Grrrrrr. . . 357 SIG Headspacing


August 25, 2010, 07:28 PM
Grrrr. . . can someone please, please settle this once and for all!

Headspacing the 357 SIG is controlled at the . . .

1) Case mouth

2) Shoulder

3) Extractor as below at 30:00

WTH! Extractor? :what:

Just started reloading about nine months or so ago and have reloaded .223/5.56, .270 Win., 9mm Luger, .40 S&W and now 357 SIG.
I do Google searches and still find some that say either "Case Mouth" or "Shoulder." Now with the ProArm broadcast we have the extractor and
as it turns out according to Google a few others out there saying the semiauto's headspace off the extractor! :scrutiny:
I have so far successfully loaded approx. 100 rounds of 357 SIG with Win brass, Wolf SP, AA #9 and MG 125gr FP 357 SIG bullets, got around 1275 FPS.

I'm using Dillon XL650, and for 357 SIG I use Dillon Carbide Dies, and a Lee FCD.

I have AA #9, HS6, PowerPistol, Bullseye, Bluedot and Clays powder.

Bullets are Montana Gold 125 gr. FP 357 SIG., Speer GDHP 9mm in 115 and 124gr and a few Hornady 9mm XTP in 147gr.

A variety of primers and brass.

Thank you for your time and consideration into this matter!

Wild(frustrated)Kow :banghead:

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August 25, 2010, 09:01 PM
Size it to headspace off the shoulder. We have plenty of .357 Sig reloaders here can can help.

August 25, 2010, 09:16 PM
I've been loading the 357 SIG for about a year now ... I found mine to headspace off the shoulder. I even played with some light loaded 40 S&W cases necked down which shot just as well as the regular 357 SIG brass, they were quite a bit shorter than the SIG brass. I mashed them with the hammer when I finished "playing" with them so as to not mix them up with my good brass.

My method for checking is to use my barrel as a gauge... because my reloads have to fit my barrel. Take the barrel out of the gun and drop the sized case in to see if it fits like it should. You can also mark the case with a marker or smut it with a candle to see where it touches the chamber. Do the same with a loaded round to see how it fits.

Are you having problems getting your headspace correct?

Jimmy K

August 25, 2010, 09:35 PM
I've been loading 357 Sig for about as long as it's been available and have about 12,000 rounds loaded so far in this caliber. Officially, this round headspaces on the case mouth, but practically, there are two datum points, the case mouth and the shoulder, both of which have a direct bearing on whether or not the round will chamber.

Anyone who loads ammunition for semi-auto pistols to headspace off the extractor is courting trouble. I've performed several experiments along this line and some pistols will shoot off the extractor and some won't. In any case, it's not a good idea and I don't recommend it.

The best course of action is to size the cases so there is approximately .003" of clearance at the shoulder. Any more, and you'll get case head separation at some point. Any less, and the rounds may not fully chamber, which could cause an "out of battery" condition, which in turn causes parts to fly off the firearm and normally some blood flow that can be quite distracting........... If the case is too long, they also won't chamber fully, and in some cases, the shoulder will collapse when the crimp is applied.

Hope this helps.


August 29, 2010, 12:38 AM
Info always helps and sorry I didn't back sooner on this thread.

Ok so it seems that the 357 SIG headspaces off the shoulder or the shoulder and the case mouth. Seems shoulder and case mouth would be best as reloaderfred points out you have two datum points, more is better right?

So if'n you all don't mind have a look at these reloads . . .

Tale of the tape, out of the five I randomly picked from my reloads each case measures almost exactly .860 and the one in the photo measured .8595. OAL was 1.133. I'm loading this on a XL650 with Dillion 357 SIG carbide dies. Obviously this cartridge is out of spec according to the Wilson Headspace Gauge. The case mouth protruds to far past the lip and the case seats to far into the case gauge. I have the die set down to the shellplate with a 1/4 to 1/2 turn more to slightly over cam. I do this with all my 9mm and .40 S&W. Obviously these are not the same type cartridge as the SIG is a bottle neck. These reloads have fired just fine, 12.7gr AA #9 at about 1278 FPS in a Glock 35, with KKM Barrel.

