The .357 SIG is based on a necked-down .40 S&W case. Any pistol chambered for the .40 S&W can be adapted to the .357 SIG and several are. Buyers of pistols chambered for the two cartridges will have to decide which cartridge best fits their needs, so comparison of the two cartridges is inevitable.

The .357 SIG

The .357 SIG was developed in 1994 by Federal Cartridge and SIG Arms. Like many other cartridges, it is misnamed, as it actually uses .355 inch (9mm) bullets, not the true .357 inch bullets of the .357 Magnum and .38 Special.

The .357 SIG is based on a necked-down and slightly lengthened .40 S&W case with zero body taper and a small 18-degree shoulder. The maximum case length is specified as 0.865 inch and the maximum cartridge overall length is 1.140 inches. The .357 SIG operates at a high maximum average pressure (MAP) of 40,000 psi, which is very high for an auto pistol cartridge. For comparison, the 9mm Luger and .40 S&W operate at 35,000 psi MAP.

Unfortunately, the .357 SIG headspaces on its case mouth, like a conventional straight case auto pistol cartridge, not on the shoulder of the case, like most bottleneck cartridges. This is important to note, because it means reloaders cannot simply neck down .40 S&W cases to create .357 SIG cases--they turn out to be .01-.02 inch short. Use only actual .357 SIG brass for reloading.

The feed reliability of the .357 SIG cartridge is very good, due to its rimless bottleneck configuration. The .355 inch bullet funnels easily into a chamber reamed to accept the 0.424 inch body diameter of the cartridge.

The cartridge has not set the world on fire, but it has become reasonably popular. Factory loaded ammunition is available from Federal, Hornady, Remington, Speer, Winchester and others. Although .357 SIG factory loads are offered by various of the Big 4 US ammo makers (Remington, Winchester, Federal and Hornady) with 105, 125, 135 and 147 grain bullets, by far the most common bullet weight is 125 grains, usually in the form of a FMJ or JHP bullet.

The .40 S&W

Winchester designed the .40 S&W, which was introduced in 1990. The basic idea was to duplicate the ballistics of the light (FBI) 10mm Auto load in a cartridge that could be adapted to medium frame autoloaders designed for the popular 9mm Luger cartridge. Smith & Wesson realized that for police or self-defense purposes the large powder capacity of the 10mm Auto was wasted and the drawbacks of a large frame pistol (required for the 10mm) could be avoided if the new cartridge could be made small enough to work in 9mm pistols.

The .40 S&W is based on a 10mm Auto case shortened to .850 inch long. It uses the same .400 inch diameter bullets as the 10mm Auto. By reducing the powder space to only that needed to duplicate the 10mm Lite police load, the case was held to the same overall length as the 9x19. The .40 uses a true straight case. It is not tapered for feed reliability like the 9x19 case. The SAAMI maximum average pressure is 35,000 psi.

The .40 S&W successfully met all of its design parameters and was an immediate success. It has become the most popular police service cartridge in the US. All of the major auto pistol manufacturers offer guns in .40 S&W and all of the major ammunition companies load .40 S&W cartridges. The sales of reloading dies in the caliber is also strong.

Factory loads from the Big 4 are offered with bullets weighing 135, 140, 155, 165, 175 and 180 grains. 165 and 180 grains are, by far, the the most popular bullet weights. Of the two, 165 grains is considered the best stopper, according to Marshall and Sanow.

The Comparison

To keep things as uniform as possible, we will use Remington factory loads for comparison. These are typical SAAMI loads and standard ballistics are provided by Remington. Specifically, we will compare the 125 grain JHP load in .357 SIG (#L357S2) and 165 grain brass JHP load in .40 S&W (#GS40SWA).

We will compare the .357 SIG and .40 S&W in velocity, energy, trajectory, bullet diameter, sectional density (SD) and recoil. At the end of the comparison will be a brief summary and conclusion.

Velocity

Velocity is important for initiating bullet expansion and it is the most important factor in calculating kinetic energy. Higher velocity flattens trajectory, making hitting easier at extended ranges and unknown ranges. SAAMI standard velocities for both the .357 SIG and .40 S&W are taken in 4.0 inch barrels. Here are the Remington published velocities in feet per second (fps) of our comparison loads at the muzzle (MV), 25 yards and 50 yards.

• .357 SIG, 125 grain: 1350 fps MV, 1157 fps at 25 yards, 1032 fps at 50 yards
• 40 S&W, 165 grain: 1150 fps MV, 1040 fps at 25 yards, 964 fps at 50 yards

Not surprisingly, given its lighter bullet, the .357 SIG has a 200 fps velocity advantage at the muzzle. It wins the velocity comparison at all ranges and this bodes well for its trajectory.

Energy

Kinetic energy is defined as the ability to do work; in this case, powering bullet penetration and expansion. Both are, of course, necessary for lethality. It is also worth noting that kinetic energy is a reasonably good indicator of potential effectiveness when comparing similar cartridges shooting similar bullets. Here are the Remington energy figures in foot-pounds (ft. lbs.) for our comparison loads at the muzzle (ME), 50 yards and 100 yards.

