500/465 ne

I have two 500/465 NE cases.The first one is a fired case made by Kynoch and the other is a new case made by A-Square.The american case has a shorter body and a longer neck than the english one ( the shoulder on the a-square case finishes where the shoulder on the british case starts)
Do you know if the american case is a sort of “basic” brass that has to be formed to match standard cartridge dimensional data before loading?