Ken - Please check to assure that you process of squaring the tubes with the end of the blank is highly precise. One of the largest cause of Out-of-Round I have observed occurs when the axis of the blank is not co-linear with mandrel.
Missed alignment with the process for setting the ends to be at a true right angle with the axis of the tube keeps the co-linear much closer. If not square, the bushings tend to "kink" a bit and the tolerance built into the system, allows out of round.
This slapped me in the face when putting steel shanks into a run of beer tap handles. I let some of the rods get installed at a slight angle to the axis of the tap and had out of round where the tap met the ferrull. (only blotched 4)