I've been using 00Buck and I'm thinking this is the right load for a cylinder bore shotgun (all of my shots are within 40yards)
#4 buck is generally
regarded as the best by most experienced predator hunters, although the Dead Coyote load with T-shot is popular but expensive. The 3 inch #4 buck loads carry 41 pellets and are less expensive. Your range depends on your pattern, but a cylinder bore is probably going to shorten your range. Either of the above loads is going to pattern better than the standard 9 pellet 00buck load. Some folks have good luck with lead BB loads as well. Good luck, and go knowck some dogs down!