One question I have is that the True Angle literature says run out is a by product of brass too thin on one side of the neck. I can understand that but can't reconcile fired brass that comes out of a chamber virtually perfect, but has excessive run out after resizing? I always figured sizing and imperfect seating was the culprit?
The 60K psi of firing form fitted the outside of the brass, where you measure runout, to the inside of the chamber. If the chamber is good then so will be the outside of the brass. (This assumes brass that isn't really bad.)
OK, now suppose the cases come out of the chamber reading straight on the outside. Also suppose the conventional size die is perfect, but the brass is thicker/thinner on one side of the neck. On the upstroke of the press ram the outside of the brass is formed to the contour of the die chamber. The outside of the brass is concentric at this time. But the hole inside the neck isn't. On the down stroke the expander, which is assumed perfectly centered in the perfect die, expands the hole and in the process tries to pull it to the center line. Voila, crooked brass.
