The Ackley Improved does sound like a reasonable choice. As the 30-30 headspaces on the rim as mentioned factory rounds can be fired in it & after firing you have fireformed cases for the new chambering. This should not cause any problems down the line. Of course after the initial firing one would not Resize to original 30-30 size.
This of course "IF" the lengthened shoulder will clean up the groove in neck. lso I would not recommend hot loads in the AI case, stick to no more than original pressures, lower would be good. "Supposedly" the lessened body taper will reduce back thrust on firing.
