I've always thought the 7x57 is a pretty good all-around caliber--worked for Bell on jumbos. 7x57R/12ga or 16ga will handle anything if you can shoot, and it's one of the most common configurations for BBF's and cape guns. Mine is the Brno ZH-204; hefty enough to shoot full-deck 7x57 loads, and Brenneke makes a pretty good slug for the 12. I just got a set trigger for it; somebody in Manitoba put one on ebay, and it dropped right in; just two pins. I'd rather have a drilling, but...this'll do.