well, don't find my 1927 georg roth catalog just now
there it is, iirc, the 11,6x82R 450

this is the german-austrian version of the 450 3 1/4 BPE

the case follow the measurments of the older 450 BPE with coiled case http://old.municion.org/450/450Boxer.htm

there you see it the conical base with a long cylindrical body follow this old cartridge

in the 1908 RWS catalog this kind of express cases are called german design

they offer also the express cases "after Eley-London" which have the measurments you find on modern brass.

I fear you need a special sizing die