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I saw the calculations once but no longer have the numbers.
Look at a fired case, you can usually see the expansion ring where the brass gripped the chamber... until it didn't. Cross section there, measure and do the geometry to get the actual thickness of brass. Multiply that by the tensile strength and you will get the load necessary to stretch brass back into the headspace. Which I recall is not a lot compared to what is transferred to the locking lugs. The case isn't holding much, it is mostly just a sealing gasket.
The BPCR guys did some work with .45-XXX spitzer shapes a number of years ago. They concluded it did not help much and the present crop of "money bullets" has an ogive calculated to give the best results transsonic.
Of course you can launch them faster with smokeless.
There was an outfit making .458 spitzers but I no longer have the references to find them, if even still in operation.
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