As I pointed out in my article "The Ever Popular .30 and .303 Rifle Cartridges," this is the most popular group of rifle cartridges in the world, for both military and sporting purposes. Military use is beyond the scope of this article, but the success of the .30 calibers as hunting cartridges is undeniable.
From the little .30 Carbine through the .30-30, .300 Savage, .308 Winchester, .30-06 Springfield, and the various .300 Magnums, the .30 calibers have always been best sellers. Whether the game in question is fox, deer, antelope, elk, moose, or grizzly bear there is a .30 caliber cartridge suited to the job. No other family of cartridges can claim this versatility, although the smaller 7mm (.28) and larger 8mm (.32) families come close.
But which, I got to wondering, is the optimum .30? At what point is the balance between killing power, trajectory, and recoil of a .30 caliber rifle cartridge optimized? Clearly, the .243 Winchester is a better varmint cartridge than any .30, and a .338 Magnum is better brown bear medicine than any .30. So, as versatile as the .30's calibers are, there is a point somewhere in-between these two levels at which the caliber is optimum. Stray too far in either direction in terms of game size and at some point another caliber becomes a better choice.
The .30-30 Winchester is the most popular medium range CXP2 class game cartridge ever devised. Its recoil is sufficiently moderate that most hunters, even those who don't shoot much in the off season, can shoot it well. But, although it can do the job, something more powerful is generally recommended for tackling large CXP3 class game. And for all its virtues, the .30-30 is not a long range cartridge. With most loads its MPBR is around 225 yards.
The .300 Savage is an excellent cartridge, more powerful and flatter shooting than the .30-30. But the .308 Winchester has put the .300 Savage on the skids, as it is a little more of a good thing.
In fact, the .308 is probably pretty close to our optimum cartridge. Quite capable of humanely taking the most common species of CXP3 game yet not so powerful as to be overkill on the smaller CXP2 species. And the .308 shoots flat enough to be useful for hunting plains and mountain game. It is also adaptable to short action rifles, which are all the rage these days. Yes, the .308 would be a definite contender for the "Optimum .30 caliber" title. But, due to its short case, it is limited in one respect; it does not handle the heaviest bullets well.
Just slightly more powerful than the .308 is the venerable .30-06, the most popular big game cartridge in the world. This old timer requires a standard length action, but can deliver, in spades, on all CXP2 and CXP3 class game, and shoots slightly flatter than the .308 to boot. It has a longer case and a longer neck, which allows it great versatility in bullet selection. Using very long 220-250 grain bullets the .30-06 has even accounted for CXP4 class game, including African elephant.
I guess that pretty much settles it. No .30 caliber cartridge is really appropriate for CXP4 class game, but the fact that the .30-06 has accomplished this feat many times certainly indicates that more power in a .30 is pointless. There is no game animal on this planet that the .30-06 has not and can not humanely take.
By that reckoning the .300 Magnums are not optimum .30's. They kick harder than the .30-06 without meaningfully exceeding its killing power. Some of the new short magnums, due to their bullet limitations, don't even equal the killing power of the .30-06 on large game. And they all kick more.
The .300 Mags shoot flatter than the .30-06, but for plains and mountain hunting there are many calibers that shoot just as flat as the .300's and kick less, while remaining completely adequate in killing power. These include standard cartridges on the order of the .25-06 and .270 Winchester as well as the .257, .264, .270 and 7mm Magnums.
For large CXP3 class game the .300 Magnums fail to deliver the killing power of the medium bore magnums. (Compare the .300 Win. Mag. to the .338 Win. Mag. some time and see what I mean.) Nope, the .300 Magnums are neither fish nor fowl, and they are past the point of diminishing returns for the caliber. They are impressive cartridges, but they are not the optimum .30's.
When the U.S. military replaced the .30-40 Krag with a new and more powerful cartridge they made a pretty good choice. And inadvertently created the optimum .30 caliber hunting cartridge.