I had heard you cannot simply neck the .40 S&W to .357 Sig because it will be too short. I have thousands of .40 cases and was pretty much out of the .357 so I decided to experiment.
Lubing the .40 case with a bit of Imperial Sizing Wax, I ran a few .40 cases through the full length .357 die. The .40 cases started at .850 and ended up .860. Yup they grew 10 thousandths. The .357 Sig standard case length is .865. I'm still .005 short, right?
Even though the .357 is a bottleneck case, it was designed to headspace on the mouth. It CAN be loaded to headspace on the shoulder, if desired. I adjusted the die to set the shoulder to allow the case to headspace on the shoulder in my barrel.
I lose .005 in the neck so bullet hold will not be quite as good, but I plan on using these for a moderate load using a 125 gr RNFP hard cast bullet. I will crimp a bit more than normal to keep the bullet secure. Since I am not relying on the mouth for headspacing that will not be an issue.
I will load some up (as soon as I replenish my Wheel Weight stock) and let you know the results.