.300 RUM Ballistics, Rifles & Hunting Guide The .300 RUM ballistics, rifles, and hunting applications make this cartridge an important option to understand when comparing large magnum rifle cartridges. Introduced by Remington in 1999, the .300 Remington Ultra Magnum (.300 RUM) was developed to deliver high muzzle velocity and strong downrange performance using .30-caliber bullets. […]