Designed by the British firm Holland & Holland, the .300 H&H Magnum was introduced in 1925, based on the .375 H&H Magnum case necked down to .30 caliber. By 1888 the famous Mauser company of Germany had designed a rimless cartridge which gave reliable feeding in bolt action magazine-fed rifles, influencing cartridge design worldwide. The belted case was first introduced by Holland & Holland on the .400 and .375 NE cartridges in 1904 followed by the famous .375 H&H magnum in 1912 with the .300 H&H magnum arriving 13 years later.
The .300 H&H magnum was a proprietary cartridge patented by Holland and Holland, meaning that no other manufacturer could build rifles or ammunition for the .300 H&H magnum without the firm’s consent. For these reasons, the .300 H&H magnum initially received little attention outside of Britain’s upper class. During the later 1920s, Holland & Holland released the patent rights to the .375 and .300 cartridges, allowing Griffin & Howe, along with other manufacturers, to build rifles and ammunition in these calibers. Still, for nearly a decade the .300 H&H magnum went mostly unnoticed by the general shooting public. But in 1935, American shooter Ben Comfort used a Griffin & Howe .300 H&H Magnum built on an M1917 action to win the 1000-yard Wimbledon cup.
Following the Wimbledon Cup victory, the .300 H&H Magnum cartridge obtained widespread attention in the U.S.A, influencing future cartridge designs. The .300 H&H magnum was in its heyday, enjoyed both as an African plains game cartridge, a North American game cartridge and an effective competition chambering. The .300 H&H magnum is a potent cartridge, thoroughly suited to medium game hunting as well as large animals, such as zebras or wildebeests. Eventually, the .300 H&H magnum was superseded by newer .30 caliber magnum cartridges including the .300 Weatherby Magnum, followed by the .308 Norma and .300 Winchester Magnums. Nevertheless, the .300 H&H magnum continues to see use.
