Please note that this article looks at research and testing done by a variety of sources. Extreme caution should be taken when creating loads that go against accepted load data. This article looks at theory and our experience, and should not be considered recommendations about primers for the 357 Sig. When developing a new load for your 357 Sig, or any caliber, you should start with smaller amounts of powder and pressure and work up gradually.
About the 357 Sig Cartridge
The 357 SIG is a round that was created by SIG SAUER, along with Federal Premium Ammunition and Speer in 1994. The idea behind the cartridge was to offer a .357 caliber bullet out of a semi-automatic handgun. This meant that officers could have the stopping power of a .357 Magnum, but with greater magazine capacity, faster reloads and increased practical accuracy. The result was a big success and today there are many guns chambered for the round.
The 357 SIG is not actually a magnum round, despite what the name suggests. It’s actually pretty similar to the 40 S&W. In fact, most pistols chambered in 40 S&W can be converted to 357 SIG with just a barrel swap. That’s because the two cartridges share the same rim dimensions as well as overall length, and 40 S&W Primers are not magnum primers either, generally speaking.
What size primer does the 357 Sig take?
The 357 Sig cartridge takes a small pistol primer. We like to verify primer information and all other reloading data from multiple sources, so we recommend that you do this as well. We like to confirm with multiple published sources. We use reloading manuals from Hornady, Lee, Berger, and others.
Hornady Handbook of Cartridge Reloading
Can you use small pistol magnum primers in 357 Sig reloads?
Yes, you can usually get away with using small pistol magnum primers.
Primers have a metal outside, called a cup, and the small explosive charge used to ignite the powder in a cartridge. The bigger the primer, the thicker the cup, and the more or different explosive material is in the primer. If you’re watching pressure, you can usually load a thicker primer, as long as your hammer and firing pin has the strength to ignite the primer. Most pistols do have the strength to ignite primers much stronger than just a small pistol primer.
I asked my personal gun smith, who also taught me to reload his opinion on small pistol vs small pistol magnum and this is what he said about it: “I’ve tried both. Small mag is if you want fast loads. You need to burn a lot of powder quickly. You can over pressure the case quick so be careful. In the end if you are following good reloading procedures, load light and build up to what you want with either one.”
Why use other sizes of primers other than what’s in load data?
Obviously, we recommend that you try to stick with accepted load data, however, not every gun is the same, and sometimes a gun responds better to one powder or primer better than another. In addition to that, there have been primer shortages, and ammo shortages. Sometimes you have to do what you have to do in order to just get by.
Can I use small rifle primers in 357 Sig reloads?
Yes, usually you can use small rifle primers in most small pistol applications. They fit in the same size primer pocket, and we have found that most weapons have the power and ability to ignite these harder primers. Again, be sure to lighten your load to see how pressure will be affected by these stronger and hotter primers.
Can I use #41 small rifle primers in 357 Sig reloads?
Maybe, but again, this is where things get tricky. The #41’s have a harder cup and are very popular for reloaders who shoot primarily out of an AR15 platform. The AR has a free float firing pin, and because of that, the pin strikes the cartridge lightly when reloading. It’s designed to not be ignited on these light strikes. If your firing pin and hammer can hit really hard, then you should be able to use these. Reduce your load, and try it with proper safety measures if you need to.
Berger Bullets Reloading Manual
Can I use small pistol magnum primers in 357 Sig?
We’ve also gotten reports that yes, you can also use small pistol magnum primers to develop your loads. We also read a report that said for one manufacturer, they’re identical to the regular small rifle primers. Specifically, the CCI 550 Small Pistol Magnum primers and the CCI 400 Small Rifle Primers are the same size, with the same cup thickness. They’re also made from the same material and use the same explosive.
As always, do your own testing to confirm using safe load development practices.
What Primers Do I Use?
I initially developed my 357 Sig loads using regular small pistol primers. I tend to use either Federal or CCI primers.
Other Frequently Asked Primer Questions:
Can you use CCI 450 Primers or other small rifle magnum primers for 357 Sig reloads?
Again, maybe. Some guns may be capable of this and others may not. It is more determined by the gun rather than the caliber. Of course, these primers are hotter, so load lighter and do your own testing.
Where can I find 357 Sig primers for sale?
I buy from Sportsman’s warehouse and several local shops by where I live.
CCI primers for 357 Sig
CCI 500 primers are the commonly used cci primers. Look at your specific load data and see what it specifies.
CCI 550 Primers for 357 Sig
CCI 550 primers are a small pistol magnum primer. Most reloading data says to use regular small pistol primers, but many reloaders use the CCI 550s and do just fine. Be sure to do your own testing, and re-work up loads when you switch out a component.
What Winchester Primers should I use for 357 Sig?
We recommend the WSP primer, or small pistol primers.
Can you use CCI BR5 primers for 357 Sig?
Yes. BR 5 primers are good to go. They’re a match grade primer, so they’re a more expensive option, especially if you’re just planning on using them for plinking, but they work. In fact, some prefer them for precision loads.
What Federal primers can I use for 357 Sig?
- Federal 100
- Try other types of primers at your own risk, and please use safe reloading practices.
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