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 .300 H&H Magnum was first introduced by Holland & Holland as the Super-Thirty in June 1925. This cartridge features a case similar to that of the .375 H&H Magnum and shares the same casing, with the .244 H&H Magnum also employing this design.