The .338 Remington Ultra Magnum is a .338 caliber rifle cartridge introduced by Remington Arms in 2002.
It is a beltless, rebated rim cartridge based on the .300 Remington Ultra Magnum case shortened .090" and necked-up to accept a 0.338-inch (.338 caliber) bullet. The .338 Remington Ultra Magnum has a similar case capacity as the .338 Lapua Magnum and somewhat lower than that of the .338-378 Weatherby Magnum. It is one of the most powerful .338-caliber rounds in production.