field.
The two main factors thus were The "Load" had to be compatible for the gun it was intended to be fired in (R'Mans Concern) & the Loaded shell must be shorter than the chamber allowing freedom for the crimp to open normally.
Not really that hard to understand.
