The .45 Winchester Magnum is a .45 caliber rimless cartridge intended for use in semi-automatic pistols. The cartridge is a stretched version of the .45 ACP

.45 ACP

The .45 ACP , also known as the .45 Auto by C.I.P., is a cartridge designed by John Browning in 1904, for use in his prototype Colt semi-automatic .45 pistol and eventually the M1911 pistol adopted by the United States Army in 1911.-Design and history:The U.S...

 with additional strengthening in the web area to accommodate the higher operating pressure. The Win Mag is nearly identical in dimensions and loading to the .45 NAACO developed by the North American Arms Corporation

North American Arms

North American Arms is a United States company, headquartered in Provo, Utah, that manufactures small pistols and mini-revolvers.The company was originally named Rocky Mountain Arms...

 for their Brigadier

NAACO Brigadier

The North American Arms Corporation Brigadier was developed to meet Canadian requirements for a service handgun in the aftermath of World War II. It was based largely on the FN GP35 Hi-Power self-loading pistol of 1935, but scaled up significantly...

 pistol, developed to supply to the Canadian Army after World War II

World War II

World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

. The army ultimately did not adopt the pistol and its non-NATO standard

STANAG

STANAG is the NATO abbreviation for Standardization Agreement, which sets up processes, procedures, terms, and conditions for common military or technical procedures or equipment between the member countries of the alliance. Each NATO state ratifies a STANAG and implements it within their own...

 ammunition.

The cartridge has been used by hunters and metallic silhouette shooters.

General comments

The .45 Winchester Magnum had been on the drawing board two years before its introduction in 1979 by Winchester. The cartridge did not gain much popularity due to the intermittent availability of the Wildey

Wildey

The Wildey is a gas operated, double action/single action, selective fire pistol designed by Wildey J. Moore. The pistol was designed to fire several high pressure proprietary cartridges including the .45 Wildey Magnum and the .475 Wildey Magnum.-Action:...

 pistol and the LAR Grizzly pistol. The cartridge was chambered in the Thompson-Center Contender single shot pistols.

The cartridge provided the shooter a higher performance level than the .44 Remington Magnum

.44 Magnum

The .44 Remington Magnum, or simply .44 Magnum, is a large-bore cartridge originally designed for revolvers. After introduction, it was quickly adopted for carbines and rifles...

in a semiautomatic pistol. The cartridge is able to fire a heavier bullet than the .44 Magnum given similar velocities or similar weighted bullets at higher velocities.

The .45 Winchester Magnum gained a following among IHMSA competitors as it provided the power and performance necessary to knock down targets at an extended range. The cartridge has been used by handgun hunters and is among the few pistol (as opposed to revolver) cartridges which have been adopted for this sport.