I’ve run into a wall with my mixed 223 brass that I made into 300. A majority of the case necks are too thick and I’m thinking that my Wilson s/s bbl has a tight chamber too. Brass with necks .010 thick or less seem to work with .308 sized bullets. I’ve ordered a Hornady neck trimmer tool from midway, will be here next week probably. Plus the trimmer tool will make the necks a uniform thickness which wouldn’t hurt the accuracy. Ideally, how thick should the neck on 300 brass be? 9-10 thousands? This may have been the reason that my upper sat in the safe for so long after I got it and started building loads. Oldtimers disease kicking in. But I’ll get it running this time. I’ve got a Dillon 550 out in the shop that could be cranking out .300’s.