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Click on figure to access ANSI technical cartridge drawing

A commercial cartridge, probably the consumate "magnum" hunting cartridge. Introduced by Winchester in 1963 as the last of a series of trimmed and necked 375 H&H based magnum hunting cartridges [458 WM - in 1956, the 264 and 338 - 1958].

Its introduction provided a 300 H&H plus some 30 caliber hunting cartridge, but one which would function in a less expensive 30-06 length action [the 300 Wby was available at the time, and provided significant performance over the H&H, but it required the same more expensive to produce H&H magnum length action]. Some contend Winchester did not intend to introduce a 30 caliber magnum (seeing the niche well taken by the dominate and then only 32 year old 300 H&H), but seeing the unexpected popularity of the 30-338WM wildcat based on its 338, and then the introduction in 1962 of Remington's 7mm Mag, decided/were prompted to introduce its updated 300 H&H, the 300 Win Mag. Since then the cartridge has been the world's standard 30 caliber magnum hunting cartridge. Likewise, since then, given it popularity, essentially every bolt action hunting rifle maker of significance has or does offer a 300WM chambering. [Of note, of a contrary nature: with the introduction of many 300 WM pretenders/contenders in the late 1990's - maybe the 300's days are numbered, but then again, maybe not.]

The case based on a 300 H&H, trimmed (by .230") and blown out (but with a subcaliber neck unlike the simply necked down 30-338). Because of the extreme body taper of the H&H, the Win Mag even with its trimmed length, provides a significantly larger case capacity - 87.0gr (of water)full case, 79.5gr with a flat base bullet seated .400", than its parent, 81.3 and 73.8gr, respectively. Other 30 caliber rifle cartridges provide, in comparison (full case): the 30-06, 68.2; 300 Rem SAUM, 73.5; 300 WSM, 80.4; 30-338WM, 81.5; 300 Wby, 91.0; and the 300 RUM, 110.2gr. [Of note, the 300WM is almost exactly twice the 44.0gr of the 30-30.] Given the amounts of powder the 300 burns and the imparted bullet energies, its recoil runs 30% over a 30-06.

The 300WM as a hunting cartridge is viable on any North American game. Some call it: an updated 30-06, which shoots flat like a 270, but hits like a 375 H&H. It was probably American's first heavy cross canyon hunting cartridge [7mmRM in 1962 first light]. In the target realm, it's commonly used for 500 yard thru 2000 yards matches.

Nominal bullet diameter is .308". ANSI lists the maximun average load pressures as: 54kCUP and 64kPSI.