Thank you all for your help. I finally got to look at it this weekend. It turns out that I was stupid (I hate admitting that). I wasn't varying anywhere near what I said I was.
From the last twenty rounds that I loaded (close to minimum OAL) I was between 1.100 and 1.108. That is higher than what char923 mentioned, but much lower than I was remembering (maybe I should cut back my electroshock therapy
).
I'd still like to get the depths closer together than this, but from Good Guy's post, it seems that I won't be with the 500B.