.300 H&H Magnum

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.300 H&H Magnum
Type	Rifle
Place of origin	United Kingdom
Production history
Designer	Holland & Holland
Designed	1920
Manufacturer	Holland & Holland
Produced	1920
Specifications
Parent case	.375 H&H Magnum
Bullet diameter	.309 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	1-10"
Primer type	large rifle magnum
Ballistic performance
Bullet weight/type	Velocity	Energy
150 gr (9.7 g) GRSL	3,362 ft/s (1,025 m/s)	3,766 ft·lbf (5,106 J)
165 gr (10.7 g) SP	3,213 ft/s (979 m/s)	3,783 ft·lbf (5,129 J)
180 gr (12 g) SP	3,077 ft/s (938 m/s)	3,785 ft·lbf (5,132 J)
200 gr (13 g) HPBT	2,913 ft/s (888 m/s)	3,769 ft·lbf (5,110 J)
220 gr (14 g) RN	2,743 ft/s (836 m/s)	3,676 ft·lbf (4,984 J)
Test barrel length: 26" Source: Reloading data at Accurate Powder

The .300 Holland and Holland Magnum Cartridge first became available in 1925.^[1] 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 international 1,000 yard competition in 1937, and Winchester chambered the Model 70 in .300 H&H in 1939.^[1]

The .300 H&H has what is referred to as the "H&H mystique". It is surprisingly soft-shooting, with a whoosh rather than the abrupt recoil and crack of the .30-06. Ballistically similar to a beefed-up .30-06, the .300 H&H is just 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.^[1] Its case length calls for a full-length magnum action, longer than for the .30-06. It is not nearly as popular as the .30-'06, and never was; but because of its mystique the .300 H&H keeps hanging on despite its repeatedly reported demise. The .300 H&H is an exceptionally fine African plains game cartridge, and suitable for all but the most dangerous big game and pachyderms.