Not true, older guns are an entity into themselves. You must do a chamber cast to determine chamber dimensions.I ran into many issues trying to load my own shells. My chamber was tight and would not accept 8x 57 reformed brass as the base was too big. Also 358 bullets produced sticky bolt lift. Found bore size was 355. Contacted Quality Cartridge for casings (not cheap but correct size) and bought a swaging die to reduce 358 bullets to 355. I have now brought the old girl new life and found the perfect still hunting rifle.9x56 Mannlicher and 9x57 Mauser are virtually identical. If you can find a copy of "Cartridges of the World" it has some data. The .358 Winchester is also a virtual clone of these two cartridges and you can use .358 starting load data and you will be very close to stndard loads for either. The biggest problem will be bullets as the 9x56 uses .356 bullets. Generally you can get away with using .358 bullets if the chamber neck is large enough to do this, and almost certainly it will be.The extra .002 will not make a significant difference in pressure as most seem to think it will.