What brand of dies are you using?
Just a guess would you be using a Lee Collet die and work harden brass that is leaving you with next to no neck tension.
Hopefully I’ll be bringing it home after work tomorrow. I still have extractor and rail work to finish on it yet.
Exciting times ahead.
Edit to add a shout out to 4D Reamer Rental for the reamer.
When I did my 375 Wby , my original plan was a 8mm RM. I just wanted the 375 more. If another magnum bolt Wby Vanguard falls in my lap there will be a Shilen 8mm RM spun on it.
Shilen is my vote.
There seams to be an issue with uploading photos from my I-phone. Is it just the Apple phone or are others having the same issue with a different platform.
For years I use the (#3031) Hornady 150gr SP out of my 308 Win for deer and very successful. Today’s marketing is all about high BC bullets. We’ve taken deer with bullets from 130gr to 210gr out of a 308 Win and all were just as dead.
I’ve went out on limb several times when new manufactures bring scopes to market. When Athlon came to market I ordered a Argos BTR 8-34 still have it and does what I expect from it. Bought several Athlons since.
Next one I tried was a Crimson Trace 2-series in 4-16 excellent scope except there...
The one thing I’m guessing it’s your annealing. I’ve found that some of my Peterson brass didn’t like annealing after one firing.
I would take a piece of the 2x brass that wasn’t annealed and keep sizing and firing it to see if working harding solves the carbon issue.