A Magnum cartridge is a firearms cartridge with a larger case size than, or derived from, a similar cartridge of the same bullet caliber and case shoulder shape. The term derives from the .357 Magnum, the original such cartridge.
.300 Win. Mag.
The .300 Winchester Magnum (also known as .300 Win Mag or 300WM) (7.62×67mmB) is a belted, bottlenecked magnum rifle cartridge that was introduced by 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 (7.62 mm) bullet. The .300 Winchester is extremely versatile and has been adopted by a wide range of users including hunters, target shooters, military units, and law enforcement departments. Hunters found the cartridge to be an effective all-around choice with bullet options ranging from the flatter shooting 165 grain to the harder hitting 200+ grain selections available from the factory. 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. It is a popular selection for hunting moose, elk, and bighorn sheep as it can deliver better long range performance with better bullet weight than most other .30 caliber cartridges. Military and law enforcement departments adopted the cartridge for long range sniping and marksmanship. As a testament to its accuracy, since its introduction it has gone on to win several 1,000-yard (910 m) competitions.
.375 H&H Mag.
The .375 H&H Magnum also known as .375 Holland & Holland Magnum is a medium-bore rifle cartridge introduced in 1912 by London based gunmaker Holland & Holland. The .375 H&H cartridge featured a belt to ensure the correct headspace, which otherwise might be unreliable, given the narrow shoulder of the cartridge case. The cartridge was designed to use cordite which was made in long strands – hence the tapered shape of the case, which, as a beneficial side effect also helped in smooth chambering and extraction from a rifle's breech. The .375 H&H often is cited as one of the most useful all-round rifle cartridges, especially in shooting large and dangerous game. With bullet weights ranging from 270 grains (17 g) to 350 grains (23 g), it has the necessary punch for small to medium game, as well as large, thick-skinned dangerous game. The most common bullet weight available in this caliber is 300 grains (19 g). In many regions with thick-skinned dangerous game animals, the .375 H&H is seen as the minimum acceptable caliber, and in many places (primarily in Africa) it is now the legal minimum for hunting such game. African game guides, professional hunters, and dangerous game cullers have repeatedly voted the .375 H&H as their clear preference for an all-round caliber if they could have only one rifle. Alaskan game guides have expressed a similar preference for brown bear and polar bear country.Unlike many other calibers, .375 H&H Magnum rifles achieve nearly the same point of impact over a wide range of bullet weights at all commonly used distances. This simplifies a hunter's choice in selecting different bullet weights, based upon the game hunted, by requiring fewer scope or sight adjustments, which further serves to popularize the .375 H&H Magnum among professional hunters.[