Compared: The .243 WSSM and .240 Weatherby Magnum

By Chuck Hawks

This article is really Winchesters fault, for having the temerity to compare their .243 WSSM to the larger .240 Weatherby in their advertising and promotional material for the .243 WSSM. Winchester, you asked for it so here it is.

The .240 Weatherby Magnum was introduced in 1968 on a unique belted case with about the same capacity, length, and .473" rim diameter as the .30-06 Springfield. It has, since its inception, been the most powerful of all factory loaded 6mm cartridges. Only the European 6x62 Freres even comes close.

Weatherby offers five different factory loads for their .240 Magnum. These drive an 87 grain Hornady Spire Point bullet at a muzzle velocity (MV) of 3523 fps and muzzle energy (ME) of 2397 ft. lbs., a 90 grain Barnes X-Bullet at a MV of 3500 fps and ME of 2448 ft. lbs., a 95 grain Nosler Ballistic Tip at a MV of 3420 fps and ME of 2467 ft. lbs., a 100 grain Hornady Interlock at a MV of 3406 fps and ME of 2576 ft. lbs., and a 100 grain Nosler Partition also at a MV of 3406 fps and ME of 2576 ft. lbs. The 87 grain Hornady Spire Point bullet is a combination varmint and medium game bullet, all of the other bullets are intended primarily for big game hunting.

The .240 would seem well suited for hunting javelina, antelope, deer, sheep, goats, feral pigs, black bear, and caribou. The 100 grain Nosler Partition bullet is probably the best alternative for the largest game, up to about 400 pounds, that one might reasonably hunt with Weatherby's .240 Mag.

Weatherby offers the .240 Magnum in several of their Mark V rifle models, including the SBGM, Ultra-Lightweight, Accumark, Fibermark, Fibermark Satinless, Stainless, Synthetic, Sporter, and their flagship Mark V Deluxe. All Weatherby .240 rifles are supplied with 24" barrels as of this writing, although they used to be offered with 26" barrels. Weatherby considers their powerful .240 Magnum a big game cartridge and does not offer it in their Super VarmintMaster models.

Winchester introduced the .243 WSSM 35 years later. They offer a Supreme varmint load that drives a 55 grain Nosler Ballistic Silvertip bullet at a MV of 4060 fps and ME of 2013 ft. lbs. That is the highest velocity factory load I can remember since the introduction of the .17 Remington in 1971. Only the .220 Swift, introduced in 1935, claims a higher MV (48-50 grain bullets at 4110 fps).

As shooters discovered back in the 1930's with the Swift, ultra-fast velocity also means ultra-fast barrel wear. It is hard to see the point of this load, as its very stubby bullet will lose velocity faster and drift more in the wind than the common 55 grain .22 caliber varmint bullets. Experience has shown that bullets weighing 70-87 grains are about right for shooting varmints with a 6mm cartridge, but no such load is offered for the .243 WSSM at this time.

Winchester offers two loads for the .243 WSSM intended for big game hunting. One of these is a Supreme 95 grain Ballistic Silvertip bullet at a MV of 3250 fps and ME of 2258 ft. lbs. This is a moly coated version of the same Nosler Ballistic Tip bullet that Weatherby uses in one of their .240 Magnum factory loads. This should be a good bullet at .243 WSSM velocities for javelina, pronghorn antelope, feral goats, and small to medium size deer.

The other .243 WSSM factory offering is a Super-X load using a 100 grain Power Point bullet at a MV of 3110 fps and ME of 2147 ft. lbs. This may be the best .243 WSSM load for North American feral pigs, mule deer, sheep, mountain goats, black bear, and other game than might weigh up to about 300 pounds.

Browning and Winchester have announced special super short actions for the WSSM series of cartridges. Big game and varmint style rifles are offered. The varmint models come with 24" barrels; the sporter versions of the Browning A-Bolt II come with 21" barrels and the sporter versions of the Model 70 come with a 22" barrels. Winchester .243 WSSM sporter models are the Featherweight and Black Shadow; the Coyote is the varmint model.

Browning WSSM versions of the A-Bolt II are the Medallion, Composite, and Stainless sporter models, plus their Varmint rifle. The actual release of all Browning WSSM rifles has been delayed due to feeding problems and very short barrel life with hot WSSM loads.

