I picked up a very nice custom 98 Manuser at the gun show today that is marked on the barrel ".404 Express". RCBS made dies for it from the chamber cast and called them "404 B.J. Express".
I've found only a few references to it - it appears to use a .411 diam. bullet in front of a .375 H&H case blown out and necked up to .404. As such it should have more punch than the .416 Taylor and approach a .416 Remington powerwise.
Anybody ever hear of this caliber before or have any experience with it? I've got to slug the bore and find some bullets for it.