The .270 WSM
By Chuck Hawks
This is the most useful of the WSM line of cartridges. Unlike the other WSMs, the .270 does not simply duplicate the ballistics of an existing cartridge. The .270 WSM and the .300 WSM are the most successful and popular of the short magnum rifle cartridges and the most widely available in terms of both ammunition and rifles.
The advertised ballistics of the .270 WSM (Winchester Short Magnum) fall 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. The muzzle energy of this load is 3,096 ft. lbs., and at 300 yards 1964 ft. lbs. of energy remains. Clearly, the .270 WSM will make an exemplary long range cartridge and it is suitable for consideration as an all-around caliber for thin skinned game.
Here are some specifications of interest to .270 WSM reloaders: bullet diameter .277", maximum COL 2.86", maximum case length 2.10".
There is a very good selection of bullets in .270 caliber, ranging from about 90-180 grains. Like any .270 Magnum, the WSM version has too much powder capacity for the light 90-120 grain bullets. And the short case of the WSM calibers works against the heaviest (long) bullets. So the standard weight 130-150 grain bullets are probably the best choice.
Medium to slow burning propellants are the usually selected for the .270 WSM. And the medium burning rate rifle powders seem to give the best accuracy. Reasonable powders include AA-3100, H4350, IMR 4350, and RL-19.
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. IMR 4350 was the most accurate powder tested with this bullet weight.
For Nosler's 140 grain bullets 56.5 grains of IMR 4350 gives a MV of 2938 fps, and a maximum load of 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 the 160 grain Nosler Partition Semi-Spitzer. This bullet has a sectional density of .298 and is shorter than a spitzer bullet of the same weight. 56.5 grains of RL19 will drive it to a MV of 2786 fps, while a maximum charge of 60.5 grains of RL19 will yield a MV of 2975 fps. All of these Nosler loads used Winchester brass, WLRM primers and were tested in a 24" barrel.
Note: A full length article about the .270 WSM can be found on the Rifle Cartridges page.
Copyright 2004, 2016 by Chuck Hawks. All rights reserved.