If you're wondering which caliber is the best for elk, you're asking the wrong question. Caliber is the diameter of the bullet. A 30-caliber could be a powerful .300 Weatherby Magnum throwing a 180-grain bullet 3,200 fps or a puny 300 AAC Blackout coughing up a 140-grain slug at just 2,000 fps. Big difference.
The real questions are what is the best elk cartridge and bullet? The cartridge is the complete package: case, primer, powder and bullet. The bullet is the most important because it's the only part that kills the elk. Everything else just drives it. But the powder supply is important, too, since it determines how fast that hardworking bullet leaves the station.
Over the years, hunters have rather arbitrarily chosen 1,500 foot pounds of energy as the minimum for taking an elk cleanly. The fact that thousands of elk have been felled by 30-30 Winchesters and 243 Winchesters suggests this is a bit overstated. Many westerners even use 22-250 Remingtons to take elk. Not recommended, but can be done.
What we really want is a reasonable compromise of bullet diameter and weight, velocity and felt recoil in a rifle we can carry over hill and mountain day after day. A .50 BMG and 700-grain bullet would certainly deliver a big punch to any elk, but who wants to carry the 20-pound rifles that shoot them?
30-caliber is the wrong answer to the wrong question. All of these are 30 caliber cartridges, but not all are ideal for elk hunting.
So, you might want to start with rifle weight matched to your physic, endurance and hunting grounds. At about 170 pounds and just under 6 feet, I find I hunt farther, harder and longer with a 6-pound or lighter rifle than a heavier one. Recoil doesn't bother me much, so I'll take these chambered in anything up to 300 WSM. I'll cheat a bit by using 165-grain or lighter controlled expansion bullets like Barnes TTSX, Nosler Accubond, Swift Scirocco and the like for deep penetration.
This penetration thing is a big deal with elk because they're big and beefy. The softer a bullet and the more it expands on impact, the less it penetrates. Wide surface area, more friction, less penetration. So you want a bullet that will expand 1.5 to 2X its original diameter, not flatten like a pancake or roll up like a ball. Weight retention matters because that also increases penetration via inertia.
Choose a bullet that does this and any cartridge from 26-06 Remington upward can work perfectly well. None will knock an elk down unless you hit the central nervous system from above the front shoulder forward to the brain itself. Sometimes a double shoulder hit will tip an elk over, but not often. Sometimes shock will inspire one to collapse with a lung hit, but I wouldn't count on that, either. I pumped two 180-grain Accubonds from a 300 Win. Mag. into a bull's shoulder and neck from 40 yards last October and all he did was turn around. I put another in his neck, but missed the spine. He stood there for about five seconds before wobbling and falling over.
This is typical. Hemorrhaging causes blood pressure to drop. The brain gets oxygen starved and the animal feints, then expires.
Expecting a bullet from a shoulder fired rifle to knock an elk over is wishful dreaming at best. Remember, for every action there is an equal and opposite reaction. If the rifle doesn't knock you over, how's the bullet going to knock a 700-pound elk over?
Vital tissue damage is what kills elk, and that's where bullet performance beats power all to heck. You want a bullet that reaches the vitals and breaks them down. Since arrows do this regularly with about as much knockdown energy as a hard thrown marshmallow, you can expect bullets to do it, too. Any bullet that expands to reveal a ragged, tattered front will rip more heart and lung tissue and cause more hemorrhaging than one with a smoothly rounded nose.
Armed with this wisdom, you are free to select any legal rifle cartridge with which you can comfortably and reliably deliver such a bullet to your elk. You're much better off with a 6.5 Creedmoor or 7mm-08 Remington delivering the right bullet to the right spot than a 378 Weatherby Magnum blasting the wrong bullet to the wrong spotor even the right spot. Yes, too soft a .338 bullet landing on a bull's shoulder at 2,900 fps could damage a lot of meat and fail to reach the vitals.
Elk country is often steep, vast and hard to negotiate. Spomer took this bull from 450 yards with a 280 Ackley Improved and 150-grain Barnes TTSX bullet fired from a sub-6-pound Rifles, Inc. bolt-action zeroed with a Leupold VX3 2.5-8X scope.
Some of the most popular elk rounds these days are the 7mm magnums, .300 Magnums and 338 magnums. The exact one doesn't matter nearly as much as the bullet it shoots and how well you place it.
Now, you're probably disappointed that I haven't crowned the 338 Win. Mag. as the ultimate elk cartridge. Many claim it is, but that doesn't mean the lighter kicking 338 Federal wouldn't be more effective for many shooters. Or the 280 Rem., 300 Rem Ultra Mag. or 270 Win. There are just too many variables and too many great options to pronounce any one as the ultimate.
Worry more about the bullet and where you place it than the cartridge that sends it.