I use the Lee seater, which has worked pretty well with other rounds.
I checked case concentricity with the Sinclair, indicator on the neck following FL sizing and they weren't that true. I think the die oversizes the case neck and the expander pulls pretty hard coming out.
I believe the Collet neck sizer will correct this situation and don't think the seater is the problem.
But, it won't take long to find out...
DF
