The 375 Remington Ultra Mag (RUM), first used in Africa in 2000 with great success, was officially introduced in 2002. It is based on the unbelted 300 Ultra Magnum case necked up, which is based on the fat (.550-inch) 404 Jeffery case but with a rim rebated to .534-inch. The 2.850-inch case requires a full-length action. With its larger case capacity the 375 RUM is at least 200 feet per second faster than the 375 H&H, thus shooting flatter and delivering considerably more energy--over 5000 foot-pounds with both 270 and 300-grain bullets. Recoil is considerably greater than the 375 H&H, but performance on large game is quite similar to the 416 Rigby and Remington Magnum. Perhaps because of its heavy recoil it has not become popular; Remington is the primary supplier of both rifles and ammunition.
