Well- after all this talk of .33" 00 buck, which is what I remembered buying, I went down and just checked my 5 pound box of Hornady - it's "0" buck, not "00" and it measures .321" to .323" when measured all whichiway around the balls. They look nice and round, but aren't quite. As I noted, they seem to shoot as well as the .311" cast from a Lee mould.
This out of roundness is most likely due to the manufacturing method which leaves a belt all the way around. IIRC from one of Dan's posts, the shot is then rolled to re-integrate the belt into the balls. All swaged spherical balls are made this way.
Next time out, I'll see how the .320" pure lead balls shoot, cast from the .319" Lee mould.
I'm sure each batch of balls come out at a slightly different size and quality. Much depends on the settings of the machinery and it's wear tolerances, just as in the machinery used in making jacketed bullets.