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The Ultimate Reloading Manual
Wolfe Publishing Group
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The Ultimate Reloading Manual
hodgdon load data

.357 Sig (using Hornady bullets)

Author: Brian Pearce / Wolfe Publishing Co.
Date: Jul 12 2013

The .357 Sig was a team development between SIG Arms and Federal Cartridge in 1994, and based on necking down the .40 Smith & Wesson case to accept .355-inch bullets. It was intended to easily outperform and give notably greater punch than the popular 9mm Luger, which it has clearly accomplished, while being chambered in pistols of similar size. While most bottleneck pistol cartridges have had limited acceptance, the .357 Sig has been well received, and its popularity seems to be steadily increasing.

Handloading the .357 Sig poses some challenges. Bullets should measure .355 inch; .357-inch bullets intended for the .38 Special and .357 Magnum revolver cartridges should never be used. The Hornady 9mm/.355-inch XTP-HP pistol bullets designed primarily for the 9mm Luger are suitable for handloading the .357 Sig; however, not all 9mm Luger bullets are suitable choices. For example, many 115- and 124-grain FMJ roundnose bullets that feature the long NATO style nose leave insufficient bearing surface for correct case neck tension when housed in the extremely short neck of the Sig (and seated to the correct overall cartridge length). As a result, bullets can be deep seated when hitting the feed ramp, which can result in dangerous pressure curves. Thus, the 115-grain Hornady FMJ roundnose is not recommended. The 115-grain XTP-HP, or roundnose bullets designed specifically for the Sig are recommended.

A two-die set of RCBS dies was used to develop the accompanying data. Cases should be full length sized to assure correct chambering. Problems arose when seating bullets, including tilting before they could be seated, damaging the case mouth. The die was adjusted every possible way, but the results were less than perfect. As a remedy, an expander die that would flare the case mouth just enough to let the bullet get a "start" was made, which resolved that problem. It is important to note that this "custom" die did not have an expander ball, but rather just slightly flared the case mouth to keep the bullet straight and just inside the case mouth to permit seating and prevent case buckling. In this fashion, case mouth and bullet fit remained tight.

In spite of the Sig being a bottleneck cartridge, it headspaces on the case mouth. As a result, cases should be within the minimum and maximum recommendations, and a taper crimp should be applied as a separate step after bullets are seated.

Winchester Small Pistol "standard" primers were used in the accompanying data. Most loads were cross-referenced in a Glock Model 31 and a Sig 229, as well as several factory loads. In many instances the primer firing pin indent was completely flattened on fired cases, which is normal. Industry maximum average pressure is 40,000 psi.