The 7mm WSM and 7mm Rem. Short Action Ultra Mag
By Chuck Hawks
Remington and Winchester went to short, fat, unbelted cases for their latest 7mm magnums, the 7mm Remington Short Action Ultra Mag and the Winchester Short Magnum. Both cartridges were designed to work through short action rifles. Both were introduced in 2001.
The marketing of these cartridges is designed promote their use in lightweight mountain rifles. This is an idea that has considerably more appeal to those who have never fired a magnum cartridge in a carbine length rifle than to those who have.
The Remington version is based on the same case as the .300 SAUM, necked down to handle .284" bullets. The SAUM cartridges are based on the long .300 Ultra Mag case, drastically shortened to work in special Magnum versions of the Model 7 rifle, which weigh between 6.125 and 7.25 pounds and sport 22 inch barrels.
Winchester's 7mm WSM is based on the .300 WSM case necked down to handle .284" bullets. It was initially introduced in a 7.5 pound version of the Model 70 Featherweight rifle with a 24 inch barrel as well as other short action Winchester and Browning models. The latter weigh 6 pounds 9 ounces and are supplied with 23 inch barrels.
Both the Remington and Winchester short magnums have a rebated rim so that they can be used with existing magnum bolt faces. The powder capacity of the two cases is similar, and their powder capacity is also similar to that of the very popular 7mm Remington Magnum.
Remington claims that the ballistics of the 7mm SAUM equal those of the popular 7mm Rem. Mag., and exactly the same claim is made for the 7mm WSM. These claims are valid if the short magnum cartridges are fired in 24 inch barrels, the same length as the barrels of most 7mm Rem. Mag. rifles. In shorter barrels, performance declines dramatically.
Winchester claims a muzzle velocity (MV) of 3,225 fps with a 140 grain bullet for their 7mm WSM cartridge; the claimed muzzle energy (ME) is 3,233 ft. lbs. With a 160 grain bullet the Winchester figures are 2990 fps and 3176 ft. lbs. at the muzzle. The lighter, shorter 7mm bullets are preferred in these short case magnums.
Remington claims a MV of 3175 fps and ME of 3133 ft. lbs. for their 7mm SAUM with a 140 grain bullet. With a 160 grain bullet the Remington figures are 2960 fps and 3112 ft. lbs. at the muzzle. All of the figures from both companies were developed in 24 inch test barrels.
Shooting Times magazine chronographed Remington factory loads for the 7mm SAUM in a Model 7 rifle's 22 inch barrel and got instrumental velocities of 3,055 fps for the 140 grain bullet and 2,795 fps for the 160 grain bullet. It is worth noting that a rifle with the same length barrel chambered for the standard .280 Remington cartridge can duplicate these velocities. The greatly reduced velocity with the 160 grain bullet as chronographed by Shooting Times is probably a result of the longer bullet protruding too far into the powder space of the stubby case, as well as the short (for a magnum) 22 inch barrel.
This points out the greatest advantage of the standard length 7mm Rem. Mag. and 7mm Wby. Mag., which can efficiently handle the heavy 160 and 175 grain bullets most suitable for shooting large animals such as elk, moose, and grizzly bear. Anyone purchasing a 7mm Magnum rifle for hunting large animals would do well to avoid the short magnums.
In rifles with barrels long enough and loads hot enough to achieve a muzzle velocity of 3175 fps with a 140 grain bullet, either short magnum will have a trajectory similar to that of the standard length 7mm Rem. Magnum. Zero a scoped rifle so that a Nosler Partition bullet hits 3 inches high at 100 yards, and it should strike about 3.4 inches high at 200 yards, 0.7 inch low at 300 yards, and 10.2 inches low at 400 yards. This makes the 7mm WSM and 7mm SAUM about 330-340 yard deer and antelope rifles.
From a scoped rifle zeroed to hit 3 inches high at 100 yards, a 160 grain Nosler Partition bullet at 2900 fps will hit about 2.9" high at 200 yards, 2.7 inches low at 300 yards, and 14.7 inches low at 400 yards. This will allow a good shot to take elk out to about 325 yards without worrying too much about bullet drop.
Reloading data published in the fifth edition of the Nosler Reloading Guide for the 7mm Rem. SAUM shows that 56.0 grains of IMR 4350 powder will drive their 140 grain bullets to a MV of 2943 fps, and 60.0 grains of IMR 4350 is good for a MV of 3146 fps. IMR 4350 was the most accurate powder tested. The Nosler loads were developed in Remington cases with Remington primers, and chronographed in a 24 inch barrel.
Hodgdon reloading data for the 7mm WSM shows that the 140 grain Nosler Partition spitzer bullet can be driven to a MV of 2979 fps in front of 58.0 grains of H4350 powder. The maximum load for that bullet is 61.5 grains of H4350 powder, which yields a MV of 3133 fps at a chamber pressure of 61,900 psi. The Hodgdon technicians used Winchester cases and primers to develop their loads, and they were chronographed in a 24 inch barrel.
Needless to say, when either of these cartridges is fired in a light weight, short barreled rifle the recoil is unpleasant and the muzzle blast is severe. Weatherby, who knows a thing or two about magnum rifles, supplies 26" barrels with all Mark V rifles chambered for their Big 7. A range session with any 7mm Magnum cartridge in a carbine length rifle will confirm the wisdom of this policy. However, there can be no doubt that such rifles pack a fearsome punch in a compact package.
Copyright 2001, 2012 by Chuck Hawks. All rights reserved.