Loading the .357 SIG

Petty, Charles E


CAUTION: Technical data and information contained herein are intended to provide information based upon the limited expierence of individuals under specific conditions and circumstances. They do not detail the comprehensive training, procedures, techniques and safety precautions which are absolutely necessary to properly carry on similar activity. READ THE NOTICE AND DISCLAIMER ON THE CONTENTS PAGE OF THIS MAGAZINE. ALWAYS CONSULT COMPREHENSIVE REFERENCE MANUALS AND BULLETINS FOR DETAILS OF PROPER TRAINING REQUIREMENTS, PROCEDURES, TECHNIQUES AND SAFETY PRECAUTIONS BEFORE ATTEMPTING ANY SIMILAR ACTIVITIES.

THE .357 SIG came to us in 1994, and some are still trying to figure out what to do with it. In simplest terms, it is a slightly longer .40 S&W case necked down to hold a 0.355″-diameter bullet. The intent was to create an automatic pistol cartridge that duplicated the ballistics of the famed 125-gr, .357 Mag. revolver cartridge. Depending upon how you crunch the numbers. it does-or at least comes close.

Several prominent law enforcement agencies have adopted the cartridge, but it is generally viewed with only mild interest by the civilian market. In its 4th Edition Loading Manual Sierra writes,”Providing ballistics remarkably similar to the .38 Super, 9 mm Action Express and 9 mm Winchester Magnum (none ot’ which ever developed a following in law enforcement circles) it is difficult to predict what the future may hold for the .357 SIG.”

You cannot make .357 SIG brass by simply sizing .40 S&W cases. The resulting case will be too short and, since the cartridge headspaces on the case mouth, could lead to problems. Nor can you use 10 mm Auto cases for they have large pistol size primer pockets that could lead to serious problems with ejectors designed for cases with small primers, and the internal dimensions are different, too

Fans of the .357 SIG speak of its mild recoil and excellent reliability of function. One of the benefits of reducing bullet weight is less recoil. SIG’s oringinal offering was in its P229, but since then several others makers, including Glock and S&W, made pistols chmabered for it. And, in precedent-setting fashion, other ammunition makers, such as Honorady, Remington Speer and Cor-Bon, quickly followed Federal and began to offer the cartridge, but it is not exactly setting the world on fire in terms of popularity. In its defense, I must state that it is far more pleasant to shoot than loads with comparable velocity in a revolver. Such is the nature of the automatic pistol-that it absorbs some of the recoil via the mechanism.

Factory ammunition for the .357 SIG is mostly loaded with either 125- or 150gr. bullets, but technically any 0.355″diameter 9 mm bullet can be used. Factory ballistics are 1350 f.p.s. for the 125-gr. and 1150 f.p.s. for the 150-gr. loads when fired from a 4″ test barrel. Several factory loads were fired from a SIG P229 with a 3.8″ barrel and measured at 10 ft. using a Pact Professional chronograph.


Federal 125-gr. FMJ/1318

Federal 125-gr. JHP/1317

Speer 125-gr. Gold Dot/1362

Cor-Bon 125-gr. JHP/1313

One of the things you really have to watch out for is the very short (0.15″) neck. Successful loading of any cartridge requires that the bullet be held firmly in the case neck, but when you have such a small area to work with it takes careful attention to detail to provide adequate bullet pull. To do otherwise is to invite two very different kinds of trouble.

Foremost of these is that the bullet can be pushed back into the case during the feeding cycle and result in pressure increases that can be hazardous., The second, less serious, consequence is that inadequate bullet pull may contribute to erratic velocities due to incomplete powder burning. “The 0.355″diameter bullets with flat tips will be best in avoiding overall length problems,” said Speer Loading Manual Editor Alan Jones.

In many ways, loading the .357 SIG is more like loading rifle, rather than pistol, ammunition. But, unlike most bottleneck rifle cartridges that headspace at a point on the case shoulder, the .357 SIG headspaces on the case mouth. Case stretching does not appear to be excessive, or a problem, but it would be prudent to monitor case length and trim if the case exceeds the maximum 0.8650″ length. Since it is a bottleneck case, carbide dies are not a practical reality, so it’s a step backward for many handgun loaders who are used to that convenience.

Still, it’s easy enough to load as long as you follow a couple of rules. It is absolutely imperative that the brass be squeaky clean. 1 mean really clean. And this I know from sad personal experience. If the brass has even a tiny amount of grit the sizing die is going to be scored and often ruined. And so will the cases run through it.

The other inflexible rule is that cases must be thoroughly lubricated before sizing. Case lubrication is one of those things where you think, “if a little is good a lot will be better.” Sadly that isn’t true. The .357 SIG case is pretty thin and too much lube will cause dimples to be formed in the shoulder. My experience has been that the spray lubes like RCBS Case Slick or Dillon Spray are most convenient for this type of job, but they can be overdone.

Even though there are more than a few drawbacks to loading the .357 SIG, when those are recognized and avoided the cartridge is actually pretty easy to load. It shows a distinct preference for powders in the medium to slow range. One of the benefits of the bottleneck case is that powder capacity is increased a little and the .357 SIG will work well with powders that we might think would be too slow. The most current loading data is found in the Speer 13th Edition Lading Manual and is reprinted here with their permission. Speer’s data shows that Accurate No. 9-a powder I usually think of for the .44 Mag.-gives the highest velocity with its 125-gr. Gold Dot and the 147-gr. projectile responds best to Blue Dot, also a traditionally magnum powder.

One powder that seems to be especially happy in the .357 SIG is Alliant Power Pistol. While there are any number of powders that will safely duplicate factory loads. Power Pistol allows a bit more velocity with very satisfactory pressure levels.

During the course of trying a number of different loads, I worked up to the maximum loads for Power Pistol listed in Alliant’s latest Reloaders” Guide. It was the most remarkable incidence of my gun producing exactly what the manual said it would that I have seen in years. The loads listed are maximum, so we recommend that they be reduced by 10 percent to start. Alliant does not state which cases were used. but reports that it used Winchester primers. My loads were assembled in Federal brass with CCI primers and loaded to a length of 1.135″. This is especially remarkable because Alliant’s data probably developed in a 4″ barrel whereas my results come from a production SIG Arms P229 with a 3.8″ barrel.


Accurate Arms Co. (Dept. AR), 5891 Highway 230 West, McEwan, TN 37101; (931) 729-4207

Alliant Powder Co. (Dept. AR), P.O. Box 6, Radford. VA 24141; 1800) 276-9337

Hodgdon Powder Co. (Dept. AR), P.O. Box 2932, Shawnee Mission, KS 66201; (9131362-9455

Hornady Mfg. Co. (Dept. AR), P.O. Box 1848, Grand Island, NE 68803; (308) 382-5761

Sierra Bullets (Dept. AR), 1400 West Henry St. Sedalia, MO 65301; (660) 827-6300

Speer (Dept. AR), P.O. Box 856, Lewiston, ID 83501; (800) 627-3640

Vihtavuori Oy (Dept. AR), 124 Ellis St., Bensenville, IL 60106:(630) 350-1116

Copyright National Rifle Association of America Sep 1999

Provided by ProQuest Information and Learning Company. All rights Reserved

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