The .338 Hunter Wildcat, a “New and Improved” .338 Magnum

By Kevin Madsen

I purchased a new software program “Load from a Disk” By Wayne Blackwell and Intelligration Systems Group and wanted to try it out. I put it to work in developing a new .338 cartridge for the standard magnum action. I originally thought that improving on the .338 Winchester Magnum, the most popular medium bore cartridge of the smokeless powder era, would be an easy task. The motivation to improve the .338 Win. Mag. was in part due to the trend of introducing larger volume short cases in many calibers, yet no common ones in .338 caliber for the standard magnum action.

The .338 Win. Mag. is definitely in a different class than the commonly used small bores that include the .30-06, .270, 7mm, etc. It lunches a 67 percent heavier (250 grain) bullet with over 20 percent higher cross sectional area along the same bullet path as the 150 grain bullet from a .30-06. The medium weight 225 grain bullet in the .338 Win. Mag. has a similar trajectory to the .300 Magnums with their 200 grain “heavy bullet.”

I was confident that I could design an “improved” .338 caliber case with the extra recoil tamed by adding a muzzlebrake or even by reducing loads as needed, factory loads offer this alternative for many cartridges. All I had to do was mimic Winchester’s Short Magnums, cartridges marketed as having a resemblance to the shape of the PPC cartridge series and/or Remington’s new Ultra Mags while focusing on the .338 caliber in the standard length magnum action. After a few trials, I thought I had developed an improved .338 case. It had the capacity of 96.2 grains of water, the relative case volume of the 6mm PCC round and the actual case volume of the long/magnum length .340 Weatherby Magnum. However, I soon learned that the case had a design problem common to the “Short” and “Ultra” Mags. I had made a major incorrect assumption (one of many) that a 0.55” diameter case would reliably feed in a standard, unaltered magnum bolt action.

Unfortunately, reality soon set in. The case was designed with a rebated rim and would require an action wider and of greater diameter than the standard magnum action or reduced magazine capacity to accommodate its .550" head diameter, which is much larger than the standard .532" bolt face. The rebated rim design increases the chance that a cartridge will not feed from the magazine, because the bolt has less of a chance to catch the rim as it slides forward to chamber the round. This risk of not chambering a round can be disastrous during a once in a lifetime hunt, for a rifle carried as protection in the field, or when hunting dangerous game. Any .338 Magnum will be viewed as a potential dangerous game cartridge and hunting dangerous game requires maximum feeding reliability for quick follow-up shots; a feeding failure could result in serious injury or death.

After conversations with Guns and Shooting Online Managing Editor Chuck Hawks, I set new objectives for my new cartridge to see if I could “improve” on the .338 Win. Mag. in case functioning and power. Note that it was not a requirement that the new cartridge be based on any existing case; this is a "from the ground up" exercise. However, experienced wildcatters and reloaders should be possible to re-form .375 Ruger cases to make suitable .338 Hunter brass. My objectives are listed below:

  1. A rimless bottleneck case with a full diameter .532" rim using the current magnum bolt face standard of .532" with increased case capacity.
  2. A neck length of 1.2 times bullet diameter.
  3. A shallower shoulder angle (closer to 20o than 25o and definitely not 30o).
  4. A case taper less than that of the .338 Win. Mag, (0.0221/1.820) = 0.0121 inch/inch.

The Starting Point:

.338 Winchester Magnum

  • Case type: Belted Magnum
  • Case capacity: 83.6 grains of water
  • Neck: ID 0.338" OD 0.369", length 0.331" (.98 times caliber)
  • Shoulder: OD 0.491"
  • Shoulder angle: 25 degrees
  • Shoulder taper: 122/0.129 =.946
  • Head diameter: 0.513" directly in front of belt
  • Case length: 2.5"
  • Base to shoulder: 2.040"
  • Base to neck: 2.169"
  • Case taper: (0.0221/1.620) = 0.0121 inch/inch
  • Wall thickness at base: 0.035" (T1)
  • Wall thickness at shoulder: 0.017" (T2)

