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.338 Remington Ultra Magnum


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.  

Factory ammunition

Remington currently offer one factory load for the .338, the 250 grain Corelokt at an advertised velocity of 2860fps for true velocities of around 2780fps. This load produces high shock on game weighing between 90 and 320kg (198-700lb) out to a distance of around 100 yards and clean killing out to ranges exceeding 300 yards. The Corelokt is a soft projectile but stout enough in the shank to ensure penetration through relatively dense muscle and bone. This bullet is adequate for larger (moose) sized game but cannot be relied on to hold together if encountering the heavy ball joints of the front shoulders.
For a time Remington also offered the 250 grain Swift A-Frame but have since dropped this from production. And while the .338 bore has excellent extended range potential, Remington do not offer anything for those interested in this application. Instead, the sole factory CoreLokt load exists as a basic general purpose option while also serving as a source of brass.
Federal also produce just one load for the big .338, the 210 grain Nosler Partition loaded to a velocity of 3030fps. Previously Federal offered the 225 grain Accubond but have since dropped this. Note that a similar load is now available from Nosler. The 210 grain Federal load duplicates what many have achieved using hand loads in the .338 Win mag. This bullet is ideally suited to game weighing between 90 and 180kg (198-396lb) and produces high shock out to around 170 yards. The lightweight Partition will handle raking shots on larger medium game but not tail on shots due to its mild sectional density. On game in the 320 to 450kg (700-1000lb) range the 210 grain Partition is prone to jacket / rear core separation when striking heavy ball joints. Nevertheless this bullet still has great merit. It is a fast killer when used appropriately on large bodied deer. Its mild SD also serves it well in that energy transfer is assured. The slightly lighter weight (rather than 225 or 250 grains) also ensures high impact velocities and high energy transfer at ordinary hunting ranges. Put simply, there is more to this bullet than simply how deeply it will penetrate or what sized game it can tackle.
Nosler loads include the 200 grain Accubond at 3150fps, the 225 grain Accubond at 2975fps, the 250 grain Accubond at 2850fps along with the 250 grain Partition at 2850fps.
Nosler ammunition is very expensive however the loads offered do give .338 RUM shooters (in the U.S at least) some options for ridge to ridge hunting. Readers must understand that without realistic expectations these bullets can prove to be neither fish nor fowl, being too weak in construction for heavy bodied game while the core bonding can make the same bullet too tough for lean game. Nevertheless, one cannot write the Accubond off. This bullet design does have strengths and is quite well suited to larger bodied deer including Elk out to impact velocities of 2200fps. It is also good to see the 200 grain Accubond bullet utilized in a factory load, driven fast in such a way as to make the .338 RUM more useful (potential energy transfer) on light or lean animals (though a non bonded bullet can produce further potential). On the other side of the coin, readers are cautioned as to the limitations of the 250 grain Accubond. This bullet cannot attain the same level of penetration on truly large heavy game in the same manner or style as a heavy Woodleigh bullet.

Hand loading

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.
Using ultra slow burning powders in the 7828/ ADI2217 range average velocities with handloads include 3450fps with the 160 grain Barnes, 3350fps with 180 grain bullets, 3250fps with 200 grain bullets, 3150fps with 210 grain bullets, 3050fps with 225 grain bullets and 2950fps with 250 grain bullets. The 285 grain A-Max / ELD can be driven at around 2700fps while heavy 300 grain bullets yield velocities of between 2600 and 2650fps.  
The .338 RUM should not be confused with the increasingly popular wildcat .338-300 RUM and .338 Edge which use the full length parent .300 RUM case.
Notes on bullet performance can be found in the .340 Weatherby and .338 Lapua texts.

Closing comments

The .338 RUM is a potent hunting cartridge and with modifications to the action in order to house a Wyatt magazine box (or detachable mag box), the RUM can be further exploited as a long range hunting cartridge, utilizing the longest and sleekest of projectiles. Nevertheless, it would seem that the .338 Lapua holds greater appeal at this time of writing purely because of its military history, a factor which always creates civilian interest. The .338 Edge has also overshadowed the popularity of the .338 RUM. Neither cartridge should be seen as exclusively better than the RUM. The Remington cartridge is fine in its own right, along with the excellent Sendero platform.  
Suggested loads: .338 RUM Barrel length: 26”
No ID   Sectional density Ballistic coefficient Observed  MV Fps ME
1 HL 200gr SST .250 .455 3200 4547
2 HL Hornady SF 225gr SST/IB .281 .515 3050 4647
3 HL 250gr Rocky Mountain .281 .846 2950 4830
4 HL 300gr Woodleigh RN .416 .332 2700 4855
Suggested sight settings and bullet paths         
1 Yards 100 175 298 339 350 375 400
  Bt. path +3 +4 0 -3 -4 -6.4 -9.2
2 Yards 100 150 283 325 350 375 400
  Bt. path +3 +3.7 0 -3 -5.4 -8.1 -11.1
3 Yards 100 150 283 325 350 375 400
  Bt. path +3 +3.7 0 -3 -5.2 -7.7 -10.5
4 Yards 50 100 200 232 250 275 300
  Bt. path +.9 +2 0 -2 -3.5 -5.8 -8.7
No At yards 10mphXwind Velocity Ft-lb’s
1 300 5.7 2575 2945
2 300 5.3 2512 3151
3 300 3.3 2622 3815
4 100 .8 2439 3962
338 RUM final
.338 RUM Imperial Metric 
A .534 13.59
B .550 13.97
C 30 Deg  
D .526 13.36
E .370 9.4
F 2.296 58.32
G .330 8.38
H 2.760 70.1
Max Case 2.760 70.1
Trim length 2.750 69.8
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We are a small, family run business, based out of Taranaki, New Zealand, who specialize in cartridge research and testing, and rifle accurizing.