The .270 WSM (Winchester Short Magnum)
By Chuck Hawks
The .270 WSM was introduced in 2001. It is designed to give magnum performance in a .27 caliber cartridge that will work through a short action rifle. The .284 Win. and 6.5mm Rem. Mag., introduced in the 1960's, were attempts to equal .270 Win. ballistics in a fat, stubby cartridge designed to work in short action rifles, but both were commercial failures. The new .270 WSM is the latest attempt to bring .270 magic to short action rifles.
Unlike those earlier cartridges, the .270 WSM is a real .270, and uses standard diameter .277" bullets. It is based on the very fat .300 WSM case necked down. The body of this case is so fat (.555 inch) that the magnum size .535 inch rim must be rebated (made smaller in diameter than the cartridge body) to allow the cartridge to work with a magnum size bolt face. The case length is 2.1 inches, and the overall cartridge length is 2.86 inches. The shoulder angle is a very sharp 35 degrees. Magazine capacity is reduced by one round compared to standard diameter magnum cartridges like the 7mm Remington Magnum.
The rebated rim and sharp shoulder could potentially cause feeding problems. When coupled with the reduced magazine capacity, this mitigates against using the .270 WSM on any animal that could be considered dangerous, although the cartridge has adequate power for the smaller, thin-skinned, dangerous species. (Note Murphy's Law!)
This ultra fat short magnum not only equals .270 Win. performance, it exceeds it. The ballistics of the .270 WSM falls between the ballistics of the standard .270 Win. and the powerful .270 Weatherby Magnum. Winchester factory ballistics quote a muzzle velocity of 3275 fps for the .270 WSM shooting a 130 grain Ballistic Silvertip bullet in a 24 inch barrel. This exceeds Winchester's .270 Win. factory load with the same bullet by 225 fps (also measured in a 24 inch barrel), and comes within 100 fps of Weatherby's 130 grain load for their .270 Wby. Mag. (as measured in a 26 inch barrel). The muzzle energy of this load is 3,096 ft. lbs., and at 300 yards 1964 ft. lbs. of energy remains (Winchester figures). Clearly, the .270 WSM will make an exemplary long range cartridge, and is suitable for consideration as an all-around caliber for non-dangerous game.
Zero a scoped .270 WSM rifle to hit 2.5 inches high at 100 yards with a 140 grain spitzer bullet and the .270 WSM is about a 306 yard medium game cartridge. The midrange rise will be about 3 inches, and the maximum point blank range is about 306 yards, where the bullet will hit about 3 inches low. This is almost identical to the trajectory of the standard .270 Winchester with a 130 grain bullet.
The 130 grain bullet is probably the best choice for the smaller species of antelope, deer, sheep, and goats. The 140 grain bullet would be a good choice for a mixed bag hunt, and a premium controlled expansion 150 grain bullet is probably the best choice for shooting large game. The Optimal Range Table shows that shooting an appropriate 150 grain bullet the .270 WSM is adequate for 600 pound animals out to 275 yards. Accuracy with all bullet weights is reported to be very good.
The .270 WSM is an easy cartridge for which to reload. It thrives on slow burning powders like #4350, #4831, and RL19. Reloaders can duplicate the factory load velocities in a 24 inch barrel with all bullet weights, but not exceed them by much. The factory loads represent maximum loads in the .270 WSM. All of the Nosler reloads that follow used Winchester brass and primers.
The fifth edition of the Nosler Reloading Guide shows that 59.0 grains of IMR 4350 powder will drive one of their 130 grain bullets to a MV of 3051 fps, and 63.0 grains of the same powder will give a 130 grain bullet a MV of 3294 fps. For Nosler's 140 grain bullets 56.5 grains of IMR 4350 gives a MV of 2938 fps, and 60.5 grains of IMR 4350 is good for a MV of 3154 fps. For 150 grain bullets the Nosler figures are 54.0 grains of IMR 4350 for a MV of 2813 fps, and up to 58.0 grains of the same powder for a MV of 2992 fps.
Reloaders also have access to bullet weights not available in factory loads, such as the 160 grain Nosler Partition Semi-Spitzer. This bullet has a sectional density of .298. 56.5 grains of RL19 will drive it to a MV of 2786 fps, while 60.5 grains of RL19 will yield a MV of 2975 fps. This makes the 160 grain partition an interesting possibility for large game like elk.
Like all magnums, the .270 WSM needs a long barrel to burn the large volume of powder contained in its fat hull. A 26 inch barrel will give the best performance, and any barrel shorter than 24 inches is going to seriously reduce performance. But long barrels tend to negate the advantages of a short action, which is a problem faced by all of the new short magnum calibers. In the carbine length mountain rifles that would seem to be their natural home, performance falls dramatically. In rifles with 22 inch or shorter barrels, the result is terrific muzzle blast for little or no advantage over standard calibers.
The other factor that must be considered is recoil. In an 8 pound rifle, recoil is 18.7 ft. lbs. shooting a 130 grain bullet at a MV of 3266 fps., or about 14% greater than with a standard .270 Winchester rifle. Naturally, if rifle weight is reduced to take advantage of the cartridge's short action capability, recoil will increase. The recoil and blast of a magnum cartridge in short barreled carbine length rifle would make a cigar store's wooden Indian flinch! On the other hand, for those accustomed to magnum recoil, the .270 WSM is no worse than many other magnum cartridges, and better than most.
Copyright 2001, 2012 by Chuck Hawks. All rights reserved.