The jacket on the 338 SST is thicker than the .30 cals but I don't think it would be my choice for eland either but they do kill moose very dead. Zebra/kudu/gemsbok I wouldn't hesitate. I can run 100+ GMX down the barrel of my 338 without any noticeable loss in accuracy but every gun is different but I can't see it tightening up 2.5 inches. I'm guessing higher velocities and your rifle don't get along. My Kimber was the same. In the end I had to go to 225 bullets. Each beast is unique. I'm just happy my current 338 likes the 185s but it's a bit short and fast for many of the standard twists in 338s.