I use a 5C collet. I haven't put too much effort into determining if they are dead true but I can tell you they certainly are not out by much if any. All the ones I've done seem to have almost no misalignment at all, a 1-2 thou cut off the lugs trues them up every time. The face is dished from the tumbling process and gets trued to the lugs with the same set up, its the only reason I machine the head in the first place. I remove the rad, tune the ejector depth, debur and install a new extractor detent ball.