BRNO's are apparently good actions for conversions.

What pressure levels you want to load to, are also important in this discussion as they may open or close opportunities for certain actions to be used.

Factory loads usually run under 22,000psi/cup.

Hodgdon and Lee say that even trapdoor springfields can be loaded to 28,000psi/cup.

At 28,000psi, with selected powders, you can achieve over 2,100fps with 300gr., over 1,900fps with 350gr. and over 1,800fps with 400gr. bullets.