Definitions for ".458 Winchester Magnum"
The .458 Winchester Magnum is a rifle cartridge introduced 1956 by Winchester. The cartridge case is based on the .375 H&H case shortened to 2.5 in (64 mm), and "blown out" (case opening enlarged) to accept a bullet of .458 inch (11.6 mm) diameter. With good handloads one can expect approximately 2170 feet per second (660 m/s) using 500 grain (32.4 g) bullets (achieved using a barrel 24 inches (610 mm) in length).