The .300 WSM (Winchester Short Magnum)
By Chuck Hawks
Winchester's .300 WSM was announced early in 2001. Its fat stubby case has a sharp 35 degree shoulder angle and a .535" diameter rebated rim (to allow operation with standard magnum size bolt faces). The case diameter at the base is .555", its body is 1.664" long to the bottom of the shoulder, and its length is 2.1". The overall cartridge length is 2.86".
This new short action .300 magnum is a powerful, compact cartridge. It is suitable for game from the size of deer and antelope to the largest thin-skinned game worldwide.
The .300 WSM has slightly less powder capacity than the standard length .300 Winchester Magnum. It is at its best with bullets of 150-180 grains. With bullets in this weight range its performance is essentially identical to that of the established .300 Win. Mag. because, allegedly, the short case burns powder slightly more efficiently than the longer case.
The .300 WSM is so similar to Remington's contender in the .300 short magnum sweepstakes (The .300 Rem. Short Action Ultra Mag) that one of them is clearly redundant. Which cartridge will prevail in the market place is undecided as I write this, but the .300 WSM appears to have the early lead in exposure, perhaps because its name is easier for gun scribes to write.
Winchester suggests that their new cartridge's short overall length allows shorter and lighter .300 Magnum rifles to be built. Winchester introduced the .300 WSM in a 7.5 pound Model 70 Featherweight rifle with a 24" barrel. Browning chambers their 6 pound 9 ounce A-Bolt II rifle with a 23" barrel for the WSM line of cartridges.
Unfortunately, all .300 Magnums require a long barrel (26" is standard, and 24" is the minimum length) to burn the amount of powder necessary to achieve their superior ballistics. Cut a .300 barrel to 22" and you are just about as well off with a .30-06.
The main drawback to the .300 WSM is recoil, particularly in the lightweight rifles offered by most manufacturers. A standard weight .300 Mag. rifle kicks plenty hard already, and a light .300 generates recoil that is totally unacceptable to most shooters. Excessive recoil often leads to flinching, which causes inaccurate and erratic shooting. No one is immune from this, although some are less affected than others.
An 8 pound rifle chambered for the .300 WSM rocks the shooter with about 26.3 ft. lbs. of recoil. Tests have demonstrated that the average shooter can't withstand over 20 ft. lbs. of recoil, and many shooters can't tolerate over about 15 ft. lbs., without developing a flinch. The .300 WSM in a lightweight rifle is way over the limit, and the wise shooter will take it in very small doses.
While the .300 WSM is advertised to produce ballistics virtually identical to the popular .300 Win. Mag. with 150 and 180 grain bullets fired in a 24" barrel, heavier bullets protrude so far into the powder space of the stubby case that velocities are reduced compared to standard length magnum cartridges. This limits the .300 WSM's versatility compared to standard length .300 Magnums, particularly for use on very large or dangerous game. In addition, the new .300 Winchester Short Magnum cartridges are so fat that magazine capacity is reduced by one round, clearly undesirable when hunting dangerous game.
The question of potential feeding problems with such a short, fat, sharp shouldered case has been raised, but I have not encountered any reports of actual failures to feed in either Winchester or Browning bolt action rifles. I suspect that this is more of a theoretical concern than a real problem. Nevertheless, it is worth remembering that the original .375 and .300 H&H Magnums were designed with very sloping shoulders partly because they were intended for use on dangerous game and feed reliability was seen as crucially important.
Winchester figures for the .300 WSM with a 24" test barrel claim a muzzle velocity of 3300 fps and ME of 3628 ft. lbs. for the 150 grain bullet. The 200 yard figures are 2834 fps and 2676 ft. lbs.
Winchester claims a MV of 2970 fps with 3526 ft. lbs. of muzzle energy for the 180 grain bullet. The 200 yard figures are 2524 fps and 2547 ft. lbs. Those figures are nearly identical to the velocity of the .300 Winchester Magnum taken in the same length barrel, and also to the figures for the .300 Rem. SAUM in a 24" test barrel.
The trajectory of the .300 WSM will be essentially identical to that of the .300 Win. Mag. with either 150 or 180 grain bullets of the same type from the same length barrel. Zero a .300 WSM rifle shooting a 180 grain bullet (BC of .483) at 2970 fps for its maximum point blank range (+/- 3") and its trajectory will look like this: +2.6" at 100 yards, +3" at 150 yards, +2.2" at 200 yards, and -3" at 300 yards.
Velocity loss in barrels shorter than 24" is considerable. Chronograph results I saw showed that 180 grain factory loads lost about 50 fps of MV for each inch the barrel length was reduced.
Nosler figures for the .300 WSM show that 61.0 grains of IMR 4350 powder will drive their 180 grain bullets to a MV of 2861 fps, and 65.0 grains of the same powder will give a MV of 3024 fps. Nosler used Winchester brass and primers for these loads. Note, however, that these figures were developed in a 26" test barrel.
The .300 WSM has generated a lot of interest in the firearms press. Already Winchester has introduced a .270 WSM and a 7mm WSM, both based on a necked down .300 WSM case.
I have tried to point out the disadvantages of the .300 Winchester Short Magnum as well as its advantages because most of the firearms press, in their excitement to promote something new, has not been inclined to report the entire truth about the limitations of the new cartridge. These drawbacks are something that shooters should understand before purchasing a .300 WSM rifle.
It has been my hope that the interest generated by the introduction of the .300 WSM and its offspring would spur a revival of two earlier and better balanced short magnums, the 6.5mm and .350 Remington Magnums. These cartridges were far ahead of their time when they were introduced in the middle 1960's. In 2003 Remington announced the reintroduction of the .350 Magnum, along with a new Model 673 Guide Rifle in which to shoot it. Perhaps the day of the true short magnum cartridge has come at last.
Copyright 2003, 2012 by Chuck Hawks. All rights reserved.