Sorry I was out of town for a few days...
I use the RCBS 9mm expander die to set the neck expansion/tension to very good tollerances it will also flair enough to allow cast bullets in the 9x25Dillon cases.
The Dillon Sizer/Case forming die can size the cases too much...by that I mean it will set the shoulder back too far if care is not taken to adjust the die precisely...yes it looks like the case mouth is flaired but it is actully undersized as you have found out. This is why I used my RCBS 9mm die set to do the case mouth work. This has provided very straight case neck, with great neck tension on the bullets to eliminate any set back potential, and aids in the bullet seating also.
I seat my bullets with the Dillon 9x25 seater die and crimp with the Dillon 9x25 taper crimp die...yes some seater plugs will leave a shinny "mark/ring" on the XTP bullets.
I wish you had the Chrony to check you velocity with those loads, please let us know how you make out!
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