British company Holland & Holland introduced the .300 H&H Magnum in 1925. Initially called the “Super-Thirty,” it was designed to hunt African plains animals – all of which it can harvest except the very largest. The .300 H&H Mag has also been successfully employed for elk hunting, as well as taking moose and other large game animals in North America. Popular not only among hunters, competitive target shooters have also used the .300 H&H successfully, with the first major victory taking place at the 1935 Wimbledon Cup, where Ben Comfort's win exposed the cartridge to hunters and target shooters alike. By 1937, Winchester released the Model 70, chambered for the .300 H&H Magnum. In the process, the cartridge was cemented as a global leader of high-performance magnum cartridges for years to come.
Bullet weights for this cartridge are available between 150 grains and 220 grains, muzzle energy can exceed 3,700 foot pounds, and muzzle velocities can exceed 3,300 feet per second. The case for the .300 H&H Mag is based on Holland & Holland's most popular cartridge – their .375 H&H Magnum. They necked down the case to accept a 0.309" bullet, belted it and gave it a narrow sloping shoulder. While it is unusual to see a narrow shoulder like this, the .300 H&H Magnum has proven to have superior ballistics to the .30-06. With a heavy bullet that moves fast, a high ballistic coefficient and a range beyond 200 yards – the hunting community took notice of these numbers immediately. Even as far as 400 yards out, the .300 H&H retains about 2,000 foot pounds of energy.
When the .300 Winchester Magnum was introduced in the 1960s, the .300 H&H Magnum declined in popularity. Some voices of the gun culture speculated that only the fine double-barreled rifles made by H&H were what kept the cartridge alive, but it has experienced a new growth in popularity over the past few years, likely due to manufacturers selling bullets on the leading-edge of ballistic technology. Federal, for example, sells Nosler Partition bullets and Barnes Triple-Shock bullets in the .300 H&H Magnum cartridges they manufacture.