You might try a lighter bullet too. Say a 124gr. The velocity and energy go through the roof. Marlin used to claim a 22% increase in velocity and a 50% increase in energy over the same round fired in a 4" barrel. Basically it becomes equal to a factory loaded .357 Magnum without the recoil or loud noise. I know that the 147 gr slugs lessen this effect. No such claim was made for the 45 version. Perhaps the 230 gr slug might have had something to do with that.
Thanks for posting. Keep us informed.