Hello friend. I bought a 338 RUM about a year ago and love it... I use factory ammo and have found that the 250 gr. corelock Ultras work very well on just about any big game animal. they hit hard and shoot flat. I have killed 2 big 500 plus pound Oryx and a nice 6x6 bull Elk. the Elk was at 450 yards out and dropped like a stone. My bullet retained 70% of its weight. On the two Oryx they also fell in their tracks although one was only about 150 yards away. The energy lifted the animal off its feet and tossed it like a rag doll. The good news is that I had very little met loss and the bullets mushroomed very nice. all three retained about 70% of their weight. Hope you like it like I do. happy hunting. Leroy.