My analysis is that the shoulder is set back to far and the cartridge headspaced off the case mouth only. If it had not headspaced of the case mouth it may not have fired since the firing pin may not have struck the primer with sufficient force. If the cartridge is headspacing off the case mouth only, which means the shoulder is at least the same distance off the chamber shoulder as it is too low in the guage (?) is this situation dangerous (overpressure) or just harder on the brass, i.e. case mouth separation, in the long run? Is the solution to this problem simply to back off the die from the shellplate a 1/4 - 1/2 turn or so?

Thank you for your time and consideration in this matter.

August 29, 2010, 10:00 AM
Is the solution to this problem simply to back off the die from the shellplate a 1/4 - 1/2 turn or so?
Yes. Exactly.

Just because it fit and fired does not mean that the headspace, as measured using the shoulder, was not excessive. The Wilson gauge sure says it is. It will give you poorer case life than if you lesson that headspace.

I do not load .357 Sig, but I do load .400 Corbon, and the idea is the same for both. Size to minimum headspace off the shoulder for your barrel. It will lesson the chance of the brass letting loose on you in a high pressure round.

August 29, 2010, 11:53 AM
As Walkalong pointed out, and you've surmised, the shoulder is being set back too far, so you need to back off the die the proper amount to just give you enough clearance for the round to chamber. If you fire those rounds as they are a few times, the cases will stretch and the case head will separate, leaving the majority of the case inside the chamber. I ran into this problem with the 9x25 Dillon (the 10mm case necked down to 9mm), when a gunsmith chambered a barrel too deep for me.

Hope this helps.


August 29, 2010, 12:08 PM
Have you tried them by setting them in your barrel with the barrel off the gun?

Just as Fred said, your chamber could be different than the gauge you have, his was. I know that the gauge is the "standard" by which to measure, but what IF your chamber is deeper or shallower than the gauge?

That is why I use my barrel as "the gauge", because your ammo should fit your chamber not your gauge. Now if you have two guns or for some other reason then the gauge is the standard.

I had rather my ammo fit my gun... than my gauge.

Jimmy K

August 29, 2010, 06:06 PM
This forum is just awesome! Today you all have finally driven something into this thick skull, i.e. I learnt something! :D

I used the barrel chamber as a guide before I had my Wilson Headspace Gauge and it seemed to gauge correctly that's why I went ahead and fired those out-of-spec reloaded rounds. But since the 357 SIG also headspaces off the case mouth how would I know if the shoulder was correctly sized to within .003 of the chamber as reloaderfred suggests? What I should have done was JimKirk's suggestion to smut :p the cartridge with candle smoke to see where and if it touches in the chamber.
Doing this in conjunction with the headspace gauge gets you a custom fit of your reloaded cartridge to your barrel. Even though this process is a bit more complicated in the initial phases over reloading a straight wall case the fact that it involves smutting :rolleyes: makes it all worth while eh? :D

Would it be worthwhile to outline these steps or am I the only knucklehead that has missed these finer points?

August 29, 2010, 06:32 PM
You're not a knucklehead. You just had a few questions and we had a few answers, simple as that.

There are several older threads on this very subject and caliber, so there's really no need to detail it all again. All it really boils down to is using the same methodology for loading 357 Sig as for bottleneck rifle rounds.

You can also use a Sharpie on the case, or Die-Kem. Either one will work and it's not as messy as the candle method.

As for case gauges, a lot of people who were cruising along just fine have been messed up by purchasing a case gauge. I have and use them, but I realized right away that they're not chambers, just guides, and my chambers are what I'm loading for. Once you buy into that philosophy, life will be simpler.

Hope this helps.


PS: I'll bet it's really hot in Clovis right now. It's 65 degrees here on the coast at 3:30 PM... (just had to rub that in, since I retired from just south of you)

August 29, 2010, 06:59 PM
Happy to hear you're out from behind enemy lines. The temp is down quite a bit from it's high this last Wednesday of 111F, :fire: today it was barely in the 80's and is now mid-70's. I'm lousy at searching but I'm on the hunt for those threads you mentioned. Haven't shot it much but I think I really like this round and not just for the smut. :p

Thanks for all the help.

August 29, 2010, 08:40 PM
Glad it has worked out !!!

Yes it is a short bottle neck just like a small rifle case...

Yes the candle is messy, but it works!! I can't ever find my markers when I need them.

Now go shoot a bunch !!

Jimmy K

August 29, 2010, 09:45 PM
Here is one old thread:

I'll find you another one in a minute.


August 29, 2010, 09:48 PM
And here is another old thread:

These should help you out some. Glad it's cooled off down there. I don't miss it.


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