I use .265" bushings on the 4 dashers I load for. 2 shoot hydro formed brass, 2 fire formed. It's rare I measure a loaded rd, I go off consistent seating force and downrange results. 265 works in all 4. I just measured my 2 that shoot 110's, one .268", one .2685", I really have to be careful with these 2 as I can get gas coming back on the shoulders, so I do a partial size, more or less leaving a goiter on the necks. Neck dia in the chamber is .272" supposedly by reamer print.
If I was to buy my own reamer, I would opt for a .271" neck based on what I have experienced.
I just got a new phone, but had pics of groups at 1K using a .266" and a .265" bushing, the 1 thou added tension really brought it in. The load was a hammer at 500, opened up at 1K.
Even though I like the neck lengths of fireformed brass over hydro formed, the 2 shooting hydro formed seem to be more accurate rifles, not sure what that is indicative of.