From the answers I received to an earlier question about necking down 40 S&W's to .357 Sig it sounded to me as if the Sig round headspaced on the shoulder. Am I correct in this or all wet?

Thanks

Dennis

yes, it headspaces on the shoulder.

Thanks for the reply, I thought that was the case but I haven't ever reloaded for mine and I just wanted to check before I ended up as a statistic .

With brass so plentiful WHY would you even fool with necking forties down?? Plus from what the SIG factory people have stated the .357 is NOT merely the .40 necked down. There are some differences in web thic
kness,etc. Plus I beleieve when you neck down forties you end up with an even shorter neck.

FN in MT

I'm not an expert by any means, but I believe 357 sig was designed to headspace on the case mouth, not the shoulder. One of the few bottleneck cases that don't headspace on the shoulder.

Andy

it headspaces on the shoulder according to SAMMI.
But there is some cofusing information out as can be see in the two conflicting articals below.

Wikepedia says that it headspaces on the case mouth, but has no mention of the SAMMI datum dimentions or where they are taken from on the case.
http://en.wikipedia.org/wiki/.357_SIG
WIKIPEDIA's information is incorrect.

This artical claims the headspace is off the shoulder, with proper referance to the SAMMI spec and the headspace datum dimention from he shoulder.

copied from, "real guns", Over thingking the 357 Sig...again Part I

Initially, gun magazines reported the SIG cartridge was designed to headspace on the shoulder, then at the case mouth and shoulder, then finally only at the case mouth. Personally, I think this progression of proper headspace description followed the brass shortage, with SIG not wanting to dampen the momentum of a new pistol launch with a shortage of ammo and temporarily will to ok almost anything that could fill one of their new guns. When correct brass became available, a new sense of technical integrity developed within SIG, and the press, as they began citing the SAAMI published spec, a spec that had been in place all along. Of course, concurrence of opinion is nowhere in sight.

If the 357 SIG case really headspaced on its mouth, use of a short formed 40 S&W case would indeed create a headspace problem, but it does not. Factory brass headspace dimension, case head to case mouth, typically run (picture left) .858", formed from 40 S&W brass .848" and Starline brass .858". The SAAMI case spec is 855"~.865", but the chamber headspace dimension spec is .865"~.877" which means, there would be virtually no time when any 357 brass would make contact at the case mouth. Simply stated, just about every time a 357 SIG cartridge is chambered in a SIG or similar pistol, it is headspacing on the cartridge shoulder and not the case mouth. I've loaded lots of ammo based on reformed .40 S&W before 357 SIG brass was generally available, and I occasionally do it today, mostly because I can.

As further reinforcement that the 357 SIG headspaces on the shoulder - 357 SIG "Go" - "No Go" gauges check at the shoulder datum line, not the case mouth, and reloading equipment manufacturers favor headspacing on the shoulder. Hornady, Lee and Redding dies roll crimp rather than taper crimp. Cases that headspace at the case mouth at not roll crimped, they are taper crimped. Redding does offer a taper crimp seating die as an option. RCBS's two die set forms a roll crimp. My set of RCBS dies included a slip sheet that specifically instructs how to produce 357 SIG cases from 40 S&W brass. In addition to the sizing instructions, the slip sheets go on to explain the under spec case length of the resulting formed case, offers a caution regarding potential problems, then puts the caution into context by indicating they never experienced a problem using cartridges made through this process.

This artical shows excelant images of the headspace gages and you will notice they have no provision for locating the case mouth.
http://www.realguns.com/Commentary/comar25.htm

Thanks Rusty, I stand corrected!

Thanks for the replies. I know that I can buy Sig brass all day long, my reason for asking was similar to Rusty's reason for using 40's, just to say that I can.

Thanks
Dennis

Just to set the record staight, I copied and gave credit for all that info. It's not "my" reason for using .40S&W brass, its the reason for the author of that artical.

Just don't want to take credit where it isn't due.