The .25 WSSM
By Chuck Hawks
Winchester's big ammunition news for 2004 was the introduction of a third cartridge in their Winchester Super Short Magnum (WSSM) line. This new number takes standard .257" diameter bullets and is called the .25 WSSM. It is intended to duplicate the factory ballistics of the non-magnum .25-06, which has been around as a wildcat and later as a factory load for some 84 years. The point to the WSSM line is that they are extremely short cartridges, allowing the use of an action approximately 1/2" shorter than normal (.308 Win. length) short actions.
I do wish that Winchester had called their super short cartridges "Winchester Super Short Cartridge" and left off the "Magnum" tag. The term "magnum," as applied to rifle cartridges, connotes a larger than normal case, just as a magnum of champagne is a larger than normal bottle. Applying the magnum tag to a series of cartridges that are smaller than normal needlessly trashes the language and is essentially deceptive advertising.
At the Winchester display at the 2004 SHOT Show I was able to inspect both the ammunition and some of the rifles chambered for it. The less said about the Model 70 Super Shadow rifle the better, but the Model 70 Featherweight in .25 WSSM is a very cute and handy rifle, no doubt about it.
Unfortunately, the extra short action would be pointless with a 24" barrel, even though that is the length generally regarded as the minimum for magnum rifle cartridges and also the length of the test barrels Winchester Ammunition used to work up the factory ballistics for the .25 WSSM.
So the cute little Model 70's in .25 WSSM are supplied with a 22" barrels, and Browning A-Bolt rifles chambered for WSSM cartridges have barrels only 21" long. The upshot of all of this is that in the field the new .25 "Magnum" will actually be similar to the performance of the .257 Roberts +P. (Federal Premium ballistics specifies a 120 grain bullet at a MV of 2790 fps for the .257 +P.) Of course, the .257 Roberts is a perfectly good deer and antelope cartridge, and has been since the 1920's.
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).
I would expect the 120 grain load to be the most popular with big game hunters. For that load the Winchester ballistics table shows a remaining velocity at 200 yards of 2459 fps and energy of 1612 ft. lbs. At 300 yards the figures are 2216 fps and 1309 ft. lbs. The trajectory of that load looks like this: +1.6" at 100 yards, 0 at 200 yards, -2.9" at 250 yards, and -7.4" at 300 yards.
David M. Fortier, in the April 2004 edition of Shooting Times magazine, reported that he chronographed some 120 grain factory loads from the 22" barrel of a Winchester Model 70 and they actually averaged 2834 fps over the sky screens. That would mean a velocity loss of 156 fps and an actual kinetic energy of 2139 ft. lbs. Using those figures, here is the actual trajectory for that rifle and load: +2.7" at 100 yards, +3" at 130 yards, +1.6" at 200 yards, 0 at 232 yards, -3" at 273 yards, -5.8" at 300 yards, -20.8" at 400 yards. The maximum point blank range (+/- 3") for that load is 273 yards. For comparison, the MPBR for the .257 Roberts +P is 271 yards.
Winchester is making unprimed .25 WSSM brass available to reloaders in boxes of 50. It is obvious that Winchester has pushed the performance of the .25 WSSM as hard as it can be pushed. Winchester is using a non-canister ball powder that is not available to reloaders in their .25 WSSM factory loads. Experience with the .243 WSSM has shown that its peak pressure climbs very rapidly when approaching maximum loads, so reloaders working with the new .25 WSSM should approach maximum loads with more than the usual amount of caution.
According to data published by the Hodgdon Powder Company, and derived in a 24" test barrel (remember to subtract about 150 fps), a 120 grain SFT SP 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.
Winchester based the .25 WSSM on the .243 WSSM case, giving the new cartridge a slightly sharper 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.
The word within the industry is that Winchester first attempted, and would have preferred, to base a new .25 on the larger WSM case, which would have produced true magnum ballistics. Unfortunately, they found that the results using the larger case were unsatisfactory and the project was quietly dropped.
The main advantage the .25 WSSM has over the .243 WSSM is its ability to handle the heavy 120 grain bullet, which has a sectional density (SD) of .260. The heaviest bullet Winchester loads for the .243 WSSM weighs 100 grains and has a SD of .242. This should give the .25 the edge in penetration. Unfortunately, a 120 grain .257" bullet is about 1/8" longer than a 100 grain .243" bullet of similar design, so the .257 bullet protrudes deeper into the case, further reducing the powder capacity. Still, the .25 WSSM with its 120 grain bullet should be the most effective of the WSSM cartridges for hunting CXP2 class game. None of the WSSM cartridges should be used on larger CXP3 class game.
The basic very short, very fat shape of the WSSM cartridges, coupled with their rebated rim, makes them inherently less reliable than normal cartridges to feed from the box magazines of bolt action rifles. The advantages and disadvantages of the WSSM cartridge design have already been described in some detail in my articles about the .223 WSSM and .243 WSSM, so I will not go over the same material here. Many actions cannot be made to reliably cycle these cartridges, and some custom builders will not chamber for them.
Winchester and Browning have gone to great lengths to design new actions that will work with the WSSM cartridges, and success has not come easily or cheaply. I seriously suggest that anyone considering the purchase of a .25 WSSM rifle buy a Browning A-Bolt or Winchester Model 70 rather than having a custom rifle built on some other action.
Copyright 2004, 2012 by Chuck Hawks. All rights reserved.