Remington's most powerful .30-caliber commercial cartridge. On the rebated-rim Ultra Mag case, it generates more energy than .300 Weatherby Magnum and approaches .30-378 Weatherby territory — in a standard-length action.
Type: Rifle
Introduced: 1999, United States
Parent case: 7mm Remington Magnum
Standardization: SAAMI
Bullet diameter: 0.308" (7.82 mm)
Case length: 2.85" (72.39 mm)
Overall length: 3.6" (91.44 mm)
Max pressure: 65,000 PSI
Rim type: Rebated
Primer: Large Rifle Magnum
Typical twist rate: 1:10
Muzzle velocity: 2900–3300 fps
Muzzle energy: 3360–4353 ft-lbs
Effective range: 600 yd
Common bullet weights: 180, 200, 220 gr
Primary use: Hunting, Target
Production status: Active
Also known as: .300 RUM · .300 Remington Ultra Mag
History: Remington introduced the Ultra Mag family in 1999–2000 on a large rebated-rim case that fit standard-length bolt faces. The .300 RUM pushed 180-grain bullets to 3,250 fps, delivering flat trajectories and long-range terminal energy for elk, moose, and large bears. The main limitation is barrel erosion: the high velocity and large powder charge accelerate throat wear significantly. Remington,…
Notable firearms: Remington Model 700, Remington Model 673
Similar cartridges: .300 Weatherby Magnum, .300 Winchester Magnum, .300 Norma Magnum