Both the .243 WSSM and .240 Wby. Mag. are at their best with bullets weighing between 70 and 105 grains, although other weights are offered. Both cartridges use the same 6mm/.243" diameter bullets.

Loaded to the maximum permissible pressure the .240 Weatherby shoots flatter with the same weight bullet than the .243 WSSM because it has significantly greater powder capacity and also operates at slightly higher pressure (53,500 cup compared to 52,000 cup). For example, comparing 95 grain factory loads using Nosler plastic tipped bullets in both calibers, we can see on the "Rifle Trajectory Table" that the .240 bullet has a maximum point blank range (+/- 3") of 327 yards, compared to a MPBR of 312 yards for the .243 WSSM.

With identical 100 grain bullets and full power loads the "Rifle Trajectory Table" shows that the .240 Weatherby has a MPBR of 322 yards, compared to only 296 yards for the .243 WSSM. Figuring the maximum point blank range shows the optimum trajectories for both cartridges. Using a 200 yard zero for both cartridges and calculating the drop at longer range (as Winchester does) would simply magnify the difference between the two cartridges, making the .240 look even better.

So how about the misleading Winchester comparison showing the .243 WSSM to have slightly less drop than the .240 Weatherby? How did they do that? Simple, Winchester's graphs are comparing a reduced pressure .240 load at a MV of 3200 fps to their full power .243 WSSM factory load at a MV of 3250 fps. Naturally, if you under-load the .240 to a velocity 50 fps below that of the .243 WSSM, the latter will have a slightly flatter trajectory. It's a completely bogus comparison, of course.

This takes misleading advertising in the gun world to stratospheric heights. All that it really proves is the old adage that figures can lie and liars can figure. Given bullets of identical ballistic coefficient (BC), higher velocity always makes for a flatter trajectory.

Here is how that Winchester table would look if they showed full power factory loads (Weatherby and Winchester respectively) for both cartridges using the 95 grain Nosler bullets (BC .379) zeroed at 200 yards.

  • .240 Wby. Mag. (MV 3420 fps): -5.1" at 300 yards, -15.1" at 400 yards, -31.0" at 500 yards.
  • .243 WSSM (MV 3250 fps): -5.8" at 300 yards, -17.0" at 400 yards, -34.9" at 500 yards.

Due to its higher velocity with identical bullets the .240 Weatherby Magnum generates higher energy at all ranges. Again using the 95 grain factory loads as an example, the energy figures in foot-pounds look like this:

  • .240 Weatherby Mag (MV 3420 fps, ME 2467 ft. lbs.): 2087 at 100 yards, 1759 at 200 yards, 1475 at 300 yards, 1229 at 400 yards.
  • .243 WSSM (MV 3250 fps, ME 2258 ft. lbs.): 1898 at 100 yards, 1610 at 200 yards, 1359 at 300 yards, 1140 at 400 yards.

These figures are taken from the published ballistics of the respective factory loads. The .243 WSSM ballistics were achieved in 24" test barrels, while the .240 Weatherby ballistics were achieved in 26" test barrels. The average big game hunting rifle will have a barrel 2" shorter than the test barrel in either case (3" shorter for the Browning .243 WSSM big game rifles). Subtract 100 fps from the claimed MV of both cartridges to get an approximation of the actual velocity in the shorter barrels supplied by the rifle manufacturers. The point to remember is that the relative relationship between the performance of the two cartridges will remain the same.

In terms of performance, no matter what you look at (velocity, energy, or trajectory), the .240 Weatherby Magnum is clearly superior to the .243 WSSM. Since the .240 has greater case capacity and has a slightly higher maximum average pressure limit, it can be no other way. It is literally impossible for the .243 WSSM to equal the performance of the .240 Weatherby Magnum with full power loads, whether factory loads or reloads.

To put the .243 WSSM's ballistics in proper perspective, let's compare all of the reasonably well known 6mm calibers using full power loads with 100 grain bullets (the most popular weight for big game hunting). The list would look something like this (chronographed in hunting rifles with 24" barrels):

1. .240 Weatherby Magnum - 3350 fps.
2. 6x62 Freres - 3300 fps
3 & 4. 6mm-06 wildcat and 6mm-284 wildcat (tie) - 3200 fps.
5 & 6. .243 WSSM and 6mm Remington (tie) - 3100 fps.
7. .243 Winchester - 3000 fps.
8. 6mm BR Remington - 2650 fps.

