.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.
| .300 H&H Magnum | ||||||||||||||||||||||||
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.300 H&H Magnum (Left) .30-06 Springfield (Right) | ||||||||||||||||||||||||
| Type | Rifle | |||||||||||||||||||||||
| Place of origin | United Kingdom | |||||||||||||||||||||||
| Production history | ||||||||||||||||||||||||
| Designer | Holland & Holland | |||||||||||||||||||||||
| Designed | 1925 | |||||||||||||||||||||||
| Manufacturer | Holland & Holland | |||||||||||||||||||||||
| Produced | 1925 | |||||||||||||||||||||||
| Specifications | ||||||||||||||||||||||||
| Parent case | .375 H&H Magnum | |||||||||||||||||||||||
| Case type | Belted, straight | |||||||||||||||||||||||
| Bullet diameter | .308 in (7.8 mm) | |||||||||||||||||||||||
| Neck diameter | .338 in (8.6 mm) | |||||||||||||||||||||||
| Shoulder diameter | .450 in (11.4 mm) | |||||||||||||||||||||||
| Base diameter | .513 in (13.0 mm) | |||||||||||||||||||||||
| Rim diameter | .532 in (13.5 mm) | |||||||||||||||||||||||
| Rim thickness | .220 in (5.6 mm) | |||||||||||||||||||||||
| Case length | 2.850 in (72.4 mm) | |||||||||||||||||||||||
| Overall length | 3.600 in (91.4 mm) | |||||||||||||||||||||||
| Rifling twist | 1 in 10 in (250 mm) | |||||||||||||||||||||||
| Primer type | large rifle magnum | |||||||||||||||||||||||
| Maximum pressure (C.I.P.) | 54,000 psi (370 MPa) | |||||||||||||||||||||||
| Maximum pressure (SAAMI) | 62,000 psi (430 MPa) | |||||||||||||||||||||||
| Maximum CUP | 54,000 CUP | |||||||||||||||||||||||
| Ballistic performance | ||||||||||||||||||||||||
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| Test barrel length: 26 in (660 mm) Source(s): Reloading data at Accurate Powder | ||||||||||||||||||||||||
The cartridge offered superior ballistics to the .30-06 for long range, and the .300 H&H is almost as versatile with all bullet weights and types, especially if well-developed handloads are used. It excels with the heaviest .30-calibre bullets in the 180–220-grain range. SAAMI has set the pressure limit for this cartridge at 54,000 P.S.I. Its case length calls for a full-length magnum action, and surplus military actions chambered for the .308 Norma Magnum or the .300 Winchester Magnum offered a lower cost alternative for similar ballistics in the 1960s. The long .300 H&H case was designed for loading cordite, and those two modern magnum cartridges offered similar powder volume in a shorter case better adapted to ballistic uniformity with United States Improved Military Rifle (IMR) smokeless powder.
It has never been as popular as the .30-06; but the mystique of well-crafted rifles chambered for the .300 H&H keeps the cartridge in use despite its repeatedly reported demise. The .300 H&H is a fine African plains game cartridge, and suitable for all but the most dangerous big game and pachyderms.
As it was common for rimless hunting cartridges, a rimmed (beltless) variant, at the time called just "Holland's Super .30" and now sometimes named .30 Super Flanged H&H, was developed simultaneously for break-barrel rifles and combination guns.