I believe the single biggest factor in what one should have in his hands if following up a wounded leopard is ‘Which gun are you most proficient with under pressure?’ For me individually, that’d make it a 2 3/4” Beretta autoloading shotgun in 12 gauge. While I’ve shot rifles my entire life, I’ve fired shotguns many tens of thousands of times. I‘d want something that I know with certainty I‘d be able hit a fast moving target the first shot and make quick follow-up shots. I believe a load of TSS in T shot driven at 1,350 or so would be devastating on a leopard, especially with multiple shots delivered, which very few shooters could do with even a double rifle.
When I hunted lion and leopard long ago in Botswana, I brought along my Beretta A302, which is a 2 3/4” 12 gauge sporting a 26” improved cylinder barrel. My rationale was that since I’d fired that gun thousands of times at birds, hitting something moving fast would be instinctive and I could deliver 4 shots in rapid succession just by pulling the trigger. I don’t practice shooting my scoped rifles at fast moving targets and working the bolt to quickly fire additional shots in just a few seconds, nor does anyone else. But I’ve shot that old Beretta approximately 30,000 times since the early 1980’s at birds and I’ll argue that, other than the adrenaline and pucker factor, shooting a fast moving leopard would be a lot like shooting quail. Quick reaction, point and pull the trigger. And keep pulling it as fast as possible.
I expect that 1 1/4 oz (that’s 546 grains) of TSS T shot would spread a bit as it penetrated and it’d penetrate very deeply. With an entry hole measuring nearly .75” and a weight exceeding typical .458 caliber bullets, I don’t think a lack of hydrostatic shock would be an issue.
In closing, I have an acquaintance who shot a mountain lion while turkey hunting, at a distance of about 20 feet, in the front of the chest. The mountain lion was about 130 pounds, similar to that of a typical leopard. He was shooting #6 size lead shot. When I asked the guy who shot the lion how effective the shot was, he told me the cat simply crumpled in a heap at the shot. The game warden who investigated the incident (we do not have a lion season in California despite the highest lion population in USA) is a friend and he told me that since the wad was over 6” deep in the chest, it was clearly self defense. Think about TSS in T or 4 buck and how deep it’d penetrate if the wad goes in 6”.
While I hope to never follow a wounded leopard, if I had to, I know what I’d have in my hands if given a choice, and it wouldn’t be a bolt action rifle of any caliber. It’d be the gun I shoot instinctively and have shot many thousands of fast moving targets with.