One thing this list reveals is that a reasonable comparison would be between the 6mm Remington and the .243 WSSM. But instead Winchester chose to compare their new super short "magnum" cartridge to the .240 Weatherby Magnum.

Next, let's take a look at the .243 WSSM and .240 Weatherby Magnum in terms of killing power. According to the "Maximum Optimal Ranges for Big Game" table, using 100 grain bullets at factory load velocities the maximum optimal range on 200 pound game is: 295 yards for the .243 WSSM, and 400 yards for the .240 Weatherby Magnum. With the same factory loads the maximum optimal range on 400 pound game is: 40 yards for the .243 WSSM, and 150 yards for the .240 Weatherby Magnum.

Being the less powerful cartridge, the .243 WSSM generates less recoil in rifles of equal weight. If we compare 7.5 pound rifles shooting 95 grain bullets at claimed factory load velocities in both calibers we get a figure of 10.6 ft. lbs. of free recoil energy for the .243 WSSM (MV 3250 fps), compared to 12.2 ft. lbs. of recoil for the .240 Wby. Mag. (MV 3420 fps).

Note that while 7.5 pounds is probably a reasonable compromise comparison weight for these rifles, a .243 WSSM rifle with a catalog weight of 6 pounds will actually weigh around 7 pounds after it is scoped, while the average 6.75 pound .240 Weatherby rifle probably weighs about 7.75 pounds with a scope. This difference in rifle weight will increase the actual recoil energy of the .243 WSSM and decrease the actual recoil energy of the .240 Weatherby.

The design of the two cartridges should be touched on briefly as it relates to use in hunting rifles. The .240 Weatherby is a normally proportioned, modern hunting cartridge of proven feed reliability in bolt action rifles. On the other hand the extremely short, extremely fat, sharp shouldered, rebated rim .243 WSSM is a nightmare shape in terms of feed reliability. It looks like a jumbo size bench rest cartridge of the 6mm PPC type, which is intended for use only in single shot rifles. And, in fact, that is the design inspiration for the WSSM cartridges.

It also touches on the reason Winchester built special "controlled round push feed" actions for the WSSM calibers instead of using a shortened version of their standard push feed Model 70. The Browning A-Bolt II is a push feed action, and the release of the super short action version of the A-Bolt II has been delayed due to problems with the WSSM cartridges. For those who are interested, I go into the subject of reliability in more detail in the article "Bolt Action Rifles for Dangerous Game" on the Rifle Cartridge Page.

Among the major rifle manufacturers, Browning and Winchester have announced rifles for the .243 WSSM cartridge. Only Weatherby chambers for the .240 Weatherby Magnum. So a new .243 WSSM rifle should should eventually be easier to find than a new .240 Weatherby rifle. Of course, the .240 has been around for a lot longer, and so have Weatherby rifles so chambered, so .240 rifles are more available on the used market.

Both cartridges are available in ultra-light and light weight rifles. The sporter versions of the Browning and Winchester WSSM rifles weigh about 6 pounds. The Weatherby Ultra-Lightweight rifle weighs only 5.75 pounds in .240 Wby. Mag., even though it is supplied with a 24" barrel. The Weatherby Deluxe weighs 6.75 pounds.

I would summarize the .243 WSSM vs. .240 Weatherby Magnum comparison thusly: the .240 is superior in every performance category, period. The performance of the .243 WSSM is actually nearly identical to that of the 6mm Remington cartridge, while the .240 Weatherby is a true magnum cartridge. So if you are looking for magnum performance, the .240 Weatherby is the obvious choice.

If you prefer the Winchester Model 70 rifle you will have to settle for the .243 WSSM, as the big red "W" does not chamber for the .240 Weatherby Magnum. If you prefer the Weatherby Mark V rifle, you will have to get the .240, as Weatherby does not chamber for the .243 WSSM.

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Copyright 2003, 2012 by Chuck Hawks. All rights reserved.