I use, and have ALWAYS used Blue Dot for my 357 Sigs. The 357 Sig is my carry gun these days. Amazing firepower.
Blue dot fills the care fairly well.
Here's my process:
1) Full length sizing with a .40 S&W full length sizing die. This touches ONLY the outside diameter. Carbide die makes it go fast.
2) Full length sizing with a 357 Sig full length die. because I have done most of the sizing work with the .40 die, there's no need to lube the cases. The shoulder and neck get properly sized, formed, and set easily.
3) Install primer (I run these on a Dillon 550b) in station 1
4) Almost zero bell mouth in that station, where the powder drops. You have to have some bell mouth to align the bullets, and I hand guide those in the next step.
5) Hand guide bullets into place, and set with an extremely light crimp from the bullet seating die. Not even a real crimp, just starting the process of pushing the neck back to where it will end up.
6) Lee factory Crimp Die to give a collet style crimp. This is the magic for avoiding bullet set back with this chambering.
When firing the Blue Dot loads at night, it's an amazing FIREBALL! Bad guys and Zombies will be blinded!