Of course, the 400/350 and the 350 Rigby Magnum are not the same cartridge, although they were built on the same action and used the same style stock. The 400/350 is a rimmed cartridge, much like the 9.3X74R. In fact, it is possible to form 400/350 cases out of 9.3X74R brass.

The original Mauser magnum action with a slanted magazine box was designed specifically for this rimmed cartridge.

The 400/350 featured a long parallel sided round nosed 310 grain bullet of great penetrating power at a modest 2000 fps. The .350 Rigby Magnum used a 225 grain bullet at 2625 fps, clearly designed to compete with the .375 H&H.

I once owned an original Rigby 400/350, but since the 310 grain bullets with which it was originally loaded were no longer available, and no prospect of getting any, I let it go, much to my present chagrin. A few years ago, I had the opportunity to reacquire it, but alas, no longer in its original condition. It had been rebarrelled to .375 H&H (a conversion which Rigby also performed) and restocked, but it still occupies a place of honor in my gun room.

The rifle on sale in Germany is described as follows:

Original RIGBY / ZIVILMAUSER Kal. .400/350 mit Single Square Bridge, mit ORIGINAL MAUSER MAGNUMSYSTEM, nicht nummerngleich, Waffe wurde fachmännisch restauriert, mit gr. Klappkimme, originalschaft, auf dem Lauf sign. "John Rigby.......", linke Systemseite "Waffenfabrik Mauser Oberndorf a./N."Knopf zum Öffnen des Magazindeckels im Abzugsbügel, sog. "SLANTED MAGAZIN BOX" Bj. um 1905, Lauf leicht rauh -eine selten angebotene Safaribüchse

Oringinal Rigby commercial Mauser, 400/350 with single square bridge original Mauser Magnum action, non matching numbers. The weapon has been professionally restored, with original folding sight, on the barrel signed "John Rigby...", on the left side of the action "Waffenfabrik Mauser Oberndorf a/N". Floorplate latch within the trigger guard loop, so called "slanted box magazine" Built around 1905, barrel slightly rough--a seldom offered safari rifle.

The starting price for the auction, 5,400.00 EUR = $7,141.20, seems a bit steep, given the mismatched numbers, the refinished metal and stock and the rough bore, but maybe not.