.300 Remington Ultra Magnum

.300 RUM cartridge

Type

Rifle

Place of origin

Canada

Production history

Designer

Remington

Designed

1999

Manufacturer

Remington Arms Company

Produced

1999 - present

Specifications

Parent case

.404 Jeffery

Case type

Beltless, rebated rim, bottleneck

Bullet diameter

.308 in (7.8 mm)

Neck diameter

.344 in (8.7 mm)

Shoulder diameter

.525 in (13.3 mm)

Base diameter

.550 in (14.0 mm)

Rim diameter

.534 in (13.6 mm)

Case length

2.850 in (72.4 mm)

Overall length

3.600 in (91.4 mm)

Case capacity

110.2 gr H₂O (7.14 cm³)

Rifling twist

1–10"

Primer type

Large rifle magnum

Maximum pressure

65,000 psi (450 MPa)

Ballistic performance

Bullet mass/type	Velocity	Energy
150 gr (10 g) X	3,456 ft/s (1,053 m/s)	3,979 ft·lbf (5,395 J)
168 gr (11 g) BTHP	3,326 ft/s (1,014 m/s)	4,128 ft·lbf (5,597 J)
180 gr (12 g) BTSP	3,256 ft/s (992 m/s)	4,238 ft·lbf (5,746 J)
200 gr (13 g) SP	3,119 ft/s (951 m/s)	4,321 ft·lbf (5,858 J)
220 gr (14 g) RN	2,970 ft/s (910 m/s)	4,310 ft·lbf (5,840 J)

Test barrel length: 24" (610 mm)
Source(s): Accurate Powder

The .300 Remington Ultra Magnum, also known as the .300 Ultra Mag' or .300 RUM is a 7.62 mm (.308in.) caliber rifle cartridge, 7.62×72mm, or .30 caliber rifle cartridge introduced by Remington Arms in 1999. The .300 Remington Ultra Magnum is one of the largest commercially available .30 caliber magnums currently being produced. It is a beltless, rebated rim cartridge, capable of handling all large North American game, as well as long-range shooting. Among commercially produced .30-caliber rifle chamberings, the .300 Remington Ultra Magnum is second only to the .30-378 Weatherby Magnum in cartridge-case capacity.

In the early 1980s Aubrey White and Noburo Uno of North American Shooting Systems (NASS) based in British Columbia Canada began experimenting with the full length .404 Jeffery by reducing the taper and necking it down to various calibers such as 7 mm, .308, 311, 338, 9.3 mm and .375. These cartridges were known variously as the Canadian Magnum or the Imperial Magnums. Rifles were built on Remington Model 700 Long Actions and used McMillan stocks. Cartridges were fire formed from .404 Jeffery cases with the rim turned down, taper reduced and featured sharp shoulders.

Both Remington and Dakota Arms purchased the formed brass designed by Noburo Uno for use in their own experimentation and cartridge development. In 1999 Remington released the first of a series of cartridges virtually identical to the Canadian Magnum cartridges which featured a slightly wider body, increased taper, and shallower shoulders and named it the .300 Remington Ultra Magnum. Dakota too released their own version of the cartridge but chose not to turn down the rim and shortened the case to work in a standard length action. Remington would go on to design their own shortened versions of the Ultra Magnum cartridge which they were to call the Remington Short Action Ultra Magnum or RSAUM for short.

The .300 Remington Ultra Magnum is a member of the Remington Ultra Magnum cartridge family based on the .404 Jeffery via the Canadian Magnum cartridges. As these cartridges feature wider bodies than the belted magnums based on the .375 H&H case, these cartridges have greater case capacities than their corresponding full length belted Magnum cartridges such as the 7 mm Shooting Times Westerner, the .300 Weatherby Magnum, .340 Weatherby Magnum and the .375 Ackley Improved.

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Wikipedia