6 replies to this topic

[ehd]

As I am waiting for my dies to get here I have been reading numerous articles on reloading the 357 sig. The speer manual says that the headspace is off the case mouth ,such as the 9 mm or 40 s and w Not off the shoulder of the bottleneck. I decided to find out what was truth as Tawnoper touched on this a few days ago.. I took the barrel out of my glock and measured an empty fire formed case protrusion out of the barrel. then done the same with a loaded factory ammo. the factory sat about .020 further in the barrel. Next I measured the distance to the machined surface that the case face would space off of. .060 from the end of the factory case , both fire formed and unfired brass. Way too far to be used as a headspace margin. I put some die on the case to see where it shouldered and it was at the base of the tapered neck just like a rifle. the latest Speer edition is WRONG! Now checking with some factory ammunition that I had on hand it seems that the base of case to shoulder length(which is critical for headspace) is all over the place for length. Some are as little as .010 .some as far as .040. The question I have is how much headspace do you give ,(bump the shoulder back) from your fire formed case from that gun? I have shot all these rounds in the glock 31 with no issues, but .040 headspace should be considered unsafe. I also checked primer contact with those cases, and they were struck visibly lighter ,but still went off. Tawnoper you were correct about the shoulder, and thank you for your input.

[Bisley]

.357 SIG maximum C.I.P. cartridge dimensions.[1] All sizes in millimeters (mm).Americans would define the shoulder angle at alpha/2=18 degrees. The common rifling twist rate for this cartridge is 406 mm (1 in 16 in), 6 grooves, Ø lands=8.71 mm, Ø grooves=9.02 mm, land width=2.69 mm and the primer type is small pistol.Several sources have published contradicting information regarding .357 SIG headspacing.[3] According to the official C.I.P. (Commission Internationale Permanente Pour L'Epreuve Des Armes A Feu Portatives) 2007 guidelines the .357 SIG headspaces on the shoulder (P2-H1). Some US sources concur this C.I.P. ruling.[4] US reloading supplier Lyman once published the .357 SIG headspaces on the case mouth (H2).According to the official C.I.P. (Commission Internationale Permanente Pour L'Epreuve Des Armes A Feu Portatives) guidelines the .357 SIG case can handle up to 305 MPa (44,236 psi) piezo pressure. In C.I.P. regulated countries every pistol cartridge combo has to be proofed at 130% of this maximum C.I.P. pressure to certify for sale to consumers.The SAAMI pressure limit for the .357 SIG is set at 275.80 MPa (40,000 psi), piezo pressure.[5]And I wouldn't fret too much, the dies should have detailed instructions with them. Go by what they say, and you should be just fine.

[ehd]

thanks Bisley for the info.

[tawnoper]

The question I have is how much headspace do you give ,(bump the shoulder back) from your fire formed case from that gun?

As we spoke about earlier ehd...I'd bump back "all" bottleneck fire formed cases about .002". That is where one of those gauges are worth their weight in gold. Remember though...those cases are now ready to be fired off in your gun only and may not fit someone elses. Another thing that some people do when reloading for auto pistols is not loading the bullet deep enough. It will cause head space problems too and will usually not let the pistol go to battery.

[ehd]

As we spoke about earlier ehd...I'd bump back "all" bottleneck fire formed cases about .002". That is where one of those gauges are worth their weight in gold. Remember though...those cases are now ready to be fired off in your gun only and may not fit someone elses. Another thing that some people do when reloading for auto pistols is not loading the bullet deep enough. It will cause head space problems too and will usually not let the pistol go to battery.

Thanks for the info. the gauge and the dies should be getting here soon. What i found interesting is some factory ammo loaded by a small custom Mfg. co. had the shoulder pushed back .030. there case length was right on, as well as there overall length.

[tawnoper]

.030" is substantial. I would be very suspicious if that was the case. The way you are measuring is tough to get an accurate reading. .010" is alot. In all honesty reducing the shoulder back 1/32" would probably collapse the case or really deform it.Most all ammo mfg will size their rounds right at the bottom of tolerance so they will chamber in most anything. They want some slop.On the .357 Sig you have kind of a dilemma that straight walled cases do not have. I'm sure it was designed to headspace off the mouth like it's parent 40S&W...and will do so provided the shoulder is setback far enough to allow. Once it is fired it conforms to your chamber from the base to the shoulder (same on all rifle cases) Once you take a once fired case and resize or squeeze it back down in your die it will usually cause the shoulder to push forward slightly. This can create a condition that will not allow your gun to go to battery. You want to size the case down just enough that it bumps back the shoulder a couple thousands...on all bottle cases.Check out this guys link to his nice little headspace tool...it explains it pretty well.Headspace tool

[ShooterJohn]

Hey I have the Belted Magnum Collet Resizing Die for a couple of cartridges I shoot and the magnetic scope level from Innovative Technologies. They are really well made nice tools. I'll have to get that Digital Headspace Gauge now. Thanks Ed.