Wait a second, isn’t the Glock 20 chambered in 10mm Auto? What does .357 SIG have to do with the Glock 20 then? I’m glad you asked! The Glock 20 is awesome, but you can have even more fun with the “G20” with the addition of inexpensive drop-in barrels for different cartridges. With my Glock 20, I can shoot 10mm Auto, 40 S&W, and .357 SIG by swapping out just the barrel, no other parts or modifications are needed! What’s more, these barrels only cost about $100. (for the Lone Wolf variety I’m using) so it doesn’t take a bunch of cash to “expand your Glock 20’s horizons”. I already wrote about my experiences with the Lone Wolf 40 S&W drop in barrel, now it’s time to put the .357 SIG barrel to use!
My journey towards reloading and shooting .357 SIG has been a familiar one: excitement, preparation, then waiting for some time to explore this new cartridge. While this project was sitting on the back burner, I saw an email in a discussion group: 2000 pieces .357 SIG once-fired brass: cleaned, and with the same headstamp. This was just what I was looking for, and was the needed “bump” to get this project going. Soon I would be shooting .357 SIG for the first time: with my own handloads.
Above you see my Glock 20SF with 10mm Auto factory barrel, the Lone Wolf 20357N .357 SIG conversion barrel (foreground, left), and the Lone Wolf 2040N 40 S&W conversion barrel (foreground, right). A shooting package that fits in the stock Glock 20 case, but shoots three different cartridges. This is an awesome setup!
About .357 SIG
The .357 Sig cartridge was designed and developed by SIG SAUER with the motivation to replicate 357 Magnum ballistics in a more compact cartridge that would be easily adapted to semi-automatic handguns. Starting with the 40 S&W cartridge* (more or less- see note below), the case mouth is necked down from the typical 40 caliber dimension (0.400″) to accept 9mm bullets (0.355″). The overall approach was similar to many “wildcat” rifle cartridges: neck down the case to accept a smaller diameter bullet that will fly faster than the bullets from the parent cartridge from which it was adapted. Sounds interesting doesn’t it? I guess I naturally gravitate to “the unusual”, so as you can imagine, I’m excited to shoot and reload .357 SIG: it’s definitely something different! I’m also curious to try the .400 Corbon which is essentially a 45 ACP (which takes a 0.451″ bullet) necked down to accept 40 caliber (0.400″) bullets. .357 SIG never took off quite how SIG had hoped it would, but it does retain somewhat of a “cult following”.
*Note here that you can’t form .357 SIG from 40 S&W brass, because you’ll literally “come up short”- the 40 S&W case is not long enough to be formed into a .357 SIG case. Now, I know you may be thinking “what about 10mm Auto cases”? From what I understand, .357 was *not* designed/developed to use large pistol primers, so 10mm formed cases don’t work either. What does this mean? If you want to reload .357 SIG, you should find range pickup brass or new factory brass.
Above you see three 357 SIG cartridges loaded for this article, and my Glock 20 with Lone Wolf .357 SIG drop-in barrel installed. This .357 SIG drop-in barrel has a rather “substantial” muzzle profile as you can see in the picture.
Reloading the .357 SIG
Reloading for the .357 SIG is relatively straightforward, but there are some special considerations that warrant close attention. The “standard” loads for this cartridge include 124 grain and 147 grain 9mm bullets, and the .357 SIG will utilizes small pistol primers (not magnum).
Here’s a high-level summary of what’s used to reload .357 SIG:
- Cases: new or range pick-up (forming not advised per note above).
- Bullets: 9mm in 124 grain (best to duplicate 357 Magnum) or 147 grain. Hornady lists load data with bullets ranging from 90 grains to 147 grains.
- Primers: Small Pistol (standard, not magnum).
- Powder: Standard 124 grain load spans faster powders like Unique (on the faster side) to Blue Dot on the slower side (always consult a reloading manual to find an optimum powder).
There are two things that need special attention when loading the .357 SIG:
- Headspacing and shoulder setback: contrary to much mis-information on the internet, .357 SIG headspaces off the shoulder (consistent with bottleneck rifle cartridges), not the case mouth. This means you need to pay close attention to your seater die setup, use a quality case gage, and adjust the sizer die based on the desired shoulder setback (an important safety consideration, and an important criteria for reliable functioning of your loaded ammunition). Another important note about .357 SIG shoulder setback: factory .357 SIG brass (and ammunition) may have excessive shoulder setback to account for chamber variance which is another important reason to use a case gage. You will need to decide how much shoulder setback you want, but it’s important to stay within the minimum-step / maximum step range as indicated by your case gage.
- Bullet Crimp: One of the common complaints from people attempting to load .357 SIG is bullet neck tension and crimping issues. I read-up quite a bit on this issue, and decided to use a LEE .357 SIG pistol die set with a LEE .357 SIG Factory Crimp Die (purchased separately). The LEE Factory Crimp Die seems to work best for these kinds of bottleneck pistol cartridges (namely .357 SIG and .400 Corbon). I had no issues with bullet crimp or bullet neck tension, and had a 100% functioning rate, so I’m glad I went with these dies.
Here’s a picture of the loading setup using my Hornady Lock-N-Load AP 5-station progressive reloading press:
In the picture above, you see the following dies from left to right:
- Powder-through expander (works stand alone without charging, or can use for case-activated charging and expanding using a LEE powder measure like the LEE Auto Drum).
- Factory Crimp Die
Don’t forget to use your case gage when setting up the sizer die! Here I’m using an L.E. Wilson .357 SIG case gage.
The loading sessions (for 124 grain loads, and for 147 grain loads) went very smooth, and I was surprised at how well Hornady One-Shot lube worked (I don’t use for bottleneck rifle sizing). Here’s the load data for the ammunition loaded for this article:
- .357 SIG range pick-up brass (Speer headstamp)
- Hornady 147 grain 9mm bullets (Hornady #35580)
- Federal Small Pistol Primers (No. 100)
- Hodgdon CFE Pistol powder – 6.2 grains
- 1.140″ COL
Use load data at your own risk. Ultimate Reloader is not responsible for errors in load data on this website. Always cross-reference load data with manufacturer’s published data.
I have found the .357 SIG to be relatively straightforward to reload for. I did however do quite a bit of research for this project including talking with shooting industry experts in order to optimize my .357 SIG reloads and corresponding workflow. I think .357 SIG is a lot of fun, and love the fact that I can use my Glock 20 to shoot and develop loads for .357 SIG. I think .400 Corbon may be next!
Special thanks to Daniel Reichert, President of L.E. Wilson for his collaboration on this article, and technical insights related to the .357 SIG cartridge.
Do you have experiences to share related to reloading for .357 SIG? Please leave a comment!