The .300 H&H Magnum Cartridge was introduced by the British company Holland & Holland as the Super-Thirty in June, 1925. The case was belted like the .375 H&H Magnum, and is based on the same case, as also is the .244 H&H Magnum. The belt is for headspace as the cases' shoulders have a narrow slope rather than an actual shoulder. More modern magnums continue this practice, but headspacing on the belt is not necessary with their more sharply angled shoulders. The cartridge won the 1000-yard Wimbledon Cup Match at Camp Perry in 1935, and the international 1,000 yard competition in 1937. Winchester chambered the Model 70 in .300 Holland & Holland Magnum in 1937.