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Remington Big Four Ultra Magnum Cartridges

If you need velocity without the propellant expense of even bigger cases, a Remington Ultra Magnum cartridge may be for you.

Remington Big Four Ultra Magnum Cartridges

Compared to the massive, belted .30-378 Weatherby (right), the non-belted .300 RUM case is smaller, yet it provides more velocity than many other .300-caliber Magnums.

The decade that bridged the change of centuries in 2000 was a fertile time for new rifle cartridges. Between 1999 and 2001, Remington introduced four Magnum cartridges that covered almost everything from deer to dangerous game.

Remington picked the most popular starting point—.30 caliber—and developed a new, large-capacity case about 2.8 inches long to create the .300 Remington Ultra Mag. Remington had finally answered Winchester’s 1963 debut of the still-popular .300 Winchester Magnum. Better late than never.

To me, the non-belted case was the most significant feature of Remington’s Ultra Mags (RUM), boosting a welcome trend toward non-belted “magnums.” As I’ve written many times, most belted cases do not need a belt. Its original function of supporting the firing pin blow has been largely supplanted by generous case shoulders on most cartridges. Going beltless, when possible, commonly translates to improved accuracy and, for handloaders, better case life.

The back end of the Ultra Mag case is very close to the British .404 Jeffery case. The Jeffery’s case-head diameter is 0.545 inch at the extraction cannelure (the CIP dimension convention), and the RUM drawing shows 0.550-inch diameter at a reference point 0.200 inch forward of the base (SAAMI’s convention). However, my sample .300 RUM cases read 0.545 inch at the same place the Jeffery is measured. A rebated 0.534-inch rim conveniently fits the H&H boltface. RUM cases feature a 30-degree shoulder angle and 0.65 degrees of body taper. All share a max cartridge overall length (COL) of 3.600 inches.

Ultimately, four RUM cartridges covered 7mm, .30 caliber, .338 caliber, and .375 caliber. Their maximum average pressure is 65,000 psi.

Three RUMs faced well-established competitors. Winchester owned the .300 and .338 Magnum classes, and H&H ruled the .375 caliber niche. Only among 7mm Magnums was an existing Remington cartridge (the 7mm Remington Magnum) the most popular.

How do the RUMs compare to their competition when handloaded? For consistency, I used velocity data from Hodgdon’s excellent online Reloading Data Center. I chose what I consider the three most appropriate bullet weights for big-game hunting in high-volume cartridges.

To begin, in a 2009 Shooting Times column I wrote, “…I came away with the impression that the 7mm and .300 Remington Ultra Mags were cartridges waiting for a new generation of consumer propellants….”

I think that wait is over.




The 7mm RUM performed very well. It led the pack with 140-, 160-, and 175-grain bullets, showing a roughly 150 fps advantage over the 7mm STW and 200 to 250 fps over the 7mm Rem. Mag. Its closest challenger was the 28 Nosler, which drove a 175-grain bullet within 30 fps of the RUM with less propellant. Still, the 7mm RUM showed a measurable velocity advantage over older, well-established .28-caliber cartridges.

The .300 RUM jumped into a crowded popularity contest dominated by the .300 Win. Mag. With 165- and 180-grain bullets, the RUM posted an advantage of from 100 to 250 fps over older front-runners and still maintained a 100-fps advantage with 200-grain bullets. The RUM is challenged by the newer 30 Nosler and bested by the capacious—and belted—.30-378 Weatherby. The latter burns more propellant than the Remington and the Nosler entries.

To me, the .300 RUM is sitting in a comfortable spot for practical velocity dominance in the .30-caliber playground. Why? The non-belted case is a big plus, and I think many reloaders considering the .30-378 will ask, “At today’s costs, how much propellant can I afford to pour into this case?”

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When we first developed .338 RUM reloading data for the Speer loading manual in 2006, I was quickly impressed by the statistical data. Almost all propellants showed exceptionally low variation in pressure and velocity across the range of safe charge weights, even with “light” 200-grain bullets. That seldom happens in big cases. The .338 Lapua bettered the. 338 RUM with 200- to 250-grain bullets, but they were roughly equal across 275-grain loadings. The massive .338-378 Weatherby still ruled, but not by much.

In .375 caliber, displacing the classic .375 H&H in shooters’ minds is tough duty, and the H&H is still respectable against the “upstarts.” However, the .375 RUM had a 200-fps advantage with 235- and 270-grain bullets and over 300 fps with 300-grainers. That’s expected; case capacity advantages commonly show up with heavier bullets. Again, the roomy .378 Weatherby case posted big numbers, but its advantage over Remington was usually only 100 fps or less at the cost of far more propellant.

So it appears my concerns of 2009 have been resolved with today’s propellant selection. Handloaded, the RUMs made Remington very competitive in the caliber niches where they compete.

Let me repeat what I consider the strongest advantage of the newer Magnums, including the RUMs, over older, more established Magnums: the non-belted case. If you handload, it cures a lot of ills and eliminates advanced handloading operations that belted cases many require.

A couple of reminders for handloaders of these and other mega-cartridges. First, big .30-caliber cases are ballistically more efficient with heavier bullets. Typically, deviations in pressure and velocity increase within shot strings as bullet weight decreases.

Second, handloaders need to rely on newer, tougher bullets designed for higher velocities. This gets very important when the bull elk you expected to be at 250 yards steps out at 75 yards instead. At such velocities, tough bullet construction is a must. Fortunately, we have excellent choices today.

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