.300 H&H Magnum

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.

:[[Image:300HHMag.png|600px|alt=300 H&H Magnum Schematic|.300 H&H Magnum schematic diagram conforming to CIP dimensions]] :CIP compliant .300 H&H Magnum schematic diagram

:[[Image:30Super.png|560px|alt=30 Super Schematic|.30 Super Belted Rimless H&H schematic diagram conforming to CIP dimensions]] :CIP compliant .30 Super schematic diagram

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Significantly the shoulder vertex calculated by the CIP for both cartridges is given as 91.69 mm 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 180 gr bullet at 2750 ft/s while the .300 H&H Magnum was loaded with the same bullet at 2920 ft/s.

References

The .300 Holland & Holland Magnum by Chuck Hawks (subscription req)

References

1. Saami pressures. (n.d.). Retrieved May 3, 2023, from https://leverguns.com/articles/saami_pressures.htm
2. Barr, Al, Teesdale, Jerald, Keith, Elmer & Hardaway, Ben F. ''Reloading Information (Volume 2)'' 1951 National Rifle Association pp.54-58
3. "Reloading data at Accurate Powder".
4. Hornady, J.W. ''Hornady Handbook'' (1967) Hornady Manufacturing Company pp.196-207
5. Speer, Vernon & Raymond ''Speer Wildcat Loads'' (1956) Speer Products Company p.91
6. [https://dspace.nplg.gov.ge/handle/1234/84132 H&H 1933 catalog]
7. (26 November 2018). ".30 Super Flanged H&H".