Its interesting that some PH's use a shotgun on leopard and some do not saying they are useless (maybe not slugs) but reading the comments here and on AR the best firearm to use on wounded leopard would be a FN FAL 7.62mm (or a Lithgow L1A1

)but if not available I would go for a fast lever Winchester .405 or Marlin .444 even a double .470 as these cats are like lighting.