I have taken and been in on the taking of around 100 elk. I have seen them shot with everything from a 243 Win to a 375 H&H. I personally consider the 243 to be too light but it did work on some cows. But, I have never seen it used on a mature bull which is a completely different animal than a cow, and the guy that used the 243 was a local rancher. He could wait for the perfect shot and knew where to place that little 100 gr bullet. In my mind I'd say the 6.5x55 Swede and 270 Win are the lightest that I'd suggest. Never seen one shot with any other 6.5 than the Swede which is why I mention it but I'd imagine any of the new 6.5s would be as effective.
For me I like a happy medium in elk since they come in lots of different sizes and shots can be at any range. 7mm Mag is my favorite round and the one I have used the most.
Well there is always lively discussion on the Fire! My personal biases pretty much mirrors the above. There is a difference between bulls and cows and 6mm is on the light side for either IMHO. Not to say it hasn't been done by the 243Win and even smaller cartridges with good bullets and selective shot placement but a quartering away bull at 300 yards as Mike Dettore suggested? Not me. I would consider that to be a 270Win minimum scenario.
Of course there is a huge difference between someone who lives in elk country and has lots of opportunity and someone who travels long distance for a 5 day hunt.
