Just curious why black powder? The 9.3x74 was developed for smokless powder in 1900 and has a slight bottleneck. It was used as a medium bore cartrige in the German African colonies, in much the same way the 375 H&H, 360 Jeffery, and 350 Rigby were, in the British colonies. The 9.3x72 was a black powder cartridge.
for every stereotype there's a prototype