The .243 WSSM
By Chuck Hawks
For 2003 Winchester announced a pair of new centerfire rifle cartridges based on a radically shortened version of their .300 WSM case, itself a short action caliber based loosely on a cut down version of the huge .404 Jeffery case. These new Winchester Super Short Magnum (WSSM) calibers are designed for a rifle action about 1/2 inch shorter than the usual (.243 Winchester length) short action. The new .243 WSSM, the subject of this article, is one of the original WSSM calibers.
The .243 WSSM retains the rebated rim design of the WSM cartridges. The rim diameter is .535" and the case head is .555" in diameter. The shoulder diameter is .535" and its angle is 28 degrees. Case length is 1.675". The bullet diameter is .243" and the specified rifling twist is 1 turn in 10", the same as for the .243 Winchester. This makes sense as the actual performance of the two cartridges is not that dissimilar.
The .243 WSSM looks like a larger version of the bloated little 6mm PPC. (Which, by the way, was intended for single shot target rifles, not repeaters.) Browning and Winchester were the first gun manufacturers to announce rifles for the .243 WSSM cartridge, based on super short versions of the A-Bolt II and Model 70 bolt actions.
Browning has been forced to delay the actual release of their super short action rifles due to feeding problems (the A-Bolt II is a push feed action) and extremely rapid barrel erosion caused by the high velocity of some WSSM loads. Winchester thinks that they have at least solved the feeding problem with their new hybrid "controlled round push feed" action.
Very short, grossly fat cartridges in the mold of the 6mm PPC target round are touted as the last word in accuracy. To quote from the Olin/Winchester web page, this is due to, "a highly efficient propellant burn . . . and headspacing off the shoulder." (Ordinary rimless bottleneck cartridges, for example the .243 Winchester and 6mm Remington, all headspace off the shoulder!)
There is some truth to this, but I tend to ascribe most of the phenomenal accuracy of bench rest cartridges to the extreme care and attention to detail that goes into reloading them. Perhaps the ultra accurate rifles in which they are fired and the skill of the shooters should also get some of the credit. Older cartridges as ordinary as the .222 Remington and .308 Winchester have also delivered superior accuracy when reloaded with similar care and fired from bench rest rifles.
I think that the popularity of short, fat cartridges is simply a fad, driven by clever marketing. Just as zoot suits were a fad in the 1940's and bell-bottom trousers were a fad in the 1970's. The first fad of the 21st Century has brought us short, very fat, rifle cartridges.
I doubt that the shape of the case actually makes much practical difference (within reasonable limits) in hunting cartridges, even when fired in specialized varmint rifles. Other factors in the rifle/cartridge/load equation are far more important. Conventional .24 caliber rifle cartridges such as the .243 Winchester and 6mm Remington have already demonstrated more potential accuracy than can be realized in a rifle fired from the shoulder in the field.
Winchester offers two deer, antelope, and black bear loads for the .243 WSSM. One of these is a Supreme load using a moly coated 95 grain Ballistic Silvertip bullet (BC .379, SD .230) at a muzzle velocity (MV) of 3250 fps and muzzle energy (ME) of 2258 ft. lbs. At 100 yards the velocity is given as 3000 fps and the energy as 1898 ft. lbs. At 200 yards the velocity is 2763 fps and the energy is 1610 ft. lbs. At 300 yards the velocity is 2538 fps and the energy is 1359 ft. lbs. The trajectory of the 95 grain Ballistic Silvertip bullet looks like this (Winchester figures): +1.2" at 100 yards, +1.1" at 150 yards, 0 at 200 yards, -2.3" at 250 yards, -5.7" at 300 yards, and -16.9" at 400 yards.
The other .243 WSSM factory load designed for hunting medium size game is a Super-X load that drives a 100 grain Power Point bullet (SD .242) at an advertised muzzle velocity of 3110 fps and muzzle energy (ME) of 2147 ft. lbs. At 100 yards the velocity is 2838 fps and the energy is 1789 ft. lbs. At 200 yards the velocity is 2583 fps and the energy is 1481 ft. lbs. At 300 yards the velocity is 2341 fps and the energy is 1217 ft. lbs. The trajectory of that load looks like this (Winchester figures): +1.4" at 100 yards, +1.3" at 150 yards, 0 at 200 yards, -2.6" at 250 yards, -6.6" at 300 yards, and -19.7" at 400 yards.
The Winchester catalog velocities for all .243 WSSM loads were developed in 24" test barrels, but most Browning and Winchester .243 WSSM rifles are supplied with 21" and 22" barrels. Early chronograph test results have shown that actual muzzle velocities delivered range from about 100 fps to 250 fps below those claimed, depending on the rifle and the load.
