I've used nothing but Barnes XBT, and Failsafe bullets on Plains Game, lightest rifle was a 300WM/180, then 338WM, 340Wby , 35 Whelen AI, 375 H&H. But the heaviest game we all killed were zebra. There were lots of Cape Eland on these "farms" ( we would call them ranches) but we never hunted them. Indeed, they are big. I had a missionary friend who lived in SA back in the 90's and early 2000s. I had given him a 30-06 and a bunch of the old Federal High Energy 180 partition loads. They went 2970fps in that rifle! He had no trouble with Cape Eland. His friend did make a wrong first shot on Blue Wildebeast and it took all day and many shots later to get him! So, "if it were me" and I wanted to use that 6.5 SAUM I would use a heavy mono, shoot him at the base of the neck ( where it joins the shoulders) or base of the skull. I once shot a zebra through the head ( 210 xbt form 340Wby) and it did not ruin the cape.
