Hi Max,
I would not over think it, a DR is still a rifle, just two single shots SxS…..

Match cast bullet weight with whatever weight jacketed bullet regulates, and if you use proper alloy, a gas check, and premium lube then the bullets WILL stand up to standard velocities like the 9.3x74R. You will still have to experiment with the rifle and bullets preferred powder……
I have a 9.3x74, and a famous name vintage London .470, that shoot cast just as well as standard level factory loads.

- Mike