Doc could probably fix you up and he might even do an ACP case since you are already set up for those. Might have to shorten some cases a bit to gain some metal around the fire channel.

ps: does the head of an ACP case even fit inside the opening on a UMag 209 hammer? And I don't know if the standard spring would be enough to keep the case from trying to blow back out at you. And I don't know if there would be room for a standard case to be inserted/removed (doubtful). I think you would be talking major re-design.