I read all of Peter Capstick's books many years ago, right after they were published. As I recall he also used a shotgun for wounded leopards, but made himself a suit of armor from linoleum tiles wired together to form a breastplate of sorts. He said that a leopard would leap for your head/neck area, grab you with it's front feet and use it's rear feet like buzz saws to rake your chest and abdomen.
Obviously the shotgun was used to prevent that from occurring.
I can't remember for certain what action type he used.
Blue whistlers (buckshot) are serious business at close range, no doubt.