Re: Concentricity..Issues or me?
Sounds like the seating die plunger is not bearing evenly on the ogive of your bullets. This forces the bullets crooked when seated. NO good.
Deepen the cavity in the plunger. Doesn't matter what you use. Just make sure that the tip is not bottoming out first. I would just take a Dremel to it. A drill might not be hard enough.
With this done, the bullet will now only contact the base of the plunger at the ogive. Way more consistent and usually solves seating runout issues. Of course, you can switch to another die if this persists as something else is hanging up.