Compared: The .357 Magnum and .357 SIG

By Chuck Hawks

The .357 Magnum was the original magnum revolver cartridge. It was introduced by Smith & Wesson in 1935. It is one of the all-time best selling cartridges, widely used for both handgun hunting and personal defense. It has also been adapted to rifles.

The .357 Magnum has become the standard of comparison among personal defense handgun cartridges, with the highest percentage of one shot stops of any handgun cartridge. Almost every revolver that can stand the pressure is chambered for the .357 Magnum. There are small frame, medium frame, and large frame .357 revolvers. It is also one of the most popular calibers in single shot pistols, and even some autoloading pistols have been adapted to the cartridge, making for an extensive choice of guns in the caliber.

For most of its life, the standard .357 Magnum factory load has driven a 158 grain cast or jacketed bullet of .357" diameter at a muzzle velocity (MV) of 1550 fps from an 8 3/8" barrel (Remington figures). Because the .357 was loaded to full pressure, this velocity figure was pretty close, and was verified by independent chronograph tests (including mine). More recently, in this the age of the tort lawyer, the SAAMI maximum average pressure (MAP) of the .357 Magnum has been reduced to 35,000 psi. The factory loaded 158 grain bullet now has a catalog MV of approximately 1240 fps and muzzle energy (ME) of 535 ft. lbs. as measured in a 4" vented barrel (revolver barrel).

Other bullet weights from 95 grains to 200 grains are offered, but today's hot factory load for the .357 is a 125 JHP bullet at a MV of about 1450 fps and ME of 583 ft. lbs. from a 4" vented barrel (again these are Remington figures). I have checked the velocity of this factory load from a 4" Python revolver on my chronograph and found it to be quite accurate.

The .357 SIG cartridge was introduced in 1994 by Federal and SIG Arms for the fine SIG semi-automatic service pistols (P226, P229, and P239). It is worth noting that while the nomenclature of the .357 SIG intentionally implies that it is a .357 caliber, this is not the case. It is actually a 9mm auto pistol cartridge and takes standard diameter 9mm (.355") bullets.

The .357 SIG is advertised as providing .357 Magnum ballistics in a semi-automatic pistol, although (as we shall see) that is not literally true. It is, however, a relatively powerful cartridge adaptable to any semi-automatic pistol chambered for the .40 S&W cartridge. The .357 SIG actually offers ballistics about midway between the .38 Super Automatic and the .357 Magnum. In addition to SIG, as this is written, Glock and H&K offer pistols in .357 SIG caliber.

The original Federal .357 SIG factory load claimed to drive a 125 grain jacketed bullet at a MV of 1350 fps with ME of 510 ft. lbs. from a 4" barrel (with a sealed breech, not vented). I have not been able to verify the accuracy of these figures, but I have read that they are reasonably close. This remains the standard and most practical load for the caliber, although 147 and 150 grain bullets are available. .357 SIG cartridges are factory loaded by several of the U.S. ammunition manufacturers, although the selection of offerings is considerably less than for the .357 Magnum.

The .357 Magnum is a rimmed case based on the .38 Special case lengthened by .135" to increase powder capacity. This also serves to eliminate the possibility of high pressure .357 cartridges being fired in low pressure .38 Special revolvers. On the other hand, all .38 Special cartridges may be used in any .357 revolver, further increasing the flexibility of the caliber.

The .357 SIG is based on a necked-down .40 S&W case with an 18 degree shoulder. This makes for a very stubby bottleneck case, but the .357 SIG headspaces on the case mouth, just like most straight case auto pistol cartridges, not the shoulder.

It should be obvious to any experienced shooter that there is no practical difference in frontal area between bullets of .355" and .357" diameter. .002" more or less in bullet diameter is just not enough to matter. Other factors, such as bullet design and impact velocity, are far more important.

If .357 Magnum and .357 SIG bullets of the same weight and identical design are fired from at the same velocity, the kinetic energy and penetration will be equal. However, when comparing the ballistics of the .357 Magnum and .357 SIG, things are not equal.

Loaded to the maximum permissible pressure the .357 Magnum will outperform the .357 SIG because its case has greater powder capacity. This is why, even with the disadvantage of being tested in a vented barrel, the standard 125 grain .357 Magnum factory load has a 100 fps advantage in MV and 70 ft. lbs. advantage in ME over the .357 SIG. If the .357 Magnum load were chronographed in a 6" barrel, the standard and most common barrel length for magnum revolvers, its advantage would be even greater.

Because of its higher velocity the .357 Magnum also shoots a little flatter than the .357 SIG. For example, comparing Federal factory loads using 125 grain JHP bullets in both calibers, the .357 Magnum bullet has a 100 yard mid-range trajectory of 2.8" and the .357 SIG has a 100 yard mid-range trajectory of 3.1".

