In 2001 Remington introduced their .338 Ultra Mag, based on the .300 Ultra Mag case necked up to accept .338" bullets. This huge cartridge requires a long magnum action as well as an extra long barrel (28" is recommended and 26" is the practical minimum). Despite its outsized case, the .338 Ultra Mag is essentially the ballistic twin of the .340 Weatherby Magnum. The Ultra just burns more powder and kicks harder to achieve the same result. It is, nevertheless, a very effective cartridge.

Remington offers two factory loads for the .338 Ultra, both with 250 grain bullets. One uses a 250 grain Core-Lokt bullet and the other a Swift A-Frame bullet, both at a claimed muzzle velocity (MV) of 2,860 fps and muzzle energy (ME) of 4,540 ft. lbs. The figures at 200 yards are 2440 fps and 3303 ft. lbs.

Here are some specifications for the .338 Ultra Mag that are important to reloaders: Bullet diameter .338", Maximum COL 3.675", Maximum case length 2.825".

Reloading for the .338 Ultra opens up the possibility of using bullet weights other than 250 grains, although given the size of the .338 Ultra case the 250 grain bullet would seem to be the best choice for most applications. As with other .338 caliber cartridges, bullets ranging from 200-250 grains are popular. Due to the .338 Ultra Mag's huge case, slow burning powders such as H4831, RETUMBO, IMR 4831, IMR 7828, RL-22, and RL-25 are most suitable.

The sixth edition of the Hornady Handbook of Cartridge Reloading shows that their 225 grain bullets in front of 82.5 grains of RL-22 powder achieve a MV of 2700 fps. A maximum load of 91.0 grains of RL-22 can drive the same bullets to a MV of 3000 fps.

Also according to Hornady reloading data, 82.4 grains of RL-22 powder can drive their 250 grain bullets to a MV of 2600 fps, and a maximum load of 91.8 grains of RL-22 powder can drive a 250 grain Hornady bullet to a MV of 2900 fps. These Hornady loads used Remington brass and Rem. 9 1/2 primers, and were tested in the 26" barrel of a Remington Model 700 rifle.

Note: A more extensive article covering the .338 Rem. Ultra Mag can be found on the Rifle Cartridge Page.