OzFclass

Yes
I do turn necks, but I don't use a tight neck chamber, I turn, or skim might be more correct for two reasons.
1. concentricity
2. neck tension
neck thickness is 0.0125". I use a 0.307 bush for sizing and a .2825 expander (this is for 7mm)

I am travelling until September and I am operating from a tablet so I can't really access all my data.

But I can say:
1. a .2825 mandrel produces tighter groups than a .2835 mandrel using the procedure described and
2. a tighter velocity spread, SD of around 6. this is across 20 rounds, not 5.

I don't think my rounds could be moved by hand.

Thanks.
I ended up with an average chrony SD of 6.8 for the .306 mandrel and 7.2 for the .3075, sample size is over a hundred for each.
I found the average MR is similar between the two however there were days that the .3075 absolutely hammered relative to the .306 mandrel loads.
I still need to pick apart the group size/MR/SD of those groups so there might be something I am missing there, but chrony data hasn't really shown anything up...but I am going to repeat on another barrel as maybe this barrel is the larger noise factor.

Yes, and the problem is attributing an improvement or it's opposite to one factor, when it might be something else entirely.
The rabbit hole