I don't have a Dillon press, so I also don't have the Dillon powder drop and expander system. 9X25 are my first set of Dillon Dies, and they have been a learning experience. I normally use Lee dies, and I guess I just understood all of their quirks and didn't think about them any more...The Dillon dies have their own quirks...
I purchased the Lee .357 Sig Dies so I would have a powder through expander and a (more appropriate for my press) Lee-style bullet seat/crimp die.
I find that the Dillon Sizer die extremely undersizes the neck, and my Lee .357 Sig powder-thru expander didn't have quite a long enough expander to open up all of the neck and allow bullets to seat properly. I kept getting crooked seating, collapsed necks and some wrinkled shoulders. I had to re-run the loaded cartridge through the sizer die to allow the round to chamber. I was getting pretty frustrated when > 50% of my cartridges wouldn't chamber properly!
I found that pre-forming the brass with a .357 Sig die set to the proper 9X25 shoulder REALLY helps! Now, I don't have nearly as many problems with crooked seating or collapsed shoulders! I run NEW 10mm brass through the .357 Sig die FIRST, then through the 9X25 die. Now, I don't see that little 'ring' around the neck that Dillon talks about in their Die Brochure.
I am beginning to think that the combined seat/crimp operation is not a good idea for a shouldered cartridge. I now get a few wrinkled necks with brass that is slightly long. I probably need to Seat the bullet with no crimp, then crimp separately (Which is what the Dillon dies already do... I just don't have enough stations on my Pro 1000! DOH!)
Hope this helps!
Are you doing Things Right?
Or doing the Right Things?