.475 Ackley Magnum (P.O. Ackley Data)

.475 Ackley Magnum (P.O. Ackley Data)

The .475 Ackley Magnum is a large-bore wildcat cartridge developed by P.O. Ackley as part of his extensive work in improving and expanding the capabilities of existing cartridge designs. Known for his “improved” cartridges, Ackley applied similar principles to the development of the .475 Ackley Magnum, creating a powerful round intended for use on the largest and most dangerous game animals. The cartridge reflects Ackley’s focus on increasing efficiency, velocity and overall performance while maintaining reliable function in strong bolt-action rifles.

The .475 Ackley Magnum is generally based on a belted magnum case derived from the .375 Holland & Holland Magnum, modified with reduced body taper and a sharper shoulder angle to increase case capacity. It is necked to accept .475-inch bullets, allowing for a significant increase in frontal area compared to smaller calibers. This design enables the cartridge to achieve higher velocities than many traditional large-bore rounds when loaded with heavy bullets. Data associated with Ackley’s work typically includes bullet weights ranging from approximately 400 to 500 grains, with velocities often exceeding 2,300 feet per second depending on the specific rifle and load.

The cartridge was intended for dangerous-game hunting, particularly for species such as elephant and Cape buffalo where deep penetration and immediate stopping power are essential. The combination of heavy bullet weight, large diameter and high velocity provides substantial energy and the ability to penetrate dense muscle and heavy bone. Bullet selection is critical, with solid projectiles preferred for maximum penetration and controlled-expansion bullets used when greater tissue damage is desired.

Recoil is considerable, reflecting the cartridge’s performance and intended application. Rifles chambered in .475 Ackley Magnum are typically heavy bolt-action rifles designed to safely handle the pressures and recoil associated with large-caliber cartridges. Proper rifle configuration, including stock design and overall weight, is essential for managing recoil and ensuring effective use in the field. As with many Ackley cartridges, careful attention to chamber dimensions and loading practices is required to achieve consistent performance.

The .475 Ackley Magnum remains a specialized cartridge, primarily of interest to enthusiasts of large-bore rifles and Ackley’s work. As reflected in P.O. Ackley’s data, it represents an example of mid-twentieth-century cartridge experimentation, combining increased capacity and performance with practical application for dangerous-game hunting.

Source: Wolfe Publishing (P.O. Ackley Data)