357 Sig


I’ve been looking around recently at some of the calibers that are making a comeback these days. Starting with the 10 mm that we all seem to love and even 357 sig. I was wondering everyone’s opinion on the round and some information on it to drop in this thread. I was looking at a chance to acquire a glock 31 in the near future. The other option is to go with a cheaper platform and do a barrel conversion for it. The cartridge itself is a great performer with it being necked down to 9 mm bullet on a 40 S&W casing. It easily outperformed any 9 mm Plus ammunition on the market by a factor of 250 feet per second. Some of the Underwood loads that I’ve seen online have posted in the mid 502 -600 lb of on Target.

So whats your thoughts on it?


If you are willing to stack it deep the .357 Sig is a fantastic round. I had one for awhile and have zero complaints outside of ammo availability. Its a super flat shooting high pressure round that does a decent job punching through stuff. I think its a .40 necked down to 9mm, @switchpod would probably know more about that though.


I saw that switchpod is doing a 10mm case necked down to a 9mm. I’m looking at doing it on a 8 inch barrel in the future for one of my “projects”. Zeke Shoots got me starting into the whole process of building and making your own so its has become addictive with all the reseach that comes with it.


Awesome question. Long ago I went with 357 Sig. my reason was ammo cost, but having said that you can also go with a necked down 10mm called a 9x25 Dillon. @MatteoThirteenSeventyOne let me know that they make all the dies for this round. About a month ago I was going to start making a chamber reamer and Matteo let me know I was already reinventing the wheel.
A other round you should look into is the 460 Roland. You can just but a barrel and recoil spring for a firearm that was chambered for .45acp. Look up the rounds and see if they fit your needs.

I went with .357sig, but I’m also a capacity baby. I don’t like trading power for less rounds.

Definitely talk with @MatteoThirteenSeventyOne he has been there and done that. He has even switched to steel cases so he can squeeze a little more power out of his cartridges with out having a case separation.


Don’t worry about the 460 Rowland, I am already tracking that. I was looking at a project for a conversion of my xD 45 tactical. It’s been sitting in my little safe for a long time. I saw the company that makes it and they offer a barrel and spring kit at a modest price but fair enough to say the least. I have to agree with you on the capacity issue. Even with my XD and the AGP mag extensions it comes out to about 16 rounds of 45 which would translate into 16 rounds of 460 Rowland with a 6-inch barrel.

I’m looking at the three five seven for its availability on the shelves and being a little more popular than the 9 by 25 Dillon i’m also looking at firing it out of 8 inch barrel. Also when it comes to yours do you I have a Glock 31 or a variant of a pistol in that size and frame? Everyone seems to do the compact or subcompact but I’m looking for a full size frame.

I didn’t know switching to Steelcase will give you that extra feet per second. I think you have to make a video on reloading steel case ammunition and how to do it for that caliber i’ve heard a lot of good things about it and I see that it was resigned to competition pistols only for some reason


You could also do a Polymer80 build and make it the caliber of your choice. The long-standing version has the capability to make a G31. They have just started the PF45 which will handle the 45ACP, 10mm and the 460 Rowland. @Greenwell_Armory was offering a preorder discount on them. I’m not sure now that they have been released.


Send me a DM you never know :wink:


No, but I wouldn’t mind having one. The 357 Sig pistol I own is a Sig 229, so yes it’s one of the shorter barrel applications.

When I went to the 10mm chambering I went for a little more flare with a Glock 40 MOS.

You are correct, but the switch allows you to load hotter with out as much of a fear of case separation.(some steel case will have less available area inside the case, and a normal load can become hot) I personally don’t reload steel case, but if I did it would be only for boxer primed cases, and using Full length sizing die with a lot of lube.
There are a lot of people that will give you a hard time about using steel case ammunition. Also when loading hot ammo (that I’m not recommending you do) you start off slowly adding more powder slowly, after shooting inspect your spent primer. If the primer is starting to flatten out stop and back off your loads. It’s all fun and games until you primer has a blow out and it becomes a mini torch cutting your firing pin and/or slide. Both things I think we can all agree we don’t want to have happen to our firearms.


I picked up a used LE Glock 22 Gen 3 (.40 cal) for a good price. I’m converting it to .357 Sig for which you only need a barrel replacement (in .357 Sig obviously) and replacement mags. Although I decided to make a project of it and am installing all new standard parts plus some upgraded parts including an extended mag release, reworking of the trigger springs, a trigger job (polish here, polish there), and a handful of others (can’t recall at the moment). Finishing off with the ever popular silver slide black frame Cerakote job.
I already have a nice Sub compact xDM in .40 cal and wanted to change things up with what looks like a very capable cartridge in the .357 Sig which may be more fun to shoot as well. If so I’m already to mass produce my own ammo on the Dillon 550. I’ll let y’all know how it goes…



I have enjoyed experience with a 23 glock swapping only the barrel, mags are same. 357 sig is a dandy of a round.


I corrected my post to reflect that I have a model 22 - not model 23 as I first stated. Which is where the mag replacement comes in.

Thanks for the info on your conversion, couldn’t get any simpler and you are happy with the results, I call that raging success. :+1:



[a bit off topic, but here it goes]

Speaking of Glock .357 Sig magazines… advertised capacity: 15 rounds. So just for the sake of experimentation, I replaced the stock floor plate with an alleged extended (+3) mag base. I could just manage to cram 15 rounds in it without the use of a loading tool, just bare fingers and thumbs. I didn’t attempt to load the mag with the stock floor plate while still installed (which I should have), but I’m chomping at the bit to get started with the rebuild and jumped the gun (ha, ha) a bit.

Anyone out there in Forumland have experience with these mags and/or extension bases? Do you have to use a loading tool to squeeze the last few rounds in?

I’m guessing that 15 rounds wouldn’t fit in the mag with the stock floorplate, but I’ve been wrong before.