I think elk are tough to kill particularly when they are on high alert or already have been shot at. While no doubt a 243 will do the job. I’m not a fan of a dedicated elk rifle that doesn’t start at 300 Win if you need to stop not just kill them.
Once there with good bullets it just doesn’t make enough difference to the elk so it is purely your preference.
The most rabid & knowledgeable public land elk hunter I know shuts his business down a month to hunt 3 states, practices at long range all year. He was using a 30-378 Weatherby and now uses a 7mm STW all personal preference.
