The .404 Jeffery isn't alone in this regard.
All the major and even a few minor American factory cartridges have European counterparts as far as "official" dimensions are concerned. The United States has no governmental authority setting "official" dimensions for our cartridges. Our SAAMI (Sporting Arms and Ammunition Manufacturers Institute) is a function of the member manufacturers.
The Europeans have CIP (Commission Internationale Permanente pour l'Epreuve des Armes � Feu Portatives) in Li�ge, Belgium.
SAAMI's cartridge and chamber dimensions are set by the originating company (.260 Remington by Remington, etc) or the American company loading European cartridges, and adopted by SAAMI -- not established originally by any single American authority following rigidly set rules or principles.
As a central authority with stricter rules and principles, CIP establishes standards that often produce dimensions that don't match the American dimensions for the same cartridges. The differences between ours and theirs are usually more obvious (in the numbers) than substantial ("in the flesh").
