The 7mm STW (Shooting Times Westerner)
By Chuck Hawks
The 7mm STW has the honor of being (as far as I know) the first cartridge named for a gun magazine. STW stands for "Shooting Times Westerner," the same Shooting Times magazine to which many North American shooters subscribe or buy off the rack.
The 7mm STW was designed by Layne Simpson, Field Editor of Shooting Times, in 1979. In the May 1989 issue of Shooting Times an article about the cartridge by Mr. Simpson appeared, and the rest is history.
For whatever reason, the 7mm STW (as Layne Simpson called his cartridge) caught the fancy of shooters in a way that the 8mm Remington Magnum (on which it is based) never has. The 7mm STW is one of those rare wildcats that became more successful than its parent cartridge. The powers that be at Remington certainly missed a good bet by not offering the cartridge themselves. This is the cartridge that should have become the 7mm Remington Ultra Mag.
In 1996 the 7mm STW was standardized by the SAAMI. A-Square was the first company to offer factory loaded ammunition in 7mm STW, and Federal, Remington, Speer, and Winchester have followed their lead.
The 7mm STW is based on an 8mm Rem. Mag. case necked down to accept standard .284" diameter bullets. It is easy to form 7mm STW cases by running 8mm Mag. cases through a 7mm STW resizing die. But, of course, this is no longer necessary as new 7mm STW brass is easier to find than 8mm Rem. Mag. brass, and factory loaded 7mm STW cartridges are more widely distributed than 8mm Mag. cartridges.
The 7mm STW case is a full (.300 H&H) length belted magnum case 2.85" long, and requires a magnum length action to accommodate it. Like the parent case, the 7mm STW case is 2.389" from the base of the rim to the bottom of the shoulder, and the very slight body taper is identical. The shoulder angle is also the same at 25 degrees. It is my understanding that the 7mm STW is loaded to the same 65,000 psi pressure limit as the 8mm Remington Magnum.
Factory loads give a 140-145 grain bullet a muzzle velocity (MV) of 3300-3450 fps, depending on brand. The 150 grain bullet is driven to 3250 fps, and the 160 grain bullet to 3150-3250 fps, again depending on brand. The A-Square loads claim the highest velocity with both the 140 and 160 grain bullets. All 7mm STW ballistics are developed in 26" test barrels, and shorter barrels will occasion a significant velocity loss.
Federal, who seems to occupy the middle ground in 7mm STW factory loads, claims a MV of 3330 fps and muzzle energy of 3435 ft. lbs. with a 140 grain Trophy Bonded bullet (SD .248). The 200 yard figures are 2850 fps and 2520 ft. lbs. This is probably the best bullet weight for medium size big game animals.
The Federal factory load drives the 150 grain Trophy Bonded bullet (SD .266) at a MV of 3250 fps with ME of 3520 ft. lbs. The 200 yard numbers are 2770 fps and 2565 ft. lbs. This is a good all-around bullet weight for the 7mm STW, as it is for most 7mm Magnum cartridges.
For large game, Federal loads a 160 grain Sierra Spitzer Boat-Tail bullet at a MV of 3200 fps with ME of 3640 ft. lbs. The 200 yard figures are 2850 fps and 2890 ft. lbs. The trajectory of this sleek bullet (BC .563, SD .283) is as follows (Sierra figures): +2.96" at 100 yards, +3.61" at 200 yards, 0 at 300 yards, and -8.45" at 400 yards. The 7mm STW is an excellent long range big game cartridge with this weight bullet.
Handloaders can approximately equal all of these velocities, and in addition have at their disposal 120, 125, 130, and 175 grain bullets. The lighter bullets would seem to be pointless in a case as large as the 7mm STW, but the 175 grain bullet (SD .310) might be called upon for use on the largest game, when exceptional penetration is called for.
According to the fifth edition of the Nosler Reloading Guide the 160 grain spitzer bullets can be given a MV of 2950 fps with 69.0 grains of RL22 powder, and a MV of 3121 fps with 73.0 grains of RL22. The 160 grain bullet hits harder than the 175 grain bullet at all ranges out to 400 yards. Remington cases and Federal 215 primers were used for these loads, which were chronographed in a 26" barrel.
The 7mm STW is one of the biggest and most powerful 7mm Magnums. Only the 7mm Remington Ultra Magnum can equal or marginally exceed its performance (at equivalent pressures), and even then only by burning considerably more powder and generating considerably more recoil. The 7mm STW probably represents the biggest practical 7mm Magnum. It seems that larger cases simply burn more powder to achieve a similar level of performance.
The price that must be paid for the 7mm STW's performance is, of course, recoil. An 8.5 pound 7mm STW rifle shooting a 160 grain bullet at 3185 fps belts the hapless shooter with 27.9 ft. lbs. of recoil energy. The 7mm STW is one of the new breed of super magnums that offer performance only a very few shooters can take advantage of and recoil an equally small number of shooters can tolerate.
Copyright 2002, 2012 by Chuck Hawks. All rights reserved.