The .338 Win. Magnum Versus the .338 Super Magnums (.330 Dakota, .340 Wby. Mag., .338 RUM, .338 Lapua Mag. and .338-378 Wby. Mag.)

By Gary Zinn

The .338 Winchester Magnum, introduced in 1958, set a performance level for the caliber that most subsequent .338 cartridges have struggled to exceed. However, five current commercial cartridges have surpassed the .338 Win. Magnum's ballistics. These are the .330 Dakota, .340 Weatherby, .338 Remington Ultra Mag, .338 Lapua Magnum and .338-378 Weatherby.

I am not a fan of these cartridges, because they provide a poor benefit to cost ratio. These .338 "super magnum" cartridges achieve marginally better ballistic performance than the .338 Winchester Magnum, but with a lot more sound, fury, reduced availability and greatly increased monetary cost. Here, in summary form, is my case against the super magnums, including the good, bad and ugly.

The Good

These cartridges are steps up in power (muzzle velocity and muzzle energy for given bullet weights) from the .338 Win. Mag. The successive increases in power are in the order I listed the cartridges above, except that the .340 Weatherby and .338 Remington Ultra Mag (RUM) are ballistic (but not interchangeable) twins.

The muzzle velocity data below are top velocity loads from the Hornady Handbook of Cartridge Reloading, 9th Edition. I used this single data source for consistency and convenience. Data for the .338 Win. Mag. was taken in a 24 inch barrel, while the .330 Dakota data are for a 25 inch barrel, with 26 inch barrels used for the .340 Weatherby and .338 RUM. A 24-1/2 inch barrel was used for the .338 Lapua and a 28 inch barrel (!) for the .338-378 Weatherby.

(According to Remington estimates, figure about 30 fps velocity gain for each inch of barrel longer than the industry standard of 24 inches. For example, subtract 120 fps from the Hornady .338-378 velocity figures if the cartridge were fired from a rifle with a 24 inch barrel. -Editor.)

Using 185, 200, 225, and 250 grain bullet weights for reference, the 330 Dakota will drive these bullets 50-100 f.p.s. faster than will the .338 Win. Mag. and this pattern of incremental velocity increases continues with each cartridge in the sequence. At the top end, the .338-378 Weatherby drives these four bullet weights from its 28 inch barrel about 250, 300, 400 and 300 f.p.s. faster than does the .338 Win. Mag.

Averaging across the four bullet weights, here are the percentage increases in muzzle velocity of each super magnum over the .338 Win. Mag. (These figures, and all that follow, are NOT corrected to account for the different barrel lengths.):

  • .330 Dakota, 2.8%
  • .340 Weatherby and .338 RUM, 6.5%
  • .338 Lapua, 7.4%
  • .338-378 Weatherby, 10.9%

The only practical reason for designing a cartridge to drive a given weight bullet faster is to enhance the downrange performance of the bullet. Downrange performance can be summarized with two statistics: maximum point blank range (MPBR) and retained energy at that range.

Starting with MPBR, across the four bullet weights the .338 WM gets an average MPBR (+/- 3 inches from line of sight) of 284 yards. The .330 Dakota has a comparable average MPBR of 292 yards, the .340 Weatherby and .338 RUM 301 yards, the .338 Lapua 304 yards and the .338-378 Weatherby 312 yards. The percentage advantages of these over the .338 Win. Mag. are:

  • .330 Dakota, 2.8%
  • .340 Weatherby and .338 RUM, 6.1%
  • .338 Lapua, 6.9%
  • .338-378 Weatherby, 10.0%

These results are for the Hornady 185-grain GMX, 200 and 225 grain SST and 250 grain InterLock SP bullets.

Turning to retained energy at or near to MPBR, I used the ballistics calculator at to calculate energy at the 25 yard increment closest to the MPBR of each cartridge and load. The extreme spread in this variable is from 2366 ft. lbs. for a 185 grain bullet in the .338 Win. Mag. to 3384 ft. lbs. for the .338-378 Weatherby with a 225 grain bullet. Retained energy of the first load is at 300 yards and of the second at 325 yards.

The lightest load carries over a ton of energy at 300 yards and the heaviest over a half ton more. Either way, and for all loads in between, that is a lot of wallop!

Across the four bullet weights for each cartridge, the retained energy at MPBR averages are 2557 ft. lbs. (.338 Win. Mag.), 2656 ft. lbs. (.330 Dakota), 2883 ft. lbs. (.340 Weatherby and .338 RUM), 2902 ft. lbs. (.338 Lapua) and 3053 ft. lbs. (.338-378). The percentage advantages of the other cartridges over the .338 Win. Mag. are:

  • .330 Dakota, 3.9%
  • .340 Weatherby and .338 RUM, 12.8%
  • .338 Lapua, 13.5%
  • .338-378 Weatherby, 19.6%

Clearly, the .338 super magnums perform better than the .338 Win. Mag. However, in the real world there is no such thing as a free lunch. Thus, the question becomes, what is the cost for the incremental performance gains of the super magnum cartridges?

The Bad

Ballistically, the price of getting the performance gains summarized above is that the energy (i.e. powder charge) inputs required to get them are considerable. For example, 72.4 grain of IMR 4350 powder will drive a 200 grain bullet at 3000 f.p.s. in the .338 Win. Mag., while a charge of 107.9 grains of Viht N-165 is needed to drive the same bullet at 3300 f.p.s. in the .338-378. That is 49% more powder to get 10% more muzzle velocity (MV).