• .357 SIG, 125 grain: 506 ft. lbs. ME, 372 ft. lbs. at 50 yards, 296 ft. lbs. at 100 yards
• .40 S&W, 165 grain: 485 ft. lbs. ME, 396 ft. lbs. at 50 yards, 340 ft. lbs. at 100 yards

At the muzzle the .357 SIG has a 21 ft. lb. advantage over the .40 S&W, but at 50 yards the situation is reversed, with the .40 S&W enjoying a 24 ft. lb. advantage. At 100 yards, the .40's advantage increases to 44 ft. lbs. Service pistols are generally considered most suitable for use at relatively short range and are typically zeroed at 25 yards, where the .357 SIG and .40 S&W are about equal in kinetic energy.

Trajectory

Trajectory is not as important for a police service or personal defense cartridge as it is for a handgun hunting cartridge, as most defensive shooting scenarios take place at short range, less than seven yards. However, not all bad guys are encountered at near contact range and some folks carry their service caliber autos for protection from two legged predators in the field.

Without question, a flatter trajectory makes hitting easier as the range increases and delays the need to "hold over" to hit the target. Mid-range trajectory (MRT) shows the maximum bullet rise above the line of sight between the muzzle and the distance at which a gun is zeroed. Here are the mid-range trajectories for both cartridges at 50 and 100 yards.

• .357 SIG, 125 grain: +0.7 inches MRT at 50 yards, +3.2 inches MRT at 100 yards
• .40 S&W, 165 grain: +1.0 inches MRT at 50 yards, +4.0 inches MRT at 100 yards

While the difference is not great, the .357 SIG is clearly the flatter shooting cartridge.

Bullet Diameter

Bullet diameter determines cross-sectional area. Given an equal percentage of bullet expansion, a larger diameter bullet will create a wider wound cavity, destroying more tissue, other factors being equal. Here are the actual bullet diameters of our two cartridges.

• .357 SIG: .355 inch
• .40 S&W: .400 inch

Since we are comparing cartridges using the same basic case, but different bullet diameters, it was a forgone conclusion that the .40 S&W would win the comparison in bullet diameter.

Sectional Density

Sectional Density is the ratio of a bullet's weight (in pounds) to its diameter squared (in inches). SD is important when comparing cartridges and loads because, other factors (such as impact velocity and bullet expansion) being equal, the bullet with the greatest SD will penetrate deeper, creating a longer wound cavity and increasing tissue destruction.

Superior SD also improves the penetration of barrier materials, giving the bullet a better chance to reach a target on the other side (again, other factors being equal). Remember, the actual bullet diameter of the .357 SIG bullet is .355 inches and the actual bullet diameter of the .40 S&W is .400 inches.

• .357 SIG, 125 grain: .142 SD
• .40 S&W, 165 grain: .147 SD

The difference in sectional density is not great and both are adequate for use against unarmored human beings. Nevertheless, a .400/165 grain bullet should have a slight advantage in penetration over a .355/125 grain bullet, other factors being the same.

Recoil

Recoil is a bad thing, as it distracts the shooter, leads to flinching and degrades accuracy. Anyone can shoot better with a pistol that kicks less.

The most popular full size .40 S&W service pistol in police (and probably civilian) use is the Glock 22. The G22 weighs approximately 2.13 pounds with a loaded magazine (15 rounds). It is hard to say what is the most popular .357 SIG service pistol, but the full size Glock 31 must be right up there. The G31 weighs approximately 2.07 pounds with a loaded magazine (15 rounds). For calculating the recoil of our comparison loads, we will use two pounds as a standard pistol weight.

• .357 SIG, 125 grain at 1350 fps, 2 lb. pistol: 6.5 ft. lbs. recoil energy, 14.5 fps recoil velocity
• .40 S&W, 165 grain at 1150 fps, 2 lb. pistol: 7.8 ft. lbs. recoil energy, 15.8 fps recoil velocity

Both cartridges generate a sharp muzzle blast and rather sharp recoil pulse, as you can see from the recoil velocity figures. However, the .357 SIG wins the recoil comparison.

Summary and Conclusion

The .357 SIG wins this comparison in the velocity, trajectory and recoil categories. The .40 S&W wins in the bullet diameter and sectional density categories. Energy is about equal at 25 yards, the most common zero distance for both calibers.

The .357 SIG and .40 S&W are good choices for self-defense in urban and suburban settings. Both cartridges offer the possibility of good stopping power with appropriate bullets. They have more muzzle blast and kick harder than the ubiquitous 9mm Luger (9x19mm) autoloading pistol cartridge, but they can be controlled by reasonably experienced shooters.

The selection of both guns and ammunition is significantly better in .40 S&W and .40 S&W ammo is more widely distributed. This gives the .40 a considerable advantage for many shooters and is probably the single greatest practical difference between the two calibers.