The .300 Winchester Magnum (7.8×67mm), commonly known as the .300 WinMag, is a belted, bottlenecked magnum rifle cartridge that was introduced by Winchester Repeating Arms Company in 1963 as a member of the family of Winchester Magnum cartridges. The .300 Winchester Magnum is a magnum cartridge designed to fit in a standard length action. It is based on the .375 H&H Magnum, which has been blown out, shortened, and necked down to accept a .30 caliber (7.62mm) bullet.
The .300 Winchester Magnum is extremely versatile and has been adopted by many shooting disciplines. The cartridge has found use by hunters, target shooters, military units, and law enforcement departments. Hunters found that the cartridge was an effective all round cartridge. The .300 Winchester Magnum remains the most popular .30 caliber magnum cartridge with American hunters, despite being surpassed in performance by the more powerful .300 Weatherby Magnum 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 1000 yard (910 meter) competitions.