What's plenty of folks? I know exactly two hunters that have used the .243 Win on elk. One because that is the only rifle he managed to keep in a divorce, and another because that was the only rifle he had with him in the truck to put down a wounded cow. I've seen the video of the girl that killed an elk with the .243 as well and have even posted it a few times.
Of course a .243 Win will kill an elk, so will a .223, .22 Hornet, and .22 LR. Just because it is capable of killing something doesn't make it a "credible" elk cartridge. Anyone who has spent time in hunting elk will tell you just becasue it can kill it doesn't make it ideal for the job.
I don't have a hard and fast caliber/cartridge rule myself for elk hunting. Nor do I beleive there is a magical formula for how much energy is required to successfully kill big game. I do however feel that anything 6.5mm and up is a good place to start for elk. There are just better bullet options available starting in the 6.5 range and up when it comes to hunting elk.
No offense, but the "so will..." is not a valid argument. It's a logical fallacy called Reductio Ad Absurdum.
Woman and younger hunters use the .243 on elk regularly and on purpose, unless their husbands/fathers are infected with the magnumitis so prevalent today.
Elk are heavy but they're not particularly thick skinned or heavy boned. They're giant deer for crying out loud. A .243 loaded with 80gr Barnes TTSX will penetrate 3+ FEET in a deer. How thick is an elk? Half that, maybe?
"That video" shows an elk killed with a .243 from nearly 700 yards. Considering that's probably 4 times the average shot distance, how could it even be argued that the .243 isn't a reasonable elk gun?
I have a friend who hunts elk almost every year in CO. He only archery hunts and shoots 315gr arrows out of a 47lb draw weight bow. The same magnumitis from the gun world also infects the archery world. He is regularly told that you need a 70lb bow to kill elk. Mind you, that 70lb requirement has never changed even though today's 50lb bows produced the same or more kinetic energy than a 70lb bow from 15 or 20 years ago, not to mention hunters still use recurves, which tend to make less energy (literally) than a modern 30lb bow. His 47lb bow has *never failed* to fully penetrate an elk.... but you "need" a 70lb bow. Yeah right. What you *need* is to make your shot.
It's no different in the gun world. Bullet technologies and cartridge capabilities evolve, the good ole boys opinions don't.
Good shots are what you need. A bad shot with a .243 isn't going to be a good shoot because you swap in a .300mag. Does a uber-magnum add some effective range? Yeah, probably. Out at 700, 800, 1200 yards, yep. How much does that matter to the average hunter, many (most) of which have never shot that far and literally couldn't hit a house at 1,000 yards.
The difference between a .243 and a .300mag or a .270 or 30-06 or, whatever, at 100, 200, 400 yards, is how much energy the tree on the other side of the animal absorbs.