The "all-round" rifle is a persistent and legitimate Holy Grail among hunters. Can one cartridge/rifle do it all? Absolutely. As long as you don't intend to hunt lions, buffalo or elephants.
    
This means one rifle will suffice for taking hogs, antelope, deer, elk, moose, black bears and even grizzlies. And it can suffice for coyotes and even prairie dogs. It won't be ideal at the extreme ends, but it can work.
    
Before choosing, one must establish his hunting priorities. Are you going to mostly hunt deer with the occasional coyote or elk hunt? Or are you going to hunt elk with the odd deer or coyote hunt?
    
Actually, it doesn't matter all that much, because a .30-06 bolt-action with a 3-9X40mm scope can handle all that stuff. But so can a .300 Win. Mag. or 7mm Rem. Mag. or any of the short magnums in the same calibers. But if you want a little less recoil, there's the .270 Win. or Winchester Short Magnum. Or the 6.5mm-284 Norma, 7mm-08 Rem. ...

The list isn't endless, but nearly so.
    
But how can this be? With hunters arguing year in and year out about whether the .270 Win. is adequate for elk or the .30-06 too slow for pronghorns, how can so many cartridges be suitable for such a wide range of game? Bullet selection.
    
Projectiles play third fiddle to cartridges and rifles in our minds, but bullets are the real heroes in all of this. They do the real work. Everything else is just a support network getting the bullet to its target. So here's the real truth, the critical information hunters need to understand: A projectile that reaches the target and penetrates to and preferably through the vitals is what you need. Not the fastest or heaviest or hardest hitting. As many a midnight poacher can tell you, a .22 Long Rifle used correctly will put elk and moose in the freezer.
    
I'm not suggesting you choose a .22 Long Rifle for your all-around big game rifle, but I won't laugh if you pick the .260 Rem. or a .338 Win. Mag. As long as you use the right bullets for the job and your rifle/scope puts them inside of a 2-inch group, you're good to go to 300, maybe 400 yards if you're an excellent, careful shot.
  
We needn't go into ballistic details for every potential cartridge (at least in this blog post), so let's use the good old .30-06 Govt. as an example. This has proven itself on everything in the world including rhinos, buffalo and I'm sure elephants.

It's often said—and rightly said—that wide bullet selection in .308 cal. is a big part of what makes the .30-06 so versatile. Reasonable power without excessive recoil is another. So here's how you play the game: To maximize ballistic potential, start with a 24-inch barrel. This should add 50-100 fps velocity to most bullets. But if you can't stand that much barrel length, a 22-inch will do just fine. Next, get a bolt action you like and trust—a brand and model with a good, old reputation for reliability and durability. The magazine should hold three to five rounds. You're only going to shoot one or two at each animal because you're going to practice and become a great shot. Six to 8 pounds for the package is about right.
    
Any stock will suffice. Walnut stocked rifles more than 100 years old are still shooting well and consistently. You can glass bed the actions and free float the barrels and not worry about swelling changing point of impact. But if you like synthetic stocks better, get one. Ditto stainless steel over blued chro-moly steel. If you think you'll use open sights someday, get them. Otherwise, save a few bucks and get a smooth barrel. Mount a reputable 3-9X40 or 2.5-8X, 3-10X or 4-16X scope on it. Smaller is easier to carry and less likely to break. Giant objective lenses aren't necessary. Fully multi-coated lenses are. They make 40mm objectives plenty bright enough up to 10X.
    
Now, load a 110-grain bullet on the .30-06 and it'll zip out at about 3,400 fps—perfect for varmints, coyotes and the like. Go with a 130-grain at around 3,100 fps for pronghorns, deer or sheep. Use a 150-grain or 165-grain spire point at 2,900 to 3,000 fps for deer or bears, and a 180- to 200-grain at 2,500-2,700 fps for elk, moose, grizzlies. Done.
    
Fine tune this with careful bullet selection. A controlled-expansion bullet that retains most of its weight (Winchester XP3, Swift A-Frame, Federal Trophy Bonded, Barnes TTSX, etc.) penetrates so well that a 150-grain will penetrate like a 180-grain softer bullet such as a Remington Core Lokt. The lighter bullets will shoot flatter and recoil less than the heavier ones. The heavier ones will retain more energy downrange and drift less in the wind, basic shape remaining constant (i.e. spire points instead of flat nose).
    
And that's it. One gun, all game. The only easier thing would be to settle on one bullet, say a 165-grain, and shoot everything with it. Then you'd learn the trajectory like your phone number and become one of those legendary shots who never misses. One rifle, all game, for a lifetime.
    
By the way, sensible as this is, it's not for me. I enjoy testing and shooting as many rifles and cartridges as possible. But if I had to ...
 

(Pictured above: The custom stainless/walnut Winchester Model 70 in .30-06 topped with a Leupold 2.5-8X36mm scope is a great all-round setup for rifle hunters.)