300 Winchester Magnum

The .300 Winchester Magnum (also known as .300 Win Mag or .300 WM) (7.62×67mmB, 7.62x66BR) is a belted, bottlenecked magnum rifle cartridge that was introduced by the Winchester Repeating Arms Company in 1963. The .300 Winchester Magnum is a magnum cartridge designed to fit in a standard rifle action. It is based on the .375 H&H Magnum, which has been blown out, shortened, and necked down to accept a .30 caliber (7.82 mm) bullet.2002, ''Lyman Reloading Handbook, 48th Edition''

The .300 Win Mag is extremely versatile and has been adopted by a wide range of users including big game hunters, target shooters, military units, and law enforcement departments.

Many hunters have found the cartridge to be an effective all-around choice with bullet options ranging from the flatter shooting 150 grain to the harder-hitting 200+ grain selections available in factory ammunition. The .300 Win Mag remains the most popular .30 caliber magnum with American hunters, despite being surpassed in performance by the more powerful .300 and .30-378 Weatherby Magnums and the newer .300 Remington Ultra Magnum, .300 Norma Magnum, .30 Nosler, and 300 PRC. It is a popular selection for hunting moose, elk, and bighorn sheep as it can deliver better long-range performance with heavier bullet weights than many other .30 caliber cartridges. Military and law enforcement departments adopted the cartridge for long-range use, particularly by snipers. As a testament to its accuracy, following its introduction, it went on to win several competitions.

Cartridge history

Prior to the advent of the .300 Winchester Magnum there were already a number of .30 caliber (7.62 mm) cartridges billed as offering a “magnum” level of performance. Such rounds included the .30 Newton of 1913 and the .300 H&H Magnum of 1925. The .30 Newton saw limited commercial success, however, and the .300 H&H was too long for the standard length Mauser and Springfield rifle actions of the time, barring substantial modifications.

Beginning with the .270 Weatherby Magnum in 1943, Roy Weatherby introduced a popular line of rifle cartridges based on the H&H case shortened to fit a standard length () action. The Weatherby cartridges of any given caliber followed a formula of “improved” design, which entailed “blowing out” the H&H Magnum parent case, thereby reducing case taper and increasing usable powder capacity. The .300 Weatherby Magnum, an “improved,” full-length cartridge derived from the .300 H&H was introduced in 1944.

The larger manufacturers soon noticed Weatherby's standard length magnum case, and in due time followed suit. From 1956-1959, Winchester introduced three such cartridges: the .264 Winchester Magnum, .338 Winchester Magnum and .458 Winchester Magnum, all based on the shortened and blown out .375 H&H Magnum case. The popular .30 caliber's omission from that lineup prompted a response by the shooting community and Winchester’s competition. Wildcatters soon produced the .30-338 Winchester Magnum and Norma Projektilfabrik, who were by now manufacturing ammunition for Weatherby, took the standard length basic Weatherby brass and necked it down to .30 caliber (7.62 mm) to form the .308 Norma Magnum.

The .300 Winchester Magnum was introduced in 1963 by Winchester for use in the Model 70 rifle. Winchester developed the .300 Win Mag by taking the .338 Winchester Magnum, which was introduced in 1958, moving the shoulder forward by and lengthening it by . This resulted in a cartridge with a neck somewhat shorter than the diameter of the bullet. Some gun writers have speculated that, had the cartridge been released earlier, its dimensions would have more closely matched the .30-338 Winchester Magnum wildcat cartridge.

The .300 Winchester Magnum was not an instant success, mainly due to competition from the comparable 7mm Remington Magnum cartridge introduced in 1962. However, interest among hunters and shooters grew with time, and it gradually became the most popular of the magnum cartridges.

The .300 Winchester Magnum's broad availability in popular rifles such as the Winchester Model 70, Ruger M77, Remington Model 700 and Weatherby Mark V, together with the wide availability of ammunition from a number of manufacturers, made the cartridge a popular choice among hunters and competitive shooters the world over. Although the .300 H&H Magnum, .300 Weatherby Magnum, .30-338 Winchester Magnum, and the .308 Norma Magnum had a head start on the .300 Win Mag, most of these cartridges eventually faded into obscurity. Only the .300 Win Mag and the .300 Weatherby Mag survived into the 21st century as readily available cartridges, with the Winchester round by far the more popular of the two. New .30 caliber magnums have since been introduced, including the .300 Winchester Short Magnum, .300 Remington Ultra Magnum, .30 Nosler, and 300 PRC; however, none of these have achieved the popularity that the .300 Win Mag retains.

Design and specifications

The .300 Winchester Magnum uses the same case head design of the .375 H&H Magnum, its parent cartridge, though the taper of the round has been significantly reduced in order to ensure greater case volume. The larger dimensions of the .300 Win Mag compared to the .308 Norma Magnum and .30-338 Winchester Magnum cartridges ensures that rifles chambered in such rounds can readily be rechambered to the .300 Win Mag, though the shorter neck of the longer round necessitates comparable bullets must be seated more deeply in the case.

Cartridge dimensions

The ammunition standards organizations SAAMI (Sporting Arms and Ammunition Manufacturers' Institute) and C.I.P. (Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives) have provided specifications for the .300 Winchester Magnum cartridge. Almost no divergence between C.I.P. and SAAMI dimensional values exist for this cartridge.

However, case volume varies from manufacturer to manufacturer to such an extent that the reloading software suite QuickLOAD provides five differing cartridge case capacities for the cartridge.
The SAAMI specification .300 Winchester Magnum case capacity is 91.5 grains of H₂O (5.93 ml).

According to QuickLoad, the case capacities of .300 Win Mag brass produced by four ammunition manufacturers measure as follows:

Remington 88.0 grains of H₂O (5.70 ml)

Federal 92.0 grains of H₂O (5.96 ml)

Winchester 93.8 grains of H₂O (6.08 ml)

Norma 95.5 grains of H₂O (6.19 ml)

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.300 Winchester Magnum SAAMI cartridge dimensions. All sizes in inches (in) and millimeters (mm). The projectile diameter should be 0.309 in (7.85 mm)

SAAMI recommends a bore diameter of and a groove diameter of . SAAMI recommended a six-groove barrel with each groove being wide. Recommended twist ratio is 1:10 (254 mm).

C.I.P. defines the common rifling twist rate for this cartridge as 254 mm (1 in 10 in), 6 grooves, Ø lands = , Ø grooves = , land width = , and the primer type is large rifle magnum.

The SAAMI Maximum Average Pressure (MAP) for this cartridge is piezo pressure (54,000 CUP).

According to the official C.I.P. (Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives) rulings the .300 Winchester Magnum can handle up to P_max piezo pressure. In C.I.P. regulated countries every rifle cartridge combo has to be proofed at 125% of this maximum C.I.P. pressure to certify for sale to consumers. This means that .300 Winchester Magnum chambered arms in C.I.P. regulated countries are currently (2013) proof tested at PE piezo pressure.

Performance