I got a sinclair concentricity gauge recently, and have been having a good play with it. It's confirmed what I had suspected - that I am somehow getting a lot of runout in my seating process. My .243 cases, sized in a lee collet neck die, have about .0015" of runout, max. However a loaded round can have anything from about .002" to .010" of runout. I'm using a Hornady seating die, and have tried it in both a RCBS rockchucker and a Lee turret press. I put a good chamfer on the case mouth but it doesn't appear to help. I have the same problem with my .223 loads that I am seating with a redding competition seater. How can I reduce the runout introduced in the process of seating the bullet?