It's instructive to compare the grand old .300 Holland & Holland Mag. with the .300 Win. Short Mag. because while bullet diameter is the same, cartridge case design has evolved greatly from 1925 to today.
We'll begin with the grand old .300 H&H, or Holland Super .30, as it was originally known. It was the offspring of the venerable .375 H&H and was necked down to accept .30 caliber bullets while still retaining the same long 2.850-inch case.
Its profile is the picture of Victorian elegance: a long, tapered case with a gently sloping shoulder, lengthy neck and a big belt. With a case capacity of 72.2 grains of water, it beats the .30-06 in terms of velocity and energy, and in 1935 it gained notoriety when Ben Comfort used a rifle chambered for this caliber to win the prestigious Wimbledon 1,000-yard target competition. Winchester offered it in its then-new Model 70 in 1937, and soon American hunters got on board.
But the .300 H&H's place atop the .30 caliber magnum market was short-lived. Roy Weatherby improved the .300 H&H case to create the more powerful .300 Wby. Mag. in the 1940s, and in 1963 Winchester introduced the .300 Win. Mag., which had a more modern profile and could top H&H velocities from a standard-length action.
In 2000, Winchester introduced a new, even more efficient .300 with its headstamp: the .300 Win. Short Mag. It could fit in short, stiff actions — which translated to light, handy rifles — and it could achieve .300 Win. Mag. performance with less powder and moderate recoil. By that time there was a sea of .30 caliber offerings, but the .300 WSM stood out.
The .300 WSM is the antithesis of the old .300 H&H. Its 2.1-inch case has straight walls; a steep, relatively short shoulder; and no belt. It also bests the .300 H&H's case capacity by about 10 percent. This means the .300 WSM can beat the old H&H, but not by much — especially if you handload.
In terms of bullet selection and powders, there are ample options in each category for both rounds, but factory ammo is more widely available for the .300 WSM. The same is true for rifles; there are more factory rifles available in .300 WSM today from companies like Winchester, Browning, Kimber and Savage.
If you're looking for a new (or relatively new) H&H CZ's Safari Classics line offers a .300 H&H with a Mauser action. Browning offered a limited run of X-Bolts in .300 H&H, and there are some Ruger No. 1s chambered for it, but they aren't always easy to find.
If you're a fan of old rifles, though, the .300 H&H is your only option. There are classic Winchester 70s to be had for a premium, as well as some Remington 721s. If you're a fan of lever guns or semiautos, the .300 WSM is your gun; Browning offers the BLR and the BAR chambered for that round.
The .300 WSM is a better option for those looking for a light, compact mountain rifle. Shorter actions and shorter barrels equate to lighter, handier guns, and there are a number of really good, light .300 WSMs on the market today.
In terms of accuracy potential and effectiveness on game, both cartridges exist in the same space and can do many of the same things, and both have a well-deserved reputation for accuracy. The H&H's rather archaic case design may lead one to believe that it somehow isn't as accurate as more modern rifles, but there's too much evidence that clearly shows that a good .300 H&H is capable of producing exceptionally tight groups.
One of the classic pre-'64 Model 70s or a new CZ will cost more than an off-the-shelf .300 WSM, but the .300 H&H has a lot of fans, and chances are you won't lose money if you invest in one of these rifles and later decide you want to sell it.