Headspacing .357 SIG

[klcarroll]

I started handloading .357 SIG almost 12 years ago, ...and it quickly became apparent that one of the first things the prospective reloader has to decide with this caliber is how to headspace it.

Like many, I gravitated towards using the case shoulder to control the headspace: I started that way, mainly because my Wilson Case Gauge was configured to measure relative to the shoulder. This worked well for me from a consistency standpoint, ...and using the shoulder for headspacing allowed me to form cheap, "plinking rounds" by reforming .40S&W brass. These "cheapies" functioned well, and even with the reduced loading I used in them, they were still more potent than typical 9mm loadings. (....And with the shoulder headspacing, the fact that they were .008" too short really didn't matter.)

Soon, however, questions began to arise: Every time I would drop a Factory Loaded .357 SIG round into my Wilson Gauge, the round would drop into the gauge a full .025" deeper than the Max Headspace shoulder on the gauge! I have tried Winchester, Fiocchi, Hornady, and DRT, and the result is the same!

The major ammo manufacturers are clearly producing these rounds to headspace on the case mouth, not on the shoulder. There is only one logical reason I can think of for doing this: ...Forming the case to headspace on the case mouth allows for a potentially longer neck to be created by setting the shoulder back a bit. In a short-necked case like the .357 SIG, every little extra bit of neck helps in the fight to properly retain the projectile, and fight bullet setback.

The obvious downside to headspacing on the case mouth is that the shoulder area will be much more severely worked, and case life will suffer: ......But in spite of that, I'm thinking that I will alter my setup to headspace on the case mouth so that I can find just a little bit more case neck.

What are your thoughts??

[ReloaderFred]

I've been loading 357 Sig since shortly after it came out, and I quickly learned that there are two datum points as far as headspace is concerned. The first is the shoulder, and the second is the case mouth. If either one of them, or both, are set too long, the rounds won't chamber.

Setting the shoulder back too far not only shortens case life, though I do have plenty of this brass, but it slightly reduces powder capacity. I run Accurate #9 in my 357 Sig loads, and it nearly fills the case, but not quite. Compressing the powder charge helps to prevent bullet setback, so I'm cognizant of the powder level in the case neck.

I just set up my dies so the loaded rounds will chamber in both of my 357 Sig pistols, which fortunately have very similar headspace.

Hope this helps.

Fred

[Ia.redneck]

I've been reloading the 357 Sig for awhile now too. I headspace it on the shoulder too. I do it so I can give the mouth a light roll crimp on my cast boolit to prevent it getting pushed deeper in the case. Too much neck tension will make the lead boolit smaller.

[cupajoe]

I really don't think the tiny amount of neck length increase would affect neck tension much at all but hey, if you think it will, go for it. You could make a few pieces of 357 Sig brass from 10mm brass, set to headspace on both the shoulder and case mouth and try it to see if it helps.

[dkf]

I have saw it mentioned already that it headspace on the shoulder but SAAMI says the case mouth.(looking at the drawing) I figure the case mouth is likely correct because of all the different factory ammo I gauged that has the shoulder bumped way back. I usually just kiss the sizing die to the shellholder and call it good as it chambers in all my guns that way and doesn't bump the shoulder back excessively.