357 SIG vs. 357 Mag: Clearing the Air on the 357!

The 357 SIG vs. 357 Mag debate has cooled down over the years, but it’s always worth considering which cartridge is better for self-defense. After all, the .357 SIG was designed to deliver performance equal to that of the .357 Magnum – plus function optimally in a semi-automatic.

This article compares the relative performance of the two cartridges, including their recoil, stopping power, accuracy, and overall cost. It’s all in service of helping you determine which round is better suited to your needs.

What’s the Difference Between 357 SIG and 357 Mag?

The greatest difference between these two rounds is the type of firearm they are designed for. The 357 SIG was created for semi-auto handguns, whereas the 357 Mag was intended for revolvers (though it was later adopted in lever-action rifles).

While these rounds are similar to one another, one may very well prove better than the other under certain conditions. Let’s begin by reviewing the differences in these cartridges’ specifications. We’ll then see how those differences impact real-world performance.

Cartridge Specifications

SIG Sauer designed the 357 SIG to emulate the 357 Mag’s performance. Despite this, they did not choose the 357 Mag as their new round’s parent case. They gave that honor to the 10mm Auto; an appropriate choice, given SIG’s goal of distilling big revolver energy into a semi-auto cartridge. (For reference, the much older 357 Mag’s parent case is the 38 Special.)

The 357 SIG is loaded with a 0.355” diameter bullet. True to its name, the 357 Mag fires a 0.357” diameter bullet. The neck diameter of the 357 SIG is 0.381”; the 357 Mag, 0.379”.

The 357 SIG has a larger base diameter than the 357 Mag: 0.424” and 0.379” 357 Mag, respectively. The 357 Mag has a longer case: 1.290”, which is 0.425” longer than the 357 SIG (0.865”). Its longer case gives the 357 Magnum an overall length of 1.590”. At 1.140”, the 357 SIG is a pipsqueak by comparison.

The 357 Mag’s longer case has more capacity: 26.2 grains H₂O, compared to 19.6 grains H₂O for the 357 SIG.

The 357 SIG’s maximum chamber pressure is higher: 40,000 psi, versus 35,000 psi for the 357 Mag.

Let’s see how these cartridges’ specs affect their real-world performance, beginning with how hard each one kicks.

Recoil: 357 SIG vs. 357 Magnum

I always compare recoil because it’s one of the first things a shooter asks about when firing a new cartridge. We all want to know how much the round kicks.

Many shooters fret about recoil – not so much because of physical pain (though this can be an issue), but more so for initial accuracy and follow-up shots. Compared to a cartridge with less recoil, one with more will kick the muzzle off the target more with each shot. This can slow follow-up shot placement, as well as cause the shooter to develop a flinch which further impairs marksmanship.

The less recoil you feel, the more accurately you can fire. Less recoil is always better (unless you’re a macho man who has to prove how tough you are to the world).

Felt recoil is subjective. It varies from shooter to shooter. That’s why I base my comparisons on free recoil energy, an objective measure determined by four factors: projectile weight, propellant weight, muzzle velocity, and firearm weight.

When a 357 SIG 125 grain bullet is fired at 1,350 fps from a 2-pound pistol, it has about 9 ft-lbs of recoil. Most consider it to have stout, snappy recoil.

When a 357 Mag 125 grain bullet is fired at 1,450 fps from a 2-pound revolver, it has about 10 ft-lbs of recoil.

While the 357 Mag generates more recoil energy than the 357 SIG, it’s not significant enough for most shooters to tell the difference. This section is a tie.

Accuracy

It’s important to remember that accuracy is more often a function of the (A) shooting platform or (B) shooter than it is of the (C) cartridge. The ammo, bullet design, firearm pairing, environmental conditions, trajectory, recoil, and shooter all play significant roles in determining how much accuracy a cartridge can exhibit.

When fired from handguns, these .357 caliber cartridges are highly accurate within close ranges up to 50 yards. A skilled marksman may hit their target at 100 yards with either pistol. The 357 Mag can be even more accurate when it is fired out of a lever-action rifle, although that just reflects the chief advantage of a rifle. With a longer barrel comes a bullet with a higher muzzle velocity and greater gyroscopic stability.

This section is also a tie. Accuracy is ultimately determined by the shooter, firearm, and ammo pairing, and these cartridges are similar by design.

Stopping Power: 357 Magnum vs. 357 SIG

“Stopping power” is difficult to define. It means different things to different shooters, but we should all agree that shot placement is more important. A poorly placed shot with a very powerful cartridge is likely to have less “stopping power” than a well-placed shot with a weaker one.

For brevity’s sake, let’s suppose stopping power is determined by penetration depth, size of the hole created (aka wound column diameter), and kinetic energy transfer.

The 357 SIG was designed to achieve similar ballistics as the 357 Mag, terminal ballistics included. It is no coincidence that they boast equivalent stopping power when they are firing similar bullets.

However, the 357 Mag can fire heavier bullets. These tend to strike with greater kinetic energy, as well as penetrate more deeply – the reason why we declare the 357 Mag’s potential stopping power superior.

