Announced in 1999 and released in 2000, the .338 Remington Ultra Magnum is one of the four Remington long action ultra magnum cartridges which include the 7mm, 300, .338 and .375 Ultra Magnum cartridges, all loosely based on the 404 Jefferies case design blown out to maximum dimensions. The .338 RUM was initially chambered in Remington’s model 700 Sendero long range rifle. With a rigid stock featuring an aluminum chassis and the M700 action mated to a heavy barrel, the .338 Sendero offered excellent accuracy potential. The Sendero rifle line was begun in 1994 and has been a remarkable achievement in the development of an accurate mass produced factory rifle. Unfortunately the .338 RUM did not achieve major popularity as a chambering for the Sendero and was discontinued in 2002. The .338 RUM has been chambered in other M700 rifles but can also be ordered in its original Sendero configuration from Remington’s custom shop.
The .338 RUM is a well balanced cartridge ideal for hunting large bodied game at close to extended ranges.
Case length of the .338 RUM is 2.760” (70.1mm), being .090” (2.3mm) shorter than the 7mm, .300 and .375 Ultra Magnums which have a case length of 2.850” (72.4mm). This allowed Remington to keep within their preferred cartridge overall length of 3.600” (91.4mm), the M700 action having a magazine length of 3.660” (93mm).
The .338 RUM is capable of achieving identical velocities to the .340 Weatherby and is similar in power to the .338 Lapua.
With regards to COAL’s for long range loads, the .338 RUM is still best served with a Wyatt magazine box when using long sleek bullet designs. Without additional magazine space the RUM is best served with more traditional style hunting bullets (including the SST) but can of course be single fed ammunition loaded with the longest match style bullets, seated out where they belong.
Sometimes called the “poor mans Lapua”, this label certainly fits the .338 RUM. However the same can be said of the .338 Edge which often yields identical velocities with absolutely identical powder charges. The .338 Edge is in turn based on the full length .300 RUM with its more readily available brass. Having said this, there is very little difference between any of these cartridges in power and real world downrange performance. Individual barrel lengths, harmonics and sweet spots certainly muddy the waters. With regards to the Edge, the combination of an extra-long barrel and a long magazine box can help custom built Edge rifles gain performance over more basic factory .338 RUM rifle set ups.
One factor the RUM has in its favor (as does the Edge) is that it utilizes a standard case head (rebated rim) as opposed to the Lapua which features a wider and more unique case rim / bolt face diameter. The Lapua is also slightly fatter throughout and can be better served in an action with a wider cross section, not just for strength but also for the sake of harmonics.
Handloads for the .338 RUM generally produce identical velocities as both the .338 Lapua and .340 Weatherby when each are chambered in 26” barreled rifles. Compared to the .340 Weatherby the .338 RUM has slightly greater powder capacity however .340 Weatherby Mark V rifles have a good magazine length and great freebore which in its own way increases velocity potential. Both the .338 RUM and .338 Lapua are loaded to pressures of between 60,000 and 62,000psi. The Weatherby is designed to operate between 53 and 54,000psi.
