CAUTION: Do not use anything relative to the 45-70Gov't for the 450Marlin or the 458X2". The 45-70 is a much lower pressure chambering than the other two.
The 450Marlin and the 458X2" are about the same as far as pressures and velocities go. Remember,the 458X2" has been around waaaaaay longer than the 450Marlin.
Also consider the strength of the actions that you will be shooting these chamberings in. ---- SAWMAN