Just got a Sinclair concentricity gage and need some help evaluating what I am seeing, and what I might be able to do to fix it. I made up 20 rounds of 7-08 rem tonight, checking run-out on the necks during each step. Was working with twice fired Norma brass. Checked out the necks before I did anything, all were less than .002".
My first step was full length sizing. Redding series A dies. I size with the expander removed, and bump the shoulder .001"-.002". Necks after this sizing remained .002" or under.
I expand the necks using a neck sizing die (again Redding) with the die loose in the press, and the expander loose in the die. I feel this lets the expander find its own way as I push it down into the neck. To be clear here, I only run the case up high enough to push the expander through the neck, and then back it out. Most necks still ran .002" or under, with one or two of them at .003".
Primed and charged the cases.
On to the seating. Standard Redding series A seating die. I was loading Hornady 139 SPs. Was disappointed with what I found after seating. Indicator tip was running on the bearing surface of the bullet, just behind the ogive. Inconsistent is the best way to describe the readings. I would say almost half ran at .002" or under. Five or six of them ran between .003" and .004". The other four or five ran between .005" and .008".
This is the first time I've been able to check concentricity so would appreciate any insight you all might have. Something wrong with my process? Or perhaps this is somewhat typical with a standard seating die?
Thanks for the help.
