It is built on a SSB Mauser action, which is the same length as my Rigby slant magazine .375 H&H Magnum and accepts H&H Magnum cartridges in the magazine.
Cabelas says that it was originally a .375 H&H which was rebarrelled to .404, and the ad originally attributed it to Jerry Fisher (Fischer, as they spelled it). Jerry says not his, maybe Al Biesen. I thought Griffin and Howe, but Paul Chapman of G&H says no. It's a beauty, in any case.