How low can you go?

[338RemUltraMag]

I just had some great results at the range with my 30-06 and uber slow powders (H-1000 and Retumbo) now the question is how low can you go on the powder charge and not have a dangerous situation? I was thinking to look at loads for magnum calibers and see the start charges there and figure up the case volume, but I dont think that would be an equal comparison.

I was shooting with 57 gr of each powder and that gave about .010 compression with a seated boolit, without filler how low can I take this charge?

[runfiverun]

I think I would just back it down until I seen it burning dirty, then add a filler to bring it back to the clean side.

[338RemUltraMag]

I just dont want to experience a secondary kaboom and ruin a pre 64 30-06 the load was good, I need to water drop these I think...