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.300 H&H Magnum

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 was used by American shooter Ben Comfort to win the 1000-yard Wimbledon Cup Match at Camp Perry in 1935, and it was used again to win the international 1,000 yard competition in 1937. Winchester chambered the Model 70 in .300 Holland & Holland Magnum in 1937.

Design & Specifications
The CIP treats the .300 H&H Magnum and the .30 Super Belted Rimless H&H as separate entities and provides separate entries for the cartridges. There are minute but significant variations with regard to dimensions between the two cartridges. While both cartridges are regulated by the CIP only the .300 H&H Magnum's chamber is regulated by the CIP. The CIP does not provide chamber dimensions for the .30 Super. Although cartridges are generally considered interchangeable, chambers conforming to the strict minimum chamber of the .30 Super may not be able to chamber the .300 H&H Magnum. Both cartridges are based on .375 H&H Magnum cartridge design which provides an increase in capacity over many other cartridges. They feature tapering bodies and very shallow shoulders which prevent them from headspacing reliably on their shoulders. The belt plays a useful role in these cartridges in that it provides a demarcation point for reliable headspacing of the cartridge. : :CIP compliant .300 H&H Magnum schematic diagram : :CIP compliant .30 Super schematic diagram : Significantly the shoulder vertex calculated by the CIP for both cartridges is given as for both cartridges. As the CIP uses the shoulder vertex length as an index to provide correct headspacing for the cartridge, this indicates that the cartridges are dimensionally interchangeable. However, as the .30 Super is rated for a lower pressure, the .300 H&H Magnum cartridge should not be fired in a .30 Super. However, the .30 Super can be discharged in a .300 H&H Magnum rifle. As most significant difference between the cartridges was that the .30 Super was loaded to a far lower pressure than the .300 H&H Magnum. The .30 Super drove a bullet at while the .300 H&H Magnum was loaded with the same bullet at . ==See also==
Source: Wikipedia ↗
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