I've been on vacation, and had time to think about this.
A single shot action, like an H&R with a .223 barrel, and a 7/16OD .251 liner which can be had for $6/inch puts me in the 25ACP alternative really easy. Slight mod with an extractor. but after that, its all head space and chambering.
If I want to get cute, a Remington No 4 with the Potterfield firing pin mod will do as well.