Across the four bullet weights, the average powder charge used to get top MV in each cartridge is:

  • 71.5 grains in the .338 Win. Mag.
  • 77.8 grains in the .330 Dakota
  • 86.9 grains in the .340 Weatherby
  • 91.0 grains in the .338 RUM
  • 96.5 grains in the .338 Lapua
  • 108.4 grains in the .338-378 Weatherby

Another way of understanding the additional powder needed to get increased MV is to list the additional powder to additional velocity percentages of each of the super magnums, relative to the .338 Win. Mag. Averaged across the four bullet weights, these are:

  • 8.8% increase in powder to get 2.8% increase in MV in the .330 Dakota
  • 21.5% increase in powder to get 6.5% increase in MV in the .340 Weatherby
  • 27.3% increase in powder to get 6.5% increase in MV in the .338 RUM
  • 35.0% increase in powder to get 7.4% increase in MV in the .338 Lapua
  • 51.6% increase in powder to get 10.9% increase in MV in the .338-378 Weatherby

To me, the best simple calculation that indicates the relative ballistic efficiency of a given cartridge and load is muzzle velocity divided by powder charge (MV per grain of powder). Averaged across the four bullet weights, the .338 Win. Mag. gets 40.4 f.p.s. of MV per grain of powder burned. Comparatively, the numbers for the other cartridges are 38.3 f.p.s. (.330 Dakota), 35.4 f.p.s. (.340 Weatherby), 33.8 f.p.s. (.338 RUM), 32.2 f.p.s. (.338 Lapua) and 29.4 f.p.s. (.338-378 Weatherby). Dividing the numbers just listed for each other cartridge into that for the .338 Win. Mag. yields the results that the .338 Win. Mag. is:

  • 5.5% more efficient than the .330 Dakota
  • 14.1% more efficient than the .340 Weatherby
  • 19.5% more efficient than the .338 RUM
  • 25.5% more efficient than the .338 Lapua
  • 37.4% more efficient than the .338-378 Weatherby

The Ugly

Using a lot more powder to get a little more velocity has a further cost in recoil and muzzle blast. In a 9.5 pound (field weight) .338 Win. Mag. rifle, the recoil energy of the 200 grain load mentioned above calculates to 30.9 ft. lbs., while the 200 grain load in a 9.5 pound .338-378 rifle would generate 48.0 ft. lbs. of recoil, a 55% difference.

Forty eight foot pounds of recoil exceeds the kick of a 12-gauge, three inch magnum shotgun (about 45 ft. lbs.) and that is a place I do not wish to visit often. The muzzle blast of the .338-378 is also much greater, although I have no way of quantifying that.

The more powder burned equals more recoil and muzzle blast principle applies to all the super magnums, of course. A personal observation: recently I was in attendance when the guest of a fellow shooting club member was putting a .338 Lapua through its paces at our range. No one participating in the exercise ventured to shoot the rifle unless it was resting in a Lead Sled and the rifle, equipped with a muzzle brake, was the loudest thing I have heard short of a Browning .50 BMG.

Here is the last set of bullet points, I promise. Across the bullet weights used, here are the average recoil values for each cartridge in 9.5 pound rifles:

  • 31.8 ft. lbs. for the .338 Win. Mag.
  • 35.2 ft. lbs. for the .330 Dakota
  • 39.9 ft. lbs. for the .340 Weatherby
  • 41.4 ft. lbs. for the .338 RUM
  • 43.8 ft. lbs. for the .338 Lapua
  • 50.4 ft. lbs. for the .338-378 Weatherby

Then, there is the monetary cost of buying and shooting any of these rifles. The rifle bargain here is the .338 Remington Ultra Mag. It appears that a no-frills Remington Model 700 rifle can be purchased in this caliber for $800 to $1000 in 2015, the same price as a good quality .338 Win. Mag. rifle. Remington .338 RUM factory ammo starts at about $4 per cartridge. (Most factory ammo for the .338 WM sells for $2 to $3 per round, with a wide choice of brands and bullet weights available.)

Buying a rifle chambered for any of the other four super magnums is going to put a real strain on the debit card. As best I can determine, a new rifle chambered for any of these calibers is going to set one back a minimum of $2,000.

Also, ammo gets more expensive. It appears that .340 Weatherby and .338 Lapua factory cartridges start at about $4.50 each, while .338-378 Weatherby ammo runs about $7 per cartridge and .330 Dakota cartridges cost about $10 each. Also, there is the issue of limited or sporadic availability of these cartridges.


The .338 Winchester Magnum dominates the .338 cartridge niche, because it is a perfect storm in the bore size. It shoots 180 to 250 grain bullets far, hard and relatively efficiently; it does so without obscene levels of recoil, muzzle blast and expense.

Conversely, the .338 super magnums are far from perfect. They perform only a little better than the .338 Win. Mag., but are ballistically inefficient, loud and kick like the devil. They are also expensive to buy and shoot. For these reasons, none of these cartridges seriously challenges the popularity of the .338 Win. Mag., or is likely to do so in the future.

See Compared: .338 Winchester Magnum, .338-06 A-Square and .338 Ruger Compact Magnum for a look at the .338 Win. Mags. more sensible competitors.

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Copyright 2015 by Gary Zinn and/or All rights reserved.