Reloading 357 SIG

You need sizing dies that that provide good neck tension. That is key. And set the shoulder to the proper length.

Longshot, 800x, AA9, are a few powders I can think of off the top of my head for 1350+ fps with a 125 gr. bullet.

It's good to check with a dummy round that you don't get bullet set back.

I don't use any crimp. Some do with minimal bell mouthing and light crimp. You definitely don't want to swag the bullet.

I load for a HK P2000 and a 226, both converted .40s.

I started with the Dillon carbide dies, which have worked extremely well and allow me to skip the size with a .40 die, then size with .357Sig trick. I also don't lube my brass, just clean and polish well. I've used 800X and Longshot, Longshot is my favorite.

Biggest thing I've found with loading 357SIG is choosing the right bullet, you'll want a flat point or hollow point design with generous bearing surface and a short nose to work with the short neck. For practice loads I've had good luck with Berry's 125 FP "thick" coated and these from Extreme Bullets:

https://www.xtremebullets.com/9mm-124-FP-p/xc9mm-124fp-b0500.htm

Chuck R. said:

I load for a HK P2000 and a 226, both converted .40s.

I started with the Dillon carbide dies, which have worked extremely well and allow me to skip the size with a .40 die, then size with .357Sig trick. I also don't lube my brass, just clean and polish well. I've used 800X and Longshot, Longshot is my favorite.

Biggest thing I've found with loading 357SIG is choosing the right bullet, you'll want a flat point or hollow point design with generous bearing surface and a short nose to work with the short neck. For practice loads I've had good luck with Berry's 125 FP "thick" coated and these from Extreme Bullets:

https://www.xtremebullets.com/9mm-124-FP-p/xc9mm-124fp-b0500.htm

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Correct, a generous bearing surface is important.

Chuck R. said:

Biggest thing I've found with loading 357SIG is choosing the right bullet, you'll want a flat point or hollow point design with generous bearing surface and a short nose to work with the short neck.

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This was the only problem I had with the sig.

The bullets I've used so far are Delta Precision 124 gr. JHP, RMR 124 gr. JHP MPR, and Montana Gold 125 gr. FMJ. I have some RMR 147 gr. loaded up, but haven't shot any yet.

vaalpens said:

Here are a couple of pictures I have uploaded:

Here is another picture to show how I verify that the ogive is outside the mouth of the case:

I have not really documented how I set up the 357sig Lee FCD, but I will see if I can put something together and share.

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In this post, member @vaalpens uploaded a picture demonstrating how to see if your bullet bearing surface protrudes out of the case mouth.

I’ve found I get better neck tension if I don’t flare and crimp. I chamfer the case mouth instead before seating. I’ve never had bullet setback.
AA#9 is a good powder overall but I did have to switch to Bullseye when I was loading my 90 gr varmint loads because I was getting incomplete ignition with AA#9. 115 gr and heavier bullets were no problem with AA#9.

My experience so far has been that using the full length of the resizing die (Lee) provides the best neck tension despite setting the shoulder just slightly shorter than would be ideal. That coupled with absolute minimal case mouth flare (if any), and followed with the Lee Factory Crimp Die just to get sure.

New brass seems to hold bullets better than dry tumbled once-fired brass. As range ammo isn't chambered multiple times, bullet setback isn't a major concern. If you want to load carry ammo (for whatever reason), new brass really does seem to give increased friction through the neck. In my experience.

Alex G said:

Thanks all!

^ I’ve got Redding FL sizing dies

^What about AA#7? A little faster than #9, and I have a bunch of it for 9mm +P loads.

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AA7 will work. Western Powders has some load data for #7. You should be able to get close to 1350 fps, if that is what your goal is.

@vaalpens
Has posted info on loading .357 Sig and the results of some loads he has tested here.

edit:

I'm giving serious thought to the .357 sig.
I'm curious whether anyone has tried a .357 dia lead SWC?

I don't want to hijack this thread - But it seems relevant to the OP anyhow

Power Pistol and BE-86 have worked well for me.

Alex G said:

Will check it out, thanks!!

Definitely not hijacking haha, I’d like to see some info there myself! What about Hi-Tek or powder coated projectiles? Can they hold up to the velocity?

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I've been thinking that with the .357 sig being a necked case, it headspaces off the shoulder as opposed to the case mouth, as in most other rimless cartridges.
So that opens doors for a few things that might not be tried with typical cartridges.
Also the smaller bullet dia helps it feed to reliably, from what I've gathered.
There was another thread where a guy posted some data using .357 dia jacketed bullets for his .357 sig and there were no issues.
I probably have 50 lb of .357 bullets that I bought for my revolver a few yrs ago, and it would be great to put them to use.
It seems like the most serious issue would be the nose of a SWC bullet meeting resistance of some type, in the process of feeding, and forcing the bullet back, to create a high pressure situation.
But that risk might be minimized by the larger dia opening at the feed ramp.
It would be interesting to hear from someone who's tried it.

If you are worried about bullet setback, you can use a slower powder like AA#9 that fills the case. The powder volume won't allow setback.

JayBeeKay said:

I've been thinking that with the .357 sig being a necked case, it headspaces off the shoulder as opposed to the case mouth, as in most other rimless cartridges.

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The 357 SIG, technically, headspaces off the case mouth. But you can load it to headspace off the shoulder.

JayBeeKay said:

It seems like the most serious issue would be the nose of a SWC bullet meeting resistance of some type, in the process of feeding, and forcing the bullet back, to create a high pressure situation.

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All flat nose bullets would face this same risk, not just SWC.

JayBeeKay said:

I'm giving serious thought to the .357 sig.
I'm curious whether anyone has tried a .357 dia lead SWC?

I don't want to hijack this thread - But it seems relevant to the OP anyhow

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I have thought about loading lead bullets. I've read some have had good results with Lee's 120 gr. truncated bullets. Whichever bullet, the bearing surface would have to match up with the neck, wouldn't want the lube groove in the neck area. Definitely would have the bell mouth a bit to not shave the lead or coating.

Bottom Gun said:

If you are worried about bullet setback, you can use a slower powder like AA#9 that fills the case. The powder volume won't allow setback.

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Or possibly 800X.

I had a bunch of VVN340 I got in a trade and it has worked well with the Hornady 115 HAP. Very accurate combo. Best wishes!

In my experience whether the .357 Sig spaces of the case mouth or the shoulder is a matter of which one hits first inside the chamber. I haven't found any issues in chambering or firing my own loads. In fact the only loads I had an issue with was a box of factory range grade ammo that had not had the flare removed. Some other those didn't chamber first time, but they all shot eventually.

kcofohio said:

Or possibly 800X.

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I panic purchased 4lb of 800x about a yr ago because it was the beginning of what appeared to be an ammo famine.
I just figured that I'd come up with ways to make it work.
I loaded some max loads for .357 mag that I was about to try but got rained out.
It seems pretty versatile
I think I will follow through with buying a .357 sig barrel for my Glock and if I like it, I'll get one for my 1911
I'm seeing positive posts on the .357 sig

I have found a cut a way style Sheridan gauge works great for setting up dies because you can see the shoulder set back. Removes all guess work. Best wishes!