From Wikipedia, the free encyclopedia:
"The .300 Holland and Holland Magnum Cartridge first became available in 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 won the international 1,000 yard competition in 1937, and Winchester chambered the Model 70 in .300 H&H in 1939.
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 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, longer than for the .30-06. It is not 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 a fine African plains game cartridge, and suitable for all but the most dangerous big game and pachyderms."
.300 H&H Magnum. (2009, January 16). In Wikipedia, The Free Encyclopedia. Retrieved 18:00, March 21, 2009, from http://en.wikipedia.org/w/index.php?title=.300_H&H_Magnum&oldid=264371263