Hunting

Neither of these cartridges was originally intended for hunting. The 357 Mag was marketed toward law enforcement; the 357 SIG, for civilian self-defense.

The 357 Mag has proven itself effective for deer hunting out to 125 yards with a lever-action rifle. Some hunters love the challenge of handgun hunting. Alongside the 44 Mag, the 357 Mag is one of those hunters’ favorites.

The 357 SIG has been used to harvest deer within 50 yards by some handgun hunters, but it’s really only a novelty. The 357 Mag’s substantially greater popularity wins this section.

Self-Defense: 357 SIG vs. 357 Mag

Both cartridges are a solid choice for self-defense. However, the 357 SIG has a distinct advantage because it is designed for a semi-auto instead of a revolver. Its smaller pistol makes the 357 SIG easier to carry. Its higher ammo capacity gives the shooter more margin for error during a high-stress life-or-death scenario. Its detachable box magazine makes reloading the 357 SIG quicker and easier, too.

The 357 SIG wins this section. Revolvers are certainly practical for defense, although most folks do prefer semi-autos.

Cost & Availability

While there are die-hard 357 SIG fanatics, there just aren’t enough for companies to justify mass-producing firearms and ammunition. 357 SIG ammo is available, but expect to pay more per round than you would for 357 Mag ammo, regardless of whether you buy JHP or FMJ loads.

357 Mag ammo. It’s cheaper. It’s easier to find. It wins this section.

Reloadability

The initial investment in equipment and supplies deters most shooters from handloading. If you can be bothered to make that investment (and learn how to do it), then you will discover that handloading lets you fire altogether higher-quality ammunition – and save money while you’re at it.

The 357 Mag has been around for decades. Plenty of reloading information and supplies are available for it. While the 357 SIG hasn’t been around for as long, plenty of reloading supplies and information are available for it, too.

This section is a draw.

Ballistics

The team at Ammo.com has gathered the ballistic information you need to compare each cartridge quickly.

357 SIG Ballistics

Note: This information comes from the manufacturers. The actual ballistic data obtained with your firearm can vary considerably from the advertised ballistics. Also, ballistics can vary from lot to lot with the same brand and type load.

357 Mag Ballistics

Note: This information comes from the manufacturers. The actual ballistic data obtained with your firearm can vary considerably from the advertised ballistics. Also, ballistics can vary from lot to lot with the same brand and type load.

Take a deeper dive into 357 Mag ballistics.

357 SIG Brief History

The 357 SIG round was developed in 1994. Sig Sauer, in conjunction with Federal Premium, sought to replicate the terminal ballistics of the 357 Magnum in a more compact, semi-auto package.

Sig Sauer took a page from the Smith & Wesson playbook to accomplish this and experimented with the 10mm Auto cartridge. The final design used the 10mm Auto as the parent case necked down to accept 0.355” (9mm) diameter bullets.

The 357 SIG fires a 125 grain bullet at a muzzle velocity of 1,450 fps; the same as a 357 Mag bullet fired from a 4” barrel.

Although bottleneck cases are common among rifle cartridges, very few handgun rounds have them. The 357 SIG is one of the exceptions. Its tapered case promotes more reliable feeding. Its bottleneck also increases the case’s capacity, thus making space for the powder requisite for such commanding ballistic performance.

The 357 SIG saw mild success in law enforcement circles, and agencies that adopted the new Sig cartridge reported favorable terminal performance in officer-involved confrontations. Although the 357 SIG developed a small and steadfast core of followers, it never achieved the popularity of the 9mm Luger, 40 S&W, or 45 ACP.

357 Mag Brief History

Elmer Keith and Phillip Sharpe began collaborating to increase the power of the 38 Special sometime during the 1930s. They designed the round to fire a 0.357” diameter bullet at a muzzle velocity of 1,450 fps from a 4” inch barrel. They also lengthened the 38 Special case by about 0.15” to accommodate a larger powder charge (as well as prevent a 38 Special cylinder from closing in the event a shooter carelessly loaded 357 Mag ammo into it).

They submitted their work to Smith & Wesson in 1934. The 357 Magnum entered commercial production the following year.

The new cartridge was primarily marketed to law enforcement agencies (including the FBI), which needed a more powerful handgun round to combat bootleggers and the mafia.

Since its adoption, the 357 Mag 125 grain JHP round has been considered the gold standard for personal defense cartridges. Regardless of your feelings toward revolvers, the 357 Mag’s defensive capabilities should never be underestimated.

Parting Shots

Now that you’ve finished reading our 357 SIG vs. 357 Mag article, you know that the 357 SIG only won one section (self-defense). Three sections were a tie (recoil, accuracy, and reloadability). The 357 Mag won three sections (stopping power, hunting, and overall cost).

We can see why the 357 SIG didn’t take off. It offers little more than the 357 Mag or other self-defense cartridges to justify its purchase. However, if you’re only choosing between these two cartridges for self-defense, then the 357 SIG is better.

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