Originally Posted by AZShooter
I discovered something interesting when I turned down the 30 BR brass to .0105" neck wall thickness.
While I had a bushing die I decided to see what the RCBS FL die would do without the expander ball. It was a perfect .002" reduction in neck diameter. I actually quit using the bushing die! I set up the die for the exact shoulder bump and used a feeler gauge to measure the space between shell holder and die. After that I could instantly setup the FL die.
Who knows your standard FL die might work perfectly without the sizer ball if you necks are the right dimension.
It is impossible for a standard FL die to "fit perfectly" for those 10 cases AND the others that are. .002 larger!
However that method you describe is a way to check out whether or not it will work for that gun and it normally solves runout issues.