The first that comes to mind is the .308 Winchester. It will work splendidly on whitetails – I’ve done that – and its sufficient for moose – I’ve done that, too. It’s compact and allows for a properly sized rifle with an ample magazine capacity. With good bullets, 20 inches of penetration is easily obtained, even with 2x bullet expansion. When properly zeroed it will allow you to hold dead on out to just the other side of 300 yards. And, in an 8-pound rifle it will generate less than 20 ft./lbs. of free recoil energy.
An 8-inch kill zone is a reasonable average for North American big game animals. From a trajectory standpoint, the 308 should allow you to hold in the center of this kill zone out to 300 yards and still hit it, even in a moderate cross wind. Given reasonable shot angles, for a bullet to pass through the vitals of all North American big game animals, from pronghorn to moose, it should be capable of penetrating 18 to 20 inches in 10 percent ordnance gelatin. To maximize tissue destruction the bullet should also expand between 1.5 and 2 times its original diameter.
Long cartridges increase rifle length and weight. Fat cartridges diminish magazine capacity. Long and fat cartridges do both. And some magnum cartridges need long barrels to really be magnums. What’s ideal? Eight pounds is a good target weight for a field ready rifle and 40 inches or less is a reasonable length. You must shoot once and a coup de grace might be needed. You also might miss, so you need at least three shots. And, since you never want an empty rifle, capacity must be four or more. That is why this caliber is my choice in the field.