The .25 WSSM
By Chuck Hawks
The new for 2004 .25 WSSM came as something of a surprise to many, as it was widely supposed that Winchester (Olin) would base a new .257 Magnum on the longer WSM case. Rumor has it that they tried, but found that the resulting cartridge had an erratic pressure curve and was very touchy to reload. The decision was made to base the new .25 caliber cartridge on the WSSM case instead.
This so reduced powder capacity that it became impossible to endow the new .25 WSSM cartridge with true magnum performance. The result is a new cartridge with nearly identical performance to the old .257 Roberts Improved wildcat cartridge. Although the .25 WSSM is advertised as ballistically equivalent to the .25-06, it is clearly inferior if the two cartridges are loaded to similar pressures and tested in rifles with barrels of the same length.
Winchester Ammunition's 2004 Product Guide lists three factory loads for the .25 WSSM. These include an 85 grain Ballistic Silvertip bullet at a MV of 3470 fps and ME of 2273 ft. lbs., a 115 grain Ballistic Silvertip bullet at a MV of 3060 fps and ME of 2392 ft. lbs., and a 120 grain Positive Expanding Point bullet at a MV of 2990 fps and ME of 2383 ft. lbs.
The 85 grain bullet is for shooting varmints (CXP1 class animals). The 115 grain bullet is intended for light CXP2 class animals no larger than deer. And the 120 grain bullet should be the best choice for general CXP2 class game hunting (antelope, deer, mountain goats, sheep, and black bear).
Winchester based the .25 WSSM on the .243 WSSM case, giving the new cartridge a 30 degree shoulder angle to slightly increase powder capacity. The rebated rim has a standard magnum diameter of .535" and the bloated body a head diameter of .555". Case length is 1.670" and cartridge overall length is held to 2.360" so that it will work in the same actions as the previous .223 and .243 WSSM cartridges. Bullet diameter is .257".
According to data published by the Hodgdon Powder Company, an 87 grain Sierra soft point bullet in front of 40.0 grains of VARGET powder achieves a MV of 3198 fps. The same bullet in front of 44.0 grains of VARGET can be driven to a MV of 3434 fps (at a MAP of 62,600 psi).
Hodgdon figures also show that the 100 grain Speer BT bullet can be driven to a MV of 3022 fps by 39.0 grains of VARGET, and to a MV of 3248 fps by a maximum load of 42.8 grains of VARGET (at a MAP of 62,700psi).
Lastly, a 120 grain Swift spitzer bullet can be driven to a MV of 2793 fps by 42.0 grains of H4350 powder. 45.5 grains of H4350 will drive the same bullet to a MV of 2981 fps (at a MAP of 62,400 psi!), very close to the factory load ballistics.
These Hodgdon loads were assembled using Winchester cases and WLR primers. They were derived in a 24" test barrel, so remember to subtract about 150 fps if you are shooting a regular production .25 WSSM hunting rifle.
Note: A full length article about the .25 WSSM can be found on the Rifle Cartridge Page.
Copyright 2004, 2012 by Chuck Hawks. All rights reserved.