The New Cartridge:

.338 Hunter

  • Case capacity: 89.3 grains of water
  • Neck: ID 0.338", OD 0.369", length 0.406" (1.20 times caliber)
  • Shoulder: OD 0.500", taper 0.131/.166 = .730
  • Shoulder angle: 20 degrees
  • Web: OD 0.532", length 0.200
  • Case length: 2.5"
  • Base to shoulder: 1.928"
  • Base to neck: 2.094"
  • Case taper: (0.032/1.728) = 0.0185 inch/inch (midway between that of the .375 H&H and Wby. Mags)
  • Case wall thickness at base: 0.032" (T1)
  • Case wall thickness at shoulder: 0.016" (T2)

The Result:

  • The case capacity increased by 7% or 5.7 grains compared to .338 Win. Mag.
  • Neck length is 1.2 times caliber vs. 0.98 times caliber
  • Shoulder angle is 20o vs. 25o to maximize feeding reliability
  • Case taper is 0.019 vs. 0.012

The design of a new .338 Magnum case was achieved according to my objectives. This case should be better for hunting, right? Well, probably not. The odds are that it will never have a case formed for it or much less a cartridge loaded into a hunting rifle. It was a fun time and almost all of my new objectives were met. However, my initial capacity goal of 96 gr. of water was not achieved; to accomplish this many of the other “improvements” could not have been achieved.

I improved the case using a non-standard method. I did not shorten the case neck, decrease case taper and/or increasing shoulder angle. I had “improved” it in reverse to increase reliably and function, while still achieving a modest increase in case capacity.

Excessive recoil is the major reason that very few medium bores have become popular with North American hunters. However, the .338 Hunter does have redeeming qualities. Unlike the WSM and Rem. Ultra Mag and SAUM cartridges, the .338 Hunter should be at least as reliable in the field as the .338 Win. Mag. (theoretically even more reliable). The case uses a full diameter rim, thus avoiding the feeding problems inherent in rebated rim designs. The shoulder angle is not at as sharp, which increases the ease of feeding the cartridge from the magazine. The longer neck length provides a firmer grip on the bullet, reducing bullet movement while the cartridge is stored in a magazine, holding the bullet straighter and allowing the use of a wider assortment of bullet shapes. By careful load selection, the recoil could be reduced to .338 Win. Mag. levels, or less, as required.

Unlike most new cartridges, the .338 Hunter is not a radical design. Because it was conceived as a hunting cartridge, it does not look like a bench rest cartridge or boast the exaggerated features that today are seen as necessary in creating a buying frenzy. However, it demonstrates that cartridges can be improved in practical, rather than trendy, ways. Case capacity does not have to be the only objective in “improving” a case. One can focus on numerous variables while still increasing case capacity.

Some hunters feel that the .338 Win. Mag. already kicks too much and smaller capacity medium bore cases (such as the .338 Federal) are more apt to fill a niche. Moreover, there are plenty of .338 Magnums even more powerful than the Winchester version. These generally compromise feeding reliability or require the use of long (.375 H&H length) actions and the byproduct of increased velocity is heavier recoil.

Anyone buying such a cartridge should understand that these massive magnums create recoil similar to cartridges that are allowed for dangerous game in Africa, where .375 caliber is usually the legal minimum. (Granted, this makes no sense, but the law is the law.) If you might someday embark on an African safari, a .375 medium bore might be a better choice than a big-cased cartridge of less than .375 caliber. Cartridges such as the .375 H&H give you the option to hunt dangerous (lion and CXP4) African game.

However, the North American hunter can feel confident knowing that the .338 Hunter is more than adequate for all large and/or dangerous North American game, including bison, moose and the great bears. The .338 Hunter could be the right cartridge for you!

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Copyright 2008, 2012 by Kevin Madsen and/or All rights reserved.