Because of its superior ballistics and greater variety of loads, including .38 Special loads, a .357 Magnum handgun is a much more versatile choice for the recreational shooter or handgun hunter. It can properly be used for plinking, target shooting, small game hunting, and medium size big game hunting. A .357 Magnum revolver is also a good "insurance policy" when camping, fishing, or hiking afield. Also, many fine revolvers and single shot pistols designed for the hunter and recreational shooter are available in .357 Magnum caliber.

The .357 SIG, as a service auto pistol cartridge, lacks the accuracy for target shooting or small game hunting. It lacks the bullet weight and sectional density for big game hunting or serious protection against large predators afield. And it cannot be loaded down far enough to make it a comfortable plinking cartridge. In addition, there are no hunting or target type pistols chambered for the cartridge. The .357 SIG is not a good choice as a multi-purpose cartridge for the recreational shooter.

The shooter relying on factory loads will find a much greater variety and availability of loads for the .357 Magnum. Because it is among the best selling of all handgun cartridges, .357 Magnum factory loads are much more widely distributed than .357 SIG factory loads. For example, the 2003 edition of the Shooter's Bible lists 47 individual factory loads from 9 manufacturers for the .357 Magnum, compared to only 15 individual loads from 6 manufacturers for the .357 SIG.

For the reloader, the availability of bullets and brass is important. In this area the .357 Magnum also has a big advantage. Because of the Magnum's popularity, nearly all bullet makers offer a wide selection of .357" diameter bullets. These typically range for 95 grains to 200 grains. Brass is in plentiful supply from virtually all manufacturers. In addition, of course, .38 Special brass and components may be used. Because of its large, straight, rimmed case the .357 Magnum is an easy cartridge to reload. And because revolvers do not depend on the recoil momentum of the cartridge to operate, handloads can range from the lightest .38 Special target loads to full throttle magnum loads, a velocity range of approximately 600 fps to 1500 fps.

The .357 SIG offers nothing comparable to reloaders. In fact, it is a somewhat unusual pistol cartridge to reload. Brass is available, but not particularly plentiful. Care must be taken during the resizing operation due to its bottleneck case form. Bullets may not be roll crimped because the case headspaces on the case mouth instead of the shoulder or rim. .40 S&W brass should not be reformed into .357 SIG brass; the resulting cases are too short to maintain proper headspace. Bullet diameter is the same as other 9mm pistol cartridges, but not all 9mm bullets are suitable for use in the .357 SIG. In particular, the NATO style 9x19 FMJ bullets may not be used. Their taper is such that not enough bearing surface contacts the short neck of the .357 SIG case. That is why Speer makes special 125 and 147 grain bullets specifically for the .357 SIG. As with any semi-automatic pistol cartridge, reloads must not vary far from factory load velocities or the gun may jam. And autoloading pistols throw their brass all over the place, making recovery difficult and time consuming.

As alluded to earlier, the .357 Magnum's popularity also carries over into the availability of guns. Virtually every gun maker who builds a suitable handgun chambers it for the .357 Magnum cartridge. The selection of pistols in .357 SIG caliber is much smaller.

The "Handgun Recoil Table" shows that a typical .357 Magnum revolver shooting a 125 grain bullet at a MV of 1450 fps develops 7.1 ft. lbs. of recoil energy and a recoil velocity of 13 fps. A typical .357 SIG semi-auto shooting a 125 grain bullet at a MV of 1350 fps develops 7.4 ft. lbs. of recoil energy and a recoil velocity of 16.6 fps. The less powerful .357 SIG cartridge develops more recoil because its pistol is lighter. In guns of equal weight the .357 Magnum would kick more. In practical terms, the difference in recoil is probably not enough to matter to most shooters. Neither is particularly pleasant to shoot compared to, say, an ordinary .38 Special revolver. In addition, both .357's have substantial muzzle blast.

I would summarize the .357 Magnum vs. .357 SIG comparison thusly. The ballistics of the .357 Magnum are somewhat superior, and for self defense its stopping power is unexcelled. It is also a much more versatile cartridge for the recreational shooter and handgun hunter. In terms of recoil there is little to choose between the two. For a revolver or single shot pistol the .357 Magnum is the natural, and superior, choice.

If you are starting fresh, with no commitment to either cartridge or type of gun, the .357 Magnum is probably the better, more versatile, choice. There is more factory loaded ammunition and more guns (new and used) available in .357 Magnum. .357 Magnum ammunition is also more likely to be on sale. If you are a reloader the .357 Magnum is again the superior choice. If you later wish to sell your gun, you will find a larger market for a .357 Magnum than for a .357 SIG.

The .357 SIG is inferior to the .357 Magnum in almost every way, except one. If you are looking for a powerful, flat shooting, semi-automatic service pistol the .357 SIG cartridge is worth considering. SIG, Glock, and H&K autoloading pistols are fine examples of the type, and they are not available in .357 Magnum caliber.

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Copyright 2003, 2012 by Chuck Hawks. All rights reserved.