Case mouth belling after FL sizing

[Webster]

Almost always 1.5 degrees.
I don’t understand your second question.
The third question is debatable. We all strive to make perfectly concentric ammo and I have shot my most concentric and least concentric ammo (4 thou delta in TIR) against each other and noticed no difference at 600 yards. I’ve performed this test several times over the past 5 years. It’s a good way for me to use up ammo that has been made with larger TIR.
Dave

I think you were commenting on my comments on the forcing cone. I assume the purpose of the forcing cone is to make the bullet enter the rifling as centered as possible with the bore center line.

My whole point was your striving to make the bullet in the neck with very little runout. Doesn't the forcing cone and smashing the rifling engraving into the bullet swamp anything you do with neck preparation?