I'll preface this with saying I've never killed an elk, but I've killed a pile of deer, and many of them with a .243 Win and 100 gr. Partitions. From virtually any angle I KNOW that Partition will penetrate the vitals, I've had more than a couple that were severe quartering towards and either had exits on the opposite ham or bullets on the skin on the off-side ham. I wouldn't hesitate to take the .243 after elk with 100 gr. Partitions, or I suppose a Barnes would work as well. That being said, the last few years I've been breaking in a couple of .260 Remingtons. I'd stoke that thing with 140 gr. Partitions and feel even more confident with slightly more recoil than the .243. The .243 will get it done if you need it to.