A 90-105 grain bullet is usually recommended for hunting medium game with any of the popular 6mm cartridges, so the two WSSM factory loads are right in the ballpark. Their killing power is equal to standard factory loads for the 6mm Remington or "Light Magnum" factory loads or hot handloads for the .243 Winchester.
Now let's take a look at the Winchester figures for the .243 WSSM's varmint load. This is a very light 55 grain Supreme Ballistic Tip bullet (BC .276, SD .133), recommended for use on prairie dogs, woodchucks, and coyotes. These are sound recommendations and should not be exceeded with such a relatively light bullet for the caliber. (Standard varmint weight bullets in .243 caliber are 70-80 grains.)
Winchester claims a MV of 4060 fps and ME of 2013 ft. lbs. for their 55 grain Ballistic Silvertip bullet (BC .276, SD .133). This moly coated bullet is traveling at a velocity of 3628 fps at 100 yards, 3237 fps at 200 yards, 2800 fps at 300 yards, and 2550 fps at 400 yards. The trajectory of that load looks like this (Winchester figures): +0.6" at 100 yards, +0.7" at 150 yards, 0 at 200 yards, -1.5" at 250 yards, -3.9" at 300 yards, and -12.0" at 400 yards.
This bullet shoots faster and slightly flatter at all ranges than the 55 grain Ballistic Silvertip bullet loaded in the .223 WSSM cartridge. Barrel erosion at such velocities can be very rapid. Like the .223 bullet it should be used only for varmint shooting. It is designed to break up when it hits a hard surface or a small animal, minimizing danger to livestock, property and people in the semi-populated areas where so much varmint shooting takes place. Do not attempt to use this bullet on animals larger than coyotes.
As can be seen from these figures, from a 24" barrel the .243 WSSM offers performance with all bullet weights equal to or slightly better than the .243 Winchester, and equal to but no better than the 6mm Remington. Most of the advantage over the standard .243 Winchester is lost, however, in the short barrels actually being supplied on Browning and Winchester hunting rifles.
The .243 WSSM is inferior in performance to the 6mm-284 and the 6mm-06 wildcats across the board. This is certainly not "magnum" performance by any stretch of the imagination. The true .24 caliber magnums, such as the European 6x62 Freres and the American .240 Weatherby Magnum, can drive full hunting weight bullets about 200-300 fps faster than possible in the .243 WSSM.
The .243 WSSM is factory loaded close to the allowable maximum average pressure, which means that reloaders are unlikely to be able to improve much on published velocities. However, it should be possible to approximately equal the published velocities with carefully assembled maximum reloads using 55, 95, and 100 grain bullets. And, of course, reloaders can play around with 70, 75, 80, 85, 90, and 105 grain bullets. In the .243 WSSM I would think that 70-80 grain bullets would be most appropriate for varmints and 90-105 grain bullets appropriate for deer and other medium game animals.
The sixth edition of the Hornady Handbook relates that VARGET proved to be an excellent powder for varmint bullets and H4831 and RL-19 good choices for hunting weight bullets in the .243 WSSM. Using Hornady 95-100 grain bullets, 36.8 grains of RL-19 gave a MV of 2700 fps, and 42.1 grains of RL-19 gave a MV of 3000 fps. Winchester WLR primers were used and their custom Browning test rifle had a 26" barrel.
The .223 WSSM's very short and very fat case, wide shoulder, and rebated rim make it a technical nightmare to feed from the box magazine of a repeating rifle. A failure to feed may jam the rifle and cost the deer or antelope hunter a trophy. Unlikely, but stil a point to ponder before plunking one's money down for a .243 WSSM big game rifle. For those who are interested, I explore feed reliability in more detail in my article "Bolt Action Rifles for Dangerous Game."
The .243 WSSM would make a better cartridge for a specialized varmint rifle, especially for use in windy areas, if reloaded with heavier 70-80 grain bullets. The fact that the .243 WSSM works through a super short action is a moot point in this application, since varmint rifles usually have 24" or 26" heavy contour barrels and weigh on the order of 10 pounds.
The .243 WSSM is a high (but not magnum) performance cartridge on the order of the 6mm Remington. It is an effective caliber for game from the size of small varmints to mule deer.
Based on the performance of the .223, .243 and .25 WSSM cartridges, this line of development seems to have reached something of a dead end. The .223 WSSM can match but not exceed the performance of the best existing .22 cartridges (such as the .220 Swift). The .243 WSSM is hard pressed to attain parity with the standard short action .24's (such as the 6mm Remington) and is clearly inferior to the true .24 caliber Magnum cartridges. These facts are reflected in the slow sales of the WSSM calibers.
Copyright 2003, 2012 by Chuck Hawks. All rights reserved.