9x25 dillon shoulder datum diameter?

[nhyrum]

So. I've been fighting some feeding issues. pistol is a rock island 10mm double stack with a custom reamed bar-sto barrel. every once in a while a round wont QUITE chamber, and usually a soft bump of my palm sorts out the issue. I believe its either the neck area bulging during seating, or an issue with the shoulder. I believe the neck is the issue, but I decided I'd measure from the case base to the shoulder, since its an easily measurable dimension. My chamber is a bit unique, and im trying to get the gun to run in uspsa open, and shes almost done! just this last small issue!

A bit of fore-word. cases were decapped using a universal decap die before first measurement. Dies are Dillon carbide dies, press is a Dillon 650. cases were measured and ran through the press individually, measured before and after each step, measured 3 times, making sure the calipers reset to zero, and making sure I got the same number three times. I used a forester datum dial kit, with the .400 hole. dies, toolhead, and the press is all secure. the calipers never touched the table, and were held securely in my off hand while using the press.

after looking at how wildly the shoulder is moving, and not going back anywhere near the same number. I'm coming to the conclusion that the .400 bore is just too large, since it sits at the very bottom edge of the shoulder. before I order a custom dial from forster, I just want to verify that I'm coming to a valid conclusion. I believe the diameter I need would be .380 looking at the chamber drawings?

since i cant get the image small enough, I'll link the google sheet.

https://docs.google.com/spreadsheets/d/1YONw4w140vEnJ1M-zXjY8VJ1KPP4P_6UOJtNr4ZJD3U/edit?usp=sharing