The .405, like the .444 Marlin, was made for use in lever action rifles. That required restricting both powder capacity and bullet weight. With a double rifle you can use cartridges that do not have those limitations. In medium bore, the 9.3x74R is one. The 375 Flanged is another. I don't have the talent required to build such a rifle but if I did I would choose the 375. Have you considered that cartridge?

"Although slimmer and less muscular
than its English brethren, the 9.3x74R (left)
is recognizably from the same era as the
.375 Flanged (center) and .375 H&H." - African Sporting Gazette

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