I gotta agree with all that's been said about working dimensional tolerances and accuracy by you guys. And I totally agree with the concept that using a single cavity mold increases your chances of getting bullets with the minimum weight and size deviation. This seems to me to be a practical concept for rifle shooter seeking the best possible accuracy in a rifle. But its a tradeoff of production rate vs quality.
I have focused my efforts on producing multi-cavity molds made to achievable dimensional standards that will produce bullets of adequate accuracy for the intended use, intended primarily for handgun level cartridges. (The truth is, I'm trying to make a mold that I would want to buy, own, and use. I'm trying to satisfy ME.)
I think that if I can control the diameter and depth to -0.000 +.001 from hole to hole that will at least be as good as the mass (not custom) produced molds currently available. And by lathe boring I can compensate for tool wear by just moving the cross-slide out a little more, so as long as the tool wears evenly there shouldn't be any change in profile or overall decrease in hole sizes from start to end of a batch. And my experience has been that (a) a lathe bores a lot rounder hole than any milling machine, and (b) by keeping the blocks together during boring you eliminate a lot of the cutter wobble and cavity edge burring that comes from all sorts of places when using the traditional compound-vise-and-cherry method.
I'm sure other people have different needs and standards, but I think that a lot of people would be satisfied to have a five or six cavity handgun bullet mold that would drop all the bullets to the proper minimum size +0.001". But I could be wrong.
(Not a big sports fan, my only fascination with football is that unlike serialized television the outcome isn't really predictable from the start. I seen the same plots rehashed so many times that I can't even get interested in TV anymore unless its the History, Military or similar channel.)