Been using .400. Will try either the .375 or .350 a try to see if it makes any difference.
Ordered a Forster FL Dasher die and had to send it back because it was bottoming out on the press (COAX) without setting back the shoulder. Was using a Redding Type S FL die with a .265 bushing without the expander which gave me 30 psi of seating pressure. Had Forster ream the neck to .265 while they had it to trim. Set it up this evening and checked runout on three cases. All three cases had runout at the neck of .0005 or less using a Accuracy One Concentricity Tool and Starrett dial test indicator. Think I am